Synthesis and Actions of Juvenile Hormones In Insect Development (MS Word)

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JH has multiple functions and a primary role of JH in insect development is to modulate ecdysone action. It is principally a morphogenetic hormone. Its action consists in reconstitution of the capability for growth of parts of the body which have lost it in the course of morphogenesis. All other changes observed in the body after the administration of JH are indirect consequences of this action and are due to the altered biochemical balance produced in the body by the changed proportion of metabolically active tissue. JH maintains the current commitment of the tissues and cells, whereas ecdysone causes both predifferentiative and differentiative cellular events that are necessary for the moult. Thus, when JH is present, a moult to a larval stage ensues. If JH is absent at the onset of the moult, metamorphosis occurs. Studies of the molecular mechanisms of JH action have been hampered by the failure to isolate its receptor(s). Recently, detailed studies of JH action have begun, and further studies should elucidate new aspects of the action of this unique molecule.

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Synthesis and Actions of Juvenile Hormones In Insect Development (MS Word)

  1. 1. M. Phil (Zoology), 2M. Phil (Zoology), 2ndndSemesterSemesterRoll: BUR MP ZOORoll: BUR MP ZOO No.: 2008 / 9No.: 2008 / 9Registration No.: 2546 of 2008 – 2009Registration No.: 2546 of 2008 – 2009The University of BurdwanThe University of BurdwanBurdwan – 713 104Burdwan – 713 104West Bengal, IndiaWest Bengal, IndiaTERM PAPER – ITERM PAPER – ISubmitted in Partial Fulfillment of the Requirement for theSubmitted in Partial Fulfillment of the Requirement for theDegree of Master of Philosophy (Science).Degree of Master of Philosophy (Science).April, 2009April, 2009
  2. 2. AcknowledgementAcknowledgementI express my deep sense of gratitude to Dr. Abhijit Mazumdar, Reader, Department ofI express my deep sense of gratitude to Dr. Abhijit Mazumdar, Reader, Department ofZoology, The University of Burdwan, for his invaluable, consistent and able guidanceZoology, The University of Burdwan, for his invaluable, consistent and able guidanceand all sorts of assistance in preparing this Review Work successful.and all sorts of assistance in preparing this Review Work successful.I pay my humble respect to Prof. Prasanta Kumar Chaudhuri, for rendering usefulI pay my humble respect to Prof. Prasanta Kumar Chaudhuri, for rendering usefulsuggestions and assistance, valuable suggestions and also for his counsel in order tosuggestions and assistance, valuable suggestions and also for his counsel in order tocompile as well as make it in fruition.compile as well as make it in fruition.I am equally grateful to Dr. Niladri Hazra, Reader and Head, Department ofI am equally grateful to Dr. Niladri Hazra, Reader and Head, Department ofZoology, The University of Burdwan for giving me constant encouragements andZoology, The University of Burdwan for giving me constant encouragements andnecessary informations as well as suggestions whenever it is necessary.necessary informations as well as suggestions whenever it is necessary.I am especially thankful to Prof. Tara Charan Banerjee, Prof. Anadi Prasad Nandi,I am especially thankful to Prof. Tara Charan Banerjee, Prof. Anadi Prasad Nandi,Dr. Padmanabha Chakrabarti, Dr. Goutam Chandra, Dr. Goutam Aditya, Dr. AnupamDr. Padmanabha Chakrabarti, Dr. Goutam Chandra, Dr. Goutam Aditya, Dr. AnupamBasu, Dr. Anandamay Barik, Dr. Soumendra Nath Chatterjee, Dr. Koushik Ghosh andBasu, Dr. Anandamay Barik, Dr. Soumendra Nath Chatterjee, Dr. Koushik Ghosh andDr. Sumedha Roy for sparing me some of their invaluable time and giving me someDr. Sumedha Roy for sparing me some of their invaluable time and giving me someimportant suggestions during preparing this Review Work.important suggestions during preparing this Review Work.Name of Mr. Amitava Nandi, Librarian of the Department of Zoology, TheName of Mr. Amitava Nandi, Librarian of the Department of Zoology, TheUniversity of Burdwan demands special mention for providing me required books andUniversity of Burdwan demands special mention for providing me required books andreview papers for preparing this Review Work Report.review papers for preparing this Review Work Report.Mr. Asif Hossain, Miss Mou Nandi, JRF Scholars and Mrs. Sangita Mitra, SRFMr. Asif Hossain, Miss Mou Nandi, JRF Scholars and Mrs. Sangita Mitra, SRFScholar of the Entomology Research Unit, The University of Burdwan for their timelyScholar of the Entomology Research Unit, The University of Burdwan for their timelyassistances in manifold ways in completing the works for which my appreciationassistances in manifold ways in completing the works for which my appreciationknown no bound.known no bound.Other Scholars of Zoology Department, The University of Burdwan to whom I amOther Scholars of Zoology Department, The University of Burdwan to whom I amindebted for various courtesies.indebted for various courtesies.Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 22
  3. 3. The liberal assistance of the non – teaching staffs and technical assistance of theThe liberal assistance of the non – teaching staffs and technical assistance of theTechnical Assistant of our Department is also acknowledged.Technical Assistant of our Department is also acknowledged.I would also like to thank Dr. Manas Mahapatra, Scientist and Director, SimultalaI would also like to thank Dr. Manas Mahapatra, Scientist and Director, SimultalaConservationist, an NGO working with Wildlife Institute of India, Dehradun, IndiaConservationist, an NGO working with Wildlife Institute of India, Dehradun, Indiafor giving me constant encouragements and necessary suggestions in preparing thisfor giving me constant encouragements and necessary suggestions in preparing thisReview Work Report extremely successful.Review Work Report extremely successful.I also take this opportunity to acknowledge the assistance, encouragements,I also take this opportunity to acknowledge the assistance, encouragements,appreciations and co – operations received from my entire classmates.appreciations and co – operations received from my entire classmates.I would also like to mention the name of my husband, Mr. Chandra Kanta De, butI would also like to mention the name of my husband, Mr. Chandra Kanta De, butfor whose unrelenting indulgences and patience with me, this Review Work Reportfor whose unrelenting indulgences and patience with me, this Review Work Reportwould never have made its journey to this printed form.would never have made its journey to this printed form.Lastly, but not the least, I would like to express my gratitude to my parents, parentLastly, but not the least, I would like to express my gratitude to my parents, parent– in laws and my sister for their constant encouragements and blessings on me.– in laws and my sister for their constant encouragements and blessings on me.----------------------------------------------------------------------------------------------------------------------------------------------SARAMITA DE (CHAKRAVASARAMITA DE (CHAKRAVARTI)RTI)M. Phil (Zoology),M. Phil (Zoology), 22ndndSemesterSemesterRoll:Roll: BUR MP ZOOBUR MP ZOO No.:No.: 2008 / 92008 / 9Registration No.:Registration No.: 2546 of 2008 – 20092546 of 2008 – 2009Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 33
  4. 4. C O N T E N T SC O N T E N T SPage No.(s)Page No.(s)●● Literature ReviewLiterature Review 66●● PrefacePreface 77●● Isolation of Juvenile HormonesIsolation of Juvenile Hormones 7 – 87 – 8●● Chemical Characteristics of Juvenile HormonesChemical Characteristics of Juvenile Hormones 8 – 128 – 12●● Juvenoids or JH Analogues (JHa)Juvenoids or JH Analogues (JHa) 12 – 1512 – 15›› History›› History 12 – 1312 – 13›› Chemical Nature›› Chemical Nature 13 – 1513 – 15●● The Mevalonate Pathway and Synthesis of theThe Mevalonate Pathway and Synthesis of theJuvenile Hormones in InsectsJuvenile Hormones in Insects16 – 2016 – 20›› The Formation of Juvenile Hormones›› The Formation of Juvenile Hormones 16 – 1716 – 17›› Juvenile Hormones’ Synthesis in the Corpora Allata›› Juvenile Hormones’ Synthesis in the Corpora Allata 17 – 1817 – 18›› Regulation›› Regulation 19 – 2019 – 20›› Cellular Receptors for JH›› Cellular Receptors for JH 2020●● Degradation of JHDegradation of JH 20 – 2120 – 21Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 44
  5. 5. ●● Mechanism of ActionsMechanism of Actions 22 – 2722 – 27›› Actions of Juvenile Hormones on Endocrine Systems›› Actions of Juvenile Hormones on Endocrine Systems 25 – 2625 – 26›› Roles of Juvenile Hormones in embryonic development›› Roles of Juvenile Hormones in embryonic development 26 – 2726 – 27›› Diapause›› Diapause 2727●● Molecular Actions of Juvenile HormonesMolecular Actions of Juvenile Hormones 28 – 3328 – 33›› Regulation of the Ecdysone – Induced Transcription›› Regulation of the Ecdysone – Induced TranscriptionFactor Cascade (ETFC)Factor Cascade (ETFC)29 – 3029 – 30›› Regulation of Cuticular Melanization›› Regulation of Cuticular Melanization 30 – 3130 – 31›› Larval Pupal Commitment›› Larval Pupal Commitment 31 – 3331 – 33●● Applications of JHs and JHa(s)Applications of JHs and JHa(s) 33 – 3533 – 35●● SummarySummary 3636●● ReferencesReferences 37 – 5037 – 50Literature ReviewLiterature ReviewSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 55
  6. 6. The first group of insect hormones was discovered in association with metamorphosis.The first group of insect hormones was discovered in association with metamorphosis.The preventing activity of corpus allatum in metamorphosis was first shown byThe preventing activity of corpus allatum in metamorphosis was first shown byWigglesworth (1935) in his classic parabiosis experiments withWigglesworth (1935) in his classic parabiosis experiments with Rhodnius prolixus.Rhodnius prolixus.Later in 1936, he demonstrated how 6Later in 1936, he demonstrated how 6ththinstar giant nymphs got changed eventuallyinstar giant nymphs got changed eventuallyfollowed by another moult into the giant imago. The author showed not only thefollowed by another moult into the giant imago. The author showed not only thesource of these inhibitory effects, but also provided the first definite evidence of itssource of these inhibitory effects, but also provided the first definite evidence of itshormonal character. Wigglesworth (1940) started use of juvenile hormone in lieu ofhormonal character. Wigglesworth (1940) started use of juvenile hormone in lieu ofthe original term ‘inhibitory hormone’ after its active role in producing larvalthe original term ‘inhibitory hormone’ after its active role in producing larvalcharacters in adults. Later a number of other authors for various other insect speciescharacters in adults. Later a number of other authors for various other insect speciesconfirmed this discovery, likewise – Bounhiol et al. (1965) forconfirmed this discovery, likewise – Bounhiol et al. (1965) for Bombyx moriBombyx mori;;Pflugfelder (1937) forPflugfelder (1937) for Carausius morosusCarausius morosus; Piepho (1938) for; Piepho (1938) for Galleria mellonellaGalleria mellonella. At. Atthe same time, Wigglesworth (1936) also discovered the effect of the corpora allatathe same time, Wigglesworth (1936) also discovered the effect of the corpora allatahormone on ovarian development. They confirmed those for a number of otherhormone on ovarian development. They confirmed those for a number of otherspecies whilst in others, such asspecies whilst in others, such as Bombyx moriBombyx mori, no ovarian control by a corresponding, no ovarian control by a correspondinghumoral factor was found. Such apparent contradiction between the inhibitory,humoral factor was found. Such apparent contradiction between the inhibitory,metamorphosis – suppressing effect of the corpora allata hormone and its totalmetamorphosis – suppressing effect of the corpora allata hormone and its totalmetabolism – increasing influence, suggested to a number of authors that there weremetabolism – increasing influence, suggested to a number of authors that there weretwo or more corpora allata hormones having different effects. All the available datatwo or more corpora allata hormones having different effects. All the available datawere then explained by the operation of a single substance, JH (Juvenile Hormone),were then explained by the operation of a single substance, JH (Juvenile Hormone),possessing the character of a growth hormone (Novák, 1951 and 1956). Thepossessing the character of a growth hormone (Novák, 1951 and 1956). Theinterordinal non – specificity of Juvenile Hormone (JH) was shown by theinterordinal non – specificity of Juvenile Hormone (JH) was shown by thetransplantation of corpora allata between Blattoptera and Hemiptera (Novák, 1949transplantation of corpora allata between Blattoptera and Hemiptera (Novák, 1949and 1951) and Phasmida and Lepidoptera (Piepho, 1950). Williams (1956),and 1951) and Phasmida and Lepidoptera (Piepho, 1950). Williams (1956),Schneiderman and Gilbert (1958) made the first attempts at elucidating the chemicalSchneiderman and Gilbert (1958) made the first attempts at elucidating the chemicalnature of Juvenile Hormone, using ether extracts of male abdomens of the Saturniidnature of Juvenile Hormone, using ether extracts of male abdomens of the SaturniidP. cecropiaP. cecropia. Röller and his co – workers (1965) determined its chemical structure for. Röller and his co – workers (1965) determined its chemical structure forthe first time.the first time.PrefacePrefaceSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 66
  7. 7. Insect development is under the control of two hormones, Ecdysone and JuvenileInsect development is under the control of two hormones, Ecdysone and JuvenileHormone. JH is a sesquiterpenoid molecule that modulates Ecdysone action andHormone. JH is a sesquiterpenoid molecule that modulates Ecdysone action andfunctions in prevention of adult differentiation, retention of larval structures andfunctions in prevention of adult differentiation, retention of larval structures andregulation of the ovarian maturation. JH is a regulator of insect development which isregulation of the ovarian maturation. JH is a regulator of insect development which issynthesized and released by the glandular corpora allata. α – Ecdysone (E) and itssynthesized and released by the glandular corpora allata. α – Ecdysone (E) and itsprecursors are synthesized by the prothoracic glands following stimulation byprecursors are synthesized by the prothoracic glands following stimulation byProthoracicotropic Hormone (PTTH), which is produced by neurosecretory cells inProthoracicotropic Hormone (PTTH), which is produced by neurosecretory cells inthe brain and is realesed from their terminals either in the corpora cardiaca or in thethe brain and is realesed from their terminals either in the corpora cardiaca or in thecorpora allata in the Lepidoptera. In Lepidoptera, the role of JH in insect developmentcorpora allata in the Lepidoptera. In Lepidoptera, the role of JH in insect developmentis well studied. The activity of the corpora allata is regulated by humoral factors suchis well studied. The activity of the corpora allata is regulated by humoral factors suchas allatotropin and allatostatin as well as by nervous connections. In addition toas allatotropin and allatostatin as well as by nervous connections. In addition tohaving multiple functions in blocking adult differentiation, retaining larval structures,having multiple functions in blocking adult differentiation, retaining larval structures,and regulating ovarian maturation, JH is a key player for phase polymorphism inand regulating ovarian maturation, JH is a key player for phase polymorphism inarmyworms, aphids and locusts and for caste differentiation in termites and ants.armyworms, aphids and locusts and for caste differentiation in termites and ants.Moulting is caused by 20 – hydroxyecdysone (E). The action of JH on development isMoulting is caused by 20 – hydroxyecdysone (E). The action of JH on development isalways associated with Ecdysone action. JH does not prevent Ecdysone action inalways associated with Ecdysone action. JH does not prevent Ecdysone action ininducing the moult, but modulates its action. In the haemolymph, JH usually binds toinducing the moult, but modulates its action. In the haemolymph, JH usually binds tothe haemolymph JH – binding protein, so that it is protected from metabolism by thethe haemolymph JH – binding protein, so that it is protected from metabolism by thegeneral esterases.general esterases.Isolation of Juvenile HormonesIsolation of Juvenile HormonesJH is present in the haemolymph throughout the larval (nymphal) life, through theJH is present in the haemolymph throughout the larval (nymphal) life, through thepenultimate instar, and its presence causes a larval (nymphal) moult when the 20Epenultimate instar, and its presence causes a larval (nymphal) moult when the 20Etiter increases. In the insect subclass Hemimetabola, JH is about during adulttiter increases. In the insect subclass Hemimetabola, JH is about during adultdevelopment in the last instar nymph. Its role in the regulation of pupation indevelopment in the last instar nymph. Its role in the regulation of pupation inHolometabola is much more complicated. Williams (1956) found that a lipid extractHolometabola is much more complicated. Williams (1956) found that a lipid extractfrom the abdomen offrom the abdomen of CecropiaCecropia males produced JH effects in Coleoptera (males produced JH effects in Coleoptera (TenebrioTenebriomolitormolitor, Schmialek and Wigglesworth, 1958 and 1961) and in Bugs and Cockroaches,, Schmialek and Wigglesworth, 1958 and 1961) and in Bugs and Cockroaches,etc. as well as inetc. as well as in H.H. ccecropiaecropia and other moths. Gilbert and Schneiderman (1957 andand other moths. Gilbert and Schneiderman (1957 andSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 77
  8. 8. 1960) and Schneiderman (1961) studied in details the occurrence of the active1960) and Schneiderman (1961) studied in details the occurrence of the activeprinciple in the body of theprinciple in the body of the Hyalophora cecropiaHyalophora cecropia silkworm during ontogeny. Röllersilkworm during ontogeny. Röllerand Bjerke (1965), Röller et al. (1965), and Röller et al. (1967) isolated the substancesand Bjerke (1965), Röller et al. (1965), and Röller et al. (1967) isolated the substancessimilar to the active component of the abdominal extract from adultsimilar to the active component of the abdominal extract from adult HyalophoraHyalophoracecropiacecropia males; afterwards Dahm et al. (1967), Röller et al. (1967) and several othersmales; afterwards Dahm et al. (1967), Röller et al. (1967) and several otherslike Meyer and Ax (1965), Meyer et al. (1968 and 1970), Meyer (1971) identified inlike Meyer and Ax (1965), Meyer et al. (1968 and 1970), Meyer (1971) identified insame laboratory and subsequently Loew et al. (1970) together with a key intermediatesame laboratory and subsequently Loew et al. (1970) together with a key intermediateto its synthesis (Mori, 1972) successfully synthesized in their laboratories.to its synthesis (Mori, 1972) successfully synthesized in their laboratories.Chemical Characteristics of Juvenile HormonesChemical Characteristics of Juvenile HormonesJH is a sesquiterpenoid compound produced in the cells of the corpora allata (CA),JH is a sesquiterpenoid compound produced in the cells of the corpora allata (CA),which are bilaterally paired structures in Lepidoptera, but are often fused into onewhich are bilaterally paired structures in Lepidoptera, but are often fused into onemass of tissue in other groups of insects. In 1956, the experiment by Williams on themass of tissue in other groups of insects. In 1956, the experiment by Williams on theH. cH. cecropiaecropia males facilitated the chemical identification of the active principle.males facilitated the chemical identification of the active principle. Of theOf themany workers who investigated the nature of thismany workers who investigated the nature of this ‘H. c‘H. cecropiaecropia oiloil’’, the most, the mostsuccessful were who succeeded in isolating the active principle by means of gassuccessful were who succeeded in isolating the active principle by means of gaschromatography. They proposed the chemical formula of malechromatography. They proposed the chemical formula of male H. cH. cecropiaecropia extract asextract asMethyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethyl – 2, 6 – tridecadienoate or MethylMethyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethyl – 2, 6 – tridecadienoate or Methyl– 12, 14 – dihomo juvenate (Meyer, 1970)– 12, 14 – dihomo juvenate (Meyer, 1970) Fig. (1)Fig. (1)..CHCH33CHCH33 CHCH22 CH3CH3 OOHH33CC CC CHCH22 CC CHCH22 CC C OCH3C OCH3CHCH22 O CHO CH CHCH22 CHCH CHCH22 CHCHFig. (1): - Chemical formula of MaleFig. (1): - Chemical formula of Male H. cH. cecropiaecropia extractextractAs seen from the followingAs seen from the following Table – (A)Table – (A),, thethe H. cH. cecropiaecropia JH content is fairly highJH content is fairly highin unfertilized eggs, during the embryonic period and in the freshly hatched larvae. Itin unfertilized eggs, during the embryonic period and in the freshly hatched larvae. ItSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 88
  9. 9. decreases at the end of larval development and in the pupa, practically disappearsdecreases at the end of larval development and in the pupa, practically disappearswhen development recommences after the pupal diapause and does not reappear untilwhen development recommences after the pupal diapause and does not reappear untiljust before adult emergence, when it increases slowly in the female, but rapidly in thejust before adult emergence, when it increases slowly in the female, but rapidly in themale.male.Table – (A): - Juvenile Hormone content ofTable – (A): - Juvenile Hormone content of H. cH. cecropiaecropia during developmentduring development(After Schneiderman, 1961)(After Schneiderman, 1961)Stages of DevelopmentStages of Development JH content / gm freshJH content / gm freshweight compared with adultweight compared with adultmale (in %)male (in %)1. Unfertilized Eggs1. Unfertilized Eggs 4.304.302. 7 – days old Embryos with yolk2. 7 – days old Embryos with yolk 3.703.703. 13. 1ststinstar larvae (freshly hatched)instar larvae (freshly hatched) 6.406.404. 54. 5ththinstar larvae (mixed ages)instar larvae (mixed ages) 0.500.505. Freshly moulted pupae5. Freshly moulted pupae 0.750.756. Diapausing Pupae (1 month old)6. Diapausing Pupae (1 month old) 0.550.557. Chilled Pupae (6 months old)7. Chilled Pupae (6 months old) 0.000.008. Pupae 2 days of adult development8. Pupae 2 days of adult development 0.000.009. Pupae 11 days of adult development9. Pupae 11 days of adult development 0.000.0010. Pupae 17 days of adult development10. Pupae 17 days of adult development 0.000.0011. Pupae 20 days of adult development11. Pupae 20 days of adult development 0.500.5012. Pupae 22 days of adult development (males)12. Pupae 22 days of adult development (males) 50.0050.0013. Adult males, 2 days old13. Adult males, 2 days old 100.00100.0014. Adult females, 2 days old14. Adult females, 2 days old 3.203.20Five JH variants (six, if one includes methylfarneosate, which is the immediateFive JH variants (six, if one includes methylfarneosate, which is the immediateprecursor of the JH molecules and which is secreted by some insects and has JHprecursor of the JH molecules and which is secreted by some insects and has JHactivity on its own) are known. The structures of JH I, JH II, JH III, JH 0 and the isoactivity on its own) are known. The structures of JH I, JH II, JH III, JH 0 and the isoJH 0 (also called 4 – methyl JH I) are shown inJH 0 (also called 4 – methyl JH I) are shown in Fig. (2)Fig. (2). Although JH III has most. Although JH III has mostoften been found as the principal or only JH molecule in many insects, more detailedoften been found as the principal or only JH molecule in many insects, more detailedanalyses with GC – Ms (Bergot et al., 1981) have shown multiple JHs in some insects,analyses with GC – Ms (Bergot et al., 1981) have shown multiple JHs in some insects,particularly Lepidoptera. JH III is only detectable as a trace, but JH I and JH II areparticularly Lepidoptera. JH III is only detectable as a trace, but JH I and JH II areoften the principal JHs. In addition, JH II acid and JH I acid are also released from theoften the principal JHs. In addition, JH II acid and JH I acid are also released from theCA. Although JH is the principal JH of early instars ofCA. Although JH is the principal JH of early instars of Manduca sextaManduca sexta (Schooley et(Schooley etSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 99
  10. 10. al., 1984), production of the JH acids seems to be the normal process in the last instaral., 1984), production of the JH acids seems to be the normal process in the last instarofof M. sextaM. sexta, which loses the enzymatic ability to methylate the final step in synthesis, which loses the enzymatic ability to methylate the final step in synthesisof the various JHs (Bhaskaran et al., 1986).of the various JHs (Bhaskaran et al., 1986).(Cntd. to next page)(Cntd. to next page)Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect DevelopmentCOOCH3OCH3iso JH 04 – methyl JH ICOOCH3OCH3JH 0COOCH3OCH3JH ICOOCH3OCH3JH II1010
  11. 11. Methyl – 10, 11 – epoxy -, 7, 11 – trimethyl – 2 – trans –Methyl – 10, 11 – epoxy -, 7, 11 – trimethyl – 2 – trans –6 – trans - dodecadienoate6 – trans - dodecadienoateJH bisepoxideJH bisepoxideFig. (2): - Molecules with juvenile hormone (JH) activityFig. (2): - Molecules with juvenile hormone (JH) activity[JH III may be the most common JH of insects; JH I, JH II, JH III, JH 0 and iso JH 0 have[JH III may be the most common JH of insects; JH I, JH II, JH III, JH 0 and iso JH 0 havebeen found in some Lepidoptera. JH bisepoxide is synthesized by the ring gland of Diptera.]been found in some Lepidoptera. JH bisepoxide is synthesized by the ring gland of Diptera.]JH acid production continues into the pupal and adult stages. The JH acids haveJH acid production continues into the pupal and adult stages. The JH acids havelittle biological activity, but they can be methylated slowly in imaginal disc tissueslittle biological activity, but they can be methylated slowly in imaginal disc tissues(Sparagana et al., 1985) and the slow methylation may be important to overall(Sparagana et al., 1985) and the slow methylation may be important to overallfunction of JH and metamorphosis infunction of JH and metamorphosis in M. sextaM. sexta and possibly other Lepidoptera (Gilbertand possibly other Lepidoptera (Gilbertet al., 1996). JH bisepoxide (JHB3) is the principal JH ofet al., 1996). JH bisepoxide (JHB3) is the principal JH of Drosophila melanogasterDrosophila melanogaster(Richard et al., 1989) and in some other insects. JH molecules have chiral centers, and(Richard et al., 1989) and in some other insects. JH molecules have chiral centers, andtheir natural enantiomers may be more active and less rapidly degraded than unnaturaltheir natural enantiomers may be more active and less rapidly degraded than unnaturalenantiomers. (Tobe and King, 1993). JH II has a chiral center at Cenantiomers. (Tobe and King, 1993). JH II has a chiral center at C1010 and the other JHand the other JHmolecules have chiral centers at Cmolecules have chiral centers at C1010 and Cand C1111. JHB3 has three chiral centers at C. JHB3 has three chiral centers at C66, C, C77and Cand C1010..Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect DevelopmentCOOCH3OCH3JH IIICOOCH3CH3 OO1111
  12. 12. Juvenoids or JH Analogues (JHa)Juvenoids or JH Analogues (JHa)Since the metamorphosis hormones and their effects were discovered, a number ofSince the metamorphosis hormones and their effects were discovered, a number ofsubstances possessing physiological activity more or less identical with that of somesubstances possessing physiological activity more or less identical with that of someof the insect hormones have been found in extracts of other animal tissues and variousof the insect hormones have been found in extracts of other animal tissues and variousplants. The first of these was the isoprenoid alcohol, farnesol, whose juvenilizingplants. The first of these was the isoprenoid alcohol, farnesol, whose juvenilizingeffects were found in the brain extracts (Schmialek and Wigglesworth, 1959 andeffects were found in the brain extracts (Schmialek and Wigglesworth, 1959 and1961). As soon as practical implications of substances with this type of effect became1961). As soon as practical implications of substances with this type of effect becameevident, chemists immediately turned their attention to this problem, with the resultevident, chemists immediately turned their attention to this problem, with the resultthat, to date, over 1000 synthetic Juvenoids or JHa have been produced. The greatthat, to date, over 1000 synthetic Juvenoids or JHa have been produced. The greattheoretical importance of JHa is that they can be used to analyze all problems oftheoretical importance of JHa is that they can be used to analyze all problems ofinsect growth and morphogenesis far more easily and thoroughly than by the corporainsect growth and morphogenesis far more easily and thoroughly than by the corporaallata transplantation method, which was employed before their discovery. From theallata transplantation method, which was employed before their discovery. From thepractical aspect, their main promise and immense importance is that they offerpractical aspect, their main promise and immense importance is that they offerprospects of biological control of new types.prospects of biological control of new types.HistoryHistoryThe history of the discovery of substances of this type dates back only a few yearsThe history of the discovery of substances of this type dates back only a few yearsand its rapid development keeps pace with the development of insect endocrinologyand its rapid development keeps pace with the development of insect endocrinologyor ahead of it. The prelude to this was the discovery that the abdomens of the matureor ahead of it. The prelude to this was the discovery that the abdomens of the matureHyalophora cecropiaHyalophora cecropia male contained a large amount of a substance whose effectsmale contained a large amount of a substance whose effectscorrespond with those of JH and which could be isolated by simple extraction withcorrespond with those of JH and which could be isolated by simple extraction withethyl ether or methanol (Williams, 1956). Extracts from related species, or even fromethyl ether or methanol (Williams, 1956). Extracts from related species, or even fromthe female of the same species displayed little or no JH activity at all. Soon afterthe female of the same species displayed little or no JH activity at all. Soon afterWilliams’ workout and finding, discovery of ether extracts of the most diverse tissuesWilliams’ workout and finding, discovery of ether extracts of the most diverse tissuesshowed similar JH effects. In addition to the tissues of insects and other invertebrates,showed similar JH effects. In addition to the tissues of insects and other invertebrates,these included cow’s milk and later on, tissue extracts from many plants and micro –these included cow’s milk and later on, tissue extracts from many plants and micro –organisms (Schneiderman, 1960 and Gilbert, 1964). Schmialek (1961) working inorganisms (Schneiderman, 1960 and Gilbert, 1964). Schmialek (1961) working incollaboration with Karlson (1965) and with Wigglesworth (1961), showed that acollaboration with Karlson (1965) and with Wigglesworth (1961), showed that aSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1212
  13. 13. relatively simple alcohol of plant origin, i.e., farnesol and a number of its derivatives,relatively simple alcohol of plant origin, i.e., farnesol and a number of its derivatives,were also highly effective when administered in the same manner. Shortly afterwards,were also highly effective when administered in the same manner. Shortly afterwards,Sláma (1963) disclosed that various saturated and unsaturated fatty acids, certain fattySláma (1963) disclosed that various saturated and unsaturated fatty acids, certain fattyalcohols and other natural and synthetic compounds produced juvenilizing effects ofalcohols and other natural and synthetic compounds produced juvenilizing effects ofvarying intensity.varying intensity.Chemical NatureChemical NatureThe substances so far known, whether synthesized or isolated from various materialsThe substances so far known, whether synthesized or isolated from various materialsof vegetables and other origin, can be divided into the following eight groupsof vegetables and other origin, can be divided into the following eight groupsaccording to their chemical structure (Sláma, 1971). Substances similar to the activeaccording to their chemical structure (Sláma, 1971). Substances similar to the activecomponent of the abdominal extract of malecomponent of the abdominal extract of male H. cH. cecropiaecropia (adult), isolated by Röller et(adult), isolated by Röller etal. (1965) and others shown to be Methyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethylal. (1965) and others shown to be Methyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethyl– 2, 6 – tridecadienoate (JH I)or Methyl – 12, 14 – dihomo juvenate (JH II) (Meyer,– 2, 6 – tridecadienoate (JH I)or Methyl – 12, 14 – dihomo juvenate (JH II) (Meyer,1970). One 6 – 7 days old male1970). One 6 – 7 days old male Hyalophora cecropiaHyalophora cecropia abdomen contained 0.2 – 0.5 µgabdomen contained 0.2 – 0.5 µgJH I and 0.02 – 0.12 µg JH II. The stereochemistry of JH I and the biological activityJH I and 0.02 – 0.12 µg JH II. The stereochemistry of JH I and the biological activity(ranging from 1 to 5000 Tu / µg) of some of its isomers and related compounds have(ranging from 1 to 5000 Tu / µg) of some of its isomers and related compounds havebeen determined (Dahm et al., 1968)been determined (Dahm et al., 1968) Table – (B)Table – (B). The nearest to the preceding group. The nearest to the preceding groupare acrylic terpenoids, which are similar to farnesenic acid derivatives, but lack theare acrylic terpenoids, which are similar to farnesenic acid derivatives, but lack theepoxy group and have a methyl instead of ethyl radical at Cepoxy group and have a methyl instead of ethyl radical at C1717 and Cand C1111. This group. This groupcomprises the most well studied JHa, such as Dichloro – dimethyl – farnesoate.comprises the most well studied JHa, such as Dichloro – dimethyl – farnesoate.Aromatic ethers, thio – ethers and amines form he largest JHa group. They are mostlyAromatic ethers, thio – ethers and amines form he largest JHa group. They are mostlyphenol or aniline derivatives in the ortho position, with a differently modified orphenol or aniline derivatives in the ortho position, with a differently modified orsubstituted acrylic, mono or sesquiterpenic chain. Monocyclic sesquiterpenoids, tosubstituted acrylic, mono or sesquiterpenic chain. Monocyclic sesquiterpenoids, towhich the paper factor, or Juvabione, and its derivatives belong. They are active onlywhich the paper factor, or Juvabione, and its derivatives belong. They are active onlyin bugs of Pyrrhocoridae family. Certain fatty acids and alcohols (both saturated andin bugs of Pyrrhocoridae family. Certain fatty acids and alcohols (both saturated andunsaturated fatty acids) and some of their derivatives, demonstrated for the first timeunsaturated fatty acids) and some of their derivatives, demonstrated for the first timeby Sláma (1962 and 1963). The most recently discovered group of compounds with aby Sláma (1962 and 1963). The most recently discovered group of compounds with apeptide structure (Zaoral and Sláma, 1970) whose derivatives are all composed of 2 –peptide structure (Zaoral and Sláma, 1970) whose derivatives are all composed of 2 –3 amino acids and a branched aliphatic residues. The most active is the L – isoleucyl –3 amino acids and a branched aliphatic residues. The most active is the L – isoleucyl –Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1313
  14. 14. L – alanyl – aminobenzoic acid ethyl ester, which in Pyrrhocoris is twice as active asL – alanyl – aminobenzoic acid ethyl ester, which in Pyrrhocoris is twice as active asJuvabione. Its Chemical Structure is asJuvabione. Its Chemical Structure is as Fig. (3)Fig. (3)..OONNHH COOCCOOC22HH55NNHHNHNH22 OOFig. (3): - Chemical Structure of the most activeFig. (3): - Chemical Structure of the most activeJH AnalogueJH AnalogueTable – (B): - Biological activity and RTable – (B): - Biological activity and RFF values of the authenticvalues of the authenticjuvenile hormone and the synthesized compounds*juvenile hormone and the synthesized compounds*(After Dahm et al., 1968)(After Dahm et al., 1968)Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1414
  15. 15. Name of the CompoundName of the Compound Specific ActivitySpecific Activity(Tu / µg)(Tu / µg) ****RRFF******1. t, t – C1. t, t – C1212 – ethyl – ester (VI)– ethyl – ester (VI) Inactive (at 10µg / animal)Inactive (at 10µg / animal) 0.670.672. c, t – C2. c, t – C1212 – ethyl – ester– ethyl – ester Inactive (at 10µg / animal)Inactive (at 10µg / animal) 0.710.713. t, t – C3. t, t – C1515 – ketone (VIII)– ketone (VIII) 55 0.480.484. t, t, t – C4. t, t, t – C1717 – methyl – ester (IX)– methyl – ester (IX) 200200 0.670.675. t, c, t – C5. t, c, t – C1717 – methyl – ester– methyl – ester 3030 0.670.676. c, t, t – C6. c, t, t – C1717 – methyl – ester– methyl – ester 11 0.730.737. c, c, t – C7. c, c, t – C1717 – methyl – ester– methyl – ester 11 0.730.738. dl – t, t, t – 10 – epoxy – C8. dl – t, t, t – 10 – epoxy – C1717 – methyl – ester (X)– methyl – ester (X) 20002000 0.400.409. dl – t, c, t – 10 – epoxy – C9. dl – t, c, t – 10 – epoxy – C1717 – methyl – ester (XIII)– methyl – ester (XIII) 150150 0.400.4010. dl – t, c, t – 10 – epoxy – C10. dl – t, c, t – 10 – epoxy – C1717 – methyl – ester (XIV)– methyl – ester (XIV) 1010 0.410.4111. dl – c, c, t – 10 – epoxy – C11. dl – c, c, t – 10 – epoxy – C1717 – methyl – ester (XV)– methyl – ester (XV) 1010 0.410.4112. dl – t, t, t – 6 – epoxy – C12. dl – t, t, t – 6 – epoxy – C1717 – methyl – ester (XI)– methyl – ester (XI) 200200 0.440.4413. Juvenile Hormone (from13. Juvenile Hormone (from H. cH. cecropiaecropia oil)oil) 200200 0.400.40** = All compounds were obtained by gas chromatography in pure state= All compounds were obtained by gas chromatography in pure state**** = Tu / µg means Tenebrio Units per Microgram= Tu / µg means Tenebrio Units per Microgram****** = Thin Layer Chromatography on Silica Gel G (E. Merck) activated 2 hrs. at= Thin Layer Chromatography on Silica Gel G (E. Merck) activated 2 hrs. at120ºC, Benzene:Ethyl acetate = 15:1120ºC, Benzene:Ethyl acetate = 15:1The Mevalonate Pathway and Synthesis of the JuvenileThe Mevalonate Pathway and Synthesis of the JuvenileHormones in InsectsHormones in InsectsThe mevalonate pathway in insects has two important peculiarities, the absence of theThe mevalonate pathway in insects has two important peculiarities, the absence of thesterol branch and the synthesis of juvenile hormone (JH) that may have influenced thesterol branch and the synthesis of juvenile hormone (JH) that may have influenced themechanisms of regulation. JH modulates transcript levels of a number of genes of themechanisms of regulation. JH modulates transcript levels of a number of genes of themevalonate pathway or can influence the translatability and / or stability of themevalonate pathway or can influence the translatability and / or stability of thetranscripts themselves. The mevalonate pathway is a ramified metabolic route basedtranscripts themselves. The mevalonate pathway is a ramified metabolic route basedon reductive polymerization of acetyl – CoA, which leads to a great diversity ofon reductive polymerization of acetyl – CoA, which leads to a great diversity ofisopenoid compounds. Final products of the pathway also include hormonalisopenoid compounds. Final products of the pathway also include hormonalSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1515
  16. 16. messengers, such as cytokinins and phytoalexins in plants, steroid hormones inmessengers, such as cytokinins and phytoalexins in plants, steroid hormones inmammals and defensive secretions, pheromones and JH in insects.mammals and defensive secretions, pheromones and JH in insects.The Formation of Juvenile HormonesThe Formation of Juvenile HormonesThe conversion of farnesol to farnesal was believed to be catalyzed by a nicotinamideThe conversion of farnesol to farnesal was believed to be catalyzed by a nicotinamide– dependent dehydrogenase, but recent studies in the lepidopteran– dependent dehydrogenase, but recent studies in the lepidopteran Manduca sextaManduca sextasuggest that it is a metal – or – flavin – dependent oxidase. In orthopteroid insects,suggest that it is a metal – or – flavin – dependent oxidase. In orthopteroid insects,esterification of farnesoic acid occurs before epoxidation precedes esterification,esterification of farnesoic acid occurs before epoxidation precedes esterification,which is under developmental control, and the corresponding JH methyl transferasewhich is under developmental control, and the corresponding JH methyl transferasewas cloned fromwas cloned from B. moriB. mori. JH methyl transferase transfers a methyl group of S –. JH methyl transferase transfers a methyl group of S –adenosyl – L – methionine (SAM) to farnesoic acid or epoxyfarnesoic acid. Thus, it isadenosyl – L – methionine (SAM) to farnesoic acid or epoxyfarnesoic acid. Thus, it isnot strange that the amino acid sequences of the insect JH methyl transferase containnot strange that the amino acid sequences of the insect JH methyl transferase containconserved SAM – binding motif typical of the family of SAM – dependent methylconserved SAM – binding motif typical of the family of SAM – dependent methyltransferases. Orthologs of insect JH methyl transferases from a number of crustaceantransferases. Orthologs of insect JH methyl transferases from a number of crustaceanspecies are known. More, recently, a specific JH epoxidase has been cloned andspecies are known. More, recently, a specific JH epoxidase has been cloned andcharacterized from the corpora allata (CA) of the cockroachcharacterized from the corpora allata (CA) of the cockroach Diploptera punctataDiploptera punctataTable – (C)Table – (C). It belongs to the large superfamily of cytochrome P450 proteins and. It belongs to the large superfamily of cytochrome P450 proteins andepoxidizes methyl farnesoate with high regio- and stereo- selectivity. A clear orthologepoxidizes methyl farnesoate with high regio- and stereo- selectivity. A clear orthologof this JH epoxidase has been identified in the genome ofof this JH epoxidase has been identified in the genome of Anopheles gambiaeAnopheles gambiae,,whereas structurally related sequences have been found inwhereas structurally related sequences have been found in B. moriB. mori andand D.D.melanogastermelanogaster..Table – (C): - Species in which genomic or cDNA sequences for enzymes ofTable – (C): - Species in which genomic or cDNA sequences for enzymes ofthe mevalonate pathway and juvenile hormone synthesis are available.the mevalonate pathway and juvenile hormone synthesis are available.EnzymesEnzymes SpeciesSpeciesBombyx moriBombyx moriAnopheles gambiaeAnopheles gambiaeSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1616
  17. 17. JH methyl transferase.JH methyl transferase.Manduca sextaManduca sextaDrosophila melanogasterDrosophila melanogasterCallosobruchus maculatesCallosobruchus maculatesApis melliferaApis melliferaJH epoxidaseJH epoxidaseDiploptera punctataDiploptera punctataAnopheles gambiaeAnopheles gambiaeJuvenile Hormones’ Synthesis in the Corpora AllataJuvenile Hormones’ Synthesis in the Corpora AllataBiochemical informations implicate the mevalonate pathway in the synthesis of JH,Biochemical informations implicate the mevalonate pathway in the synthesis of JH,including data from studies on the production of JH by the CA, which showed that theincluding data from studies on the production of JH by the CA, which showed that theaddition of precursors such as mevalonate, farnesol, or farnesoic acid increased JHaddition of precursors such as mevalonate, farnesol, or farnesoic acid increased JHproduction, whereas the use of HMG – R inhibitors such as compactin or meviloninproduction, whereas the use of HMG – R inhibitors such as compactin or mevilonindecrease it, thus indicating that isopenoid flux modulates the rates of JH synthesisdecrease it, thus indicating that isopenoid flux modulates the rates of JH synthesis(Bellés et al., 2004)(Bellés et al., 2004) Fig. (4)Fig. (4)..Acetyl – CoAAcetyl – CoAAcetoacetyl – CoA thiolaseAcetoacetyl – CoA thiolaseAcetoacetyl – CoAAcetoacetyl – CoA3 – Hydroxy – 3 – methylglutaryl – CoA synthase3 – Hydroxy – 3 – methylglutaryl – CoA synthase(HMG – S)(HMG – S)Hydroxymethylglutharyl – CoAHydroxymethylglutharyl – CoA3 – Hydroxy – 3 – methylglutaryl – CoA reductase3 – Hydroxy – 3 – methylglutaryl – CoA reductase(HMG – R)(HMG – R)MevalonateMevalonateMevalonate kinaseMevalonate kinaseMevalonate – 5 – PMevalonate – 5 – PPhosphomevalonate kinasePhosphomevalonate kinaseMevalonate – 5 – PPMevalonate – 5 – PPDiphosphomevalonate decarboxylaseDiphosphomevalonate decarboxylaseIsopentenyl AdenineIsopentenyl Adenine Isopentenyl – PPIsopentenyl – PP Dimethyl allyl – PPDimethyl allyl – PP(tRNA)(tRNA)Geranyl – PPGeranyl – PPSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1717
  18. 18. Farnesyl diphosphate synthase (FPPS)Farnesyl diphosphate synthase (FPPS)DolicholDolichol Farnesyl – PPFarnesyl – PP SqualeneSqualeneHeme AHeme A Farnesyl diphosphateFarnesyl diphosphate synthasesynthaseUbiquinoneUbiquinone pyrophosphatasepyrophosphatasePrenylated ProteinsPrenylated ProteinsFarnesolFarnesol SqualeneSqualeneSqualeneSqualeneFarnesol oxidaseFarnesol oxidase monomonooxigenaseoxigenaseFarnesalFarnesal Squalene epoxideSqualene epoxideLanosterolLanosterolFarnesal dehydrogenaseFarnesal dehydrogenase synthasesynthaseJUVENILEJUVENILEFarnesoic AcidFarnesoic Acid LanosterolLanosterolHORMONESHORMONESJH methyl transferaseJH methyl transferaseBRANCHBRANCHMethyl farnesoateMethyl farnesoate CHOLESTEROLCHOLESTEROLIN INSECTSIN INSECTS JH epoxidaseJH epoxidaseLost in InsectsLost in InsectsJUVENILE HORMONESJUVENILE HORMONESFig. (4): - Flux Diagram of the Mevalonate Pathway andFig. (4): - Flux Diagram of the Mevalonate Pathway andJH Biosynthesis in Insects (Nation, 2002)JH Biosynthesis in Insects (Nation, 2002)RegulationRegulationUnveiling the regulatory mechanisms of the Mevalonate Pathway and the synthesis ofUnveiling the regulatory mechanisms of the Mevalonate Pathway and the synthesis ofJH in insects is a major challenge in the field of Entomology. Different studies haveJH in insects is a major challenge in the field of Entomology. Different studies haveshown that JH itself is a key regulatory element of the pathway at least in selectedshown that JH itself is a key regulatory element of the pathway at least in selectedinsect models and processes. In insects, cholesterol does not regulate the Mevalonateinsect models and processes. In insects, cholesterol does not regulate the Mevalonatepathway, rather than SREBP pathway (Sterol – dependent regulation) plays thatpathway, rather than SREBP pathway (Sterol – dependent regulation) plays thatpivotal role. Insect SREBP pathway would be homologous to the SREBP – 1c systempivotal role. Insect SREBP pathway would be homologous to the SREBP – 1c systemof mammals (Goldstein and Brown, 1990). In Scolytids, biochemical analysisof mammals (Goldstein and Brown, 1990). In Scolytids, biochemical analysisdemonstrated that JH regulates isoprenoid pheromone production de novo in thedemonstrated that JH regulates isoprenoid pheromone production de novo in themidgut ofmidgut of I. piniI. pini males. Further, analysis revealed that JH increases mRNA levels ofmales. Further, analysis revealed that JH increases mRNA levels ofHMG – R and HMG – S inHMG – R and HMG – S in I. paraconfususI. paraconfusus,, I. piniI. pini andand D. jeffreyiD. jeffreyi although there werealthough there weredifferences among these species in terms of dose dependency and timing of induction.differences among these species in terms of dose dependency and timing of induction.Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1818
  19. 19. JH activated HMG – R more strongly (8 folds inJH activated HMG – R more strongly (8 folds in I. piniI. pini and 30 folds inand 30 folds in D. jeffreyiD. jeffreyi))than HMG – S (4 folds inthan HMG – S (4 folds in D. jeffreyiD. jeffreyi). Moreover, JH elicited a modest induction of). Moreover, JH elicited a modest induction ofgeranyl diphosphate synthase expression in malegeranyl diphosphate synthase expression in male I. piniI. pini. A recent study on. A recent study on I. piniI. piniusing quantitative real – time PCR examined feeding – induced changes in geneusing quantitative real – time PCR examined feeding – induced changes in geneexpression of seven mevalonate pathway genes, namely acetoacetyl – CoA thiolase,expression of seven mevalonate pathway genes, namely acetoacetyl – CoA thiolase,HMG – S, HMG – R, diphosphomevalonate decarboxylase, isopentenyl diphosphateHMG – S, HMG – R, diphosphomevalonate decarboxylase, isopentenyl diphosphateisomerase, geranyl diphosphate synthase and FPPs. After feeding, expression in allisomerase, geranyl diphosphate synthase and FPPs. After feeding, expression in allseven genes increased in males, but only first five genes increased in females. Thisseven genes increased in males, but only first five genes increased in females. Thissuggests that feeding stimulates JH biosynthesis in the corpora allata, which, inturnsuggests that feeding stimulates JH biosynthesis in the corpora allata, which, inturnstimulates the enzymes involved in the anterior midgut of males. Investigations on thestimulates the enzymes involved in the anterior midgut of males. Investigations on therole of JH in the regulation of the mevalonate pathway in cockroach (role of JH in the regulation of the mevalonate pathway in cockroach (B. germanicaB. germanica))suggests that JH may regulate the translatability and (or the stability of the enzymesuggests that JH may regulate the translatability and (or the stability of the enzymetranscripts).transcripts).Research focused on JH, working on two different models: - the production of theResearch focused on JH, working on two different models: - the production of thepheromones in male Scolytids and the synthesis of JH and other processes related topheromones in male Scolytids and the synthesis of JH and other processes related tocockroach female reproduction. Results suggested that JH can exert a pleiotropic rolecockroach female reproduction. Results suggested that JH can exert a pleiotropic roleupon regulation of the mevalonate pathway, acting in some tissues stages, andupon regulation of the mevalonate pathway, acting in some tissues stages, andassociated physiological processes as a transcriptional activator (pheromoneassociated physiological processes as a transcriptional activator (pheromonebiosynthesis in Scolytids; and also modulating the translatability and / or stability ofbiosynthesis in Scolytids; and also modulating the translatability and / or stability ofthe transcripts themselves / processes related to reproduction in cockroaches). Often,the transcripts themselves / processes related to reproduction in cockroaches). Often,data have shown that JH can act in parallel with a number of enzymes in the pathway,data have shown that JH can act in parallel with a number of enzymes in the pathway,which suggest that the mevalonate pathway in insects can best be interpreted in termswhich suggest that the mevalonate pathway in insects can best be interpreted in termsof co – ordinated regulation and metabolic control analysis, rather than in terms of aof co – ordinated regulation and metabolic control analysis, rather than in terms of akey regulatory step (s).key regulatory step (s).Cellular Receptors for JHCellular Receptors for JHA number of studies have shown that the various JH molecules are bound toA number of studies have shown that the various JH molecules are bound tohaemolymph components and to cytoplasmic and nuclear proteins (Goodman andhaemolymph components and to cytoplasmic and nuclear proteins (Goodman andChang, 1985). A 29 kDa nuclear protein has been isolated from larval epidermal andChang, 1985). A 29 kDa nuclear protein has been isolated from larval epidermal andSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 1919
  20. 20. fat body cells offat body cells of M. sextaM. sexta with high specificity for binding JH I and JH II (Riddiford,with high specificity for binding JH I and JH II (Riddiford,1990; Riddiford and Truman, 1993). This nuclear binding protein is not present in the1990; Riddiford and Truman, 1993). This nuclear binding protein is not present in thenuclei of epidermal cells when no high – affinity JH binding sites are present, such asnuclei of epidermal cells when no high – affinity JH binding sites are present, such asin wandering larvae or in those larvae that are allatectomized. This protein isin wandering larvae or in those larvae that are allatectomized. This protein isconsidered a putative JH receptor. Another JH receptor has been purified from fatconsidered a putative JH receptor. Another JH receptor has been purified from fatbody cells of both adult sexes of the cockroachbody cells of both adult sexes of the cockroach Leucophaea manderaeLeucophaea manderae (Engelman,(Engelman,1995). It is a binding protein of about 64 kDa composed of two 32 kDa subunits. This1995). It is a binding protein of about 64 kDa composed of two 32 kDa subunits. ThisJH receptor appears to be more related to the egg production in the adult than to theJH receptor appears to be more related to the egg production in the adult than to thedevelopment of immature stages. At present, the receptor has only been detected I thedevelopment of immature stages. At present, the receptor has only been detected I thelast instar and adult, both stages capable of responding to exogenous JH or JH analoglast instar and adult, both stages capable of responding to exogenous JH or JH analogby synthesizing vitellogenin (in females) for incorporation into eggs.by synthesizing vitellogenin (in females) for incorporation into eggs.Degradation of JHDegradation of JHThe main degradative pathways for JH involve specific and non – specific. JHThe main degradative pathways for JH involve specific and non – specific. JHesterases (JHEs) described from numerous insects and JH epoxide hydrolasesesterases (JHEs) described from numerous insects and JH epoxide hydrolases(JHEHs) reported from some insects. The esterases attack the ester linkage, while(JHEHs) reported from some insects. The esterases attack the ester linkage, whileepoxide hydrolases open the epoxide ring and create a diolepoxide hydrolases open the epoxide ring and create a diol Fig. (5)Fig. (5).. Only one, or bothOnly one, or bothactions, occur in some insects. The metabolic changes not only eliminate all or mostactions, occur in some insects. The metabolic changes not only eliminate all or mostof the hormonal activity of the molecules, but those become more water soluble andof the hormonal activity of the molecules, but those become more water soluble andcan be excreted by the Malpighian tubules.can be excreted by the Malpighian tubules.Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect DevelopmentOOCH3JH I2020O OO
  21. 21. A.A. JH I diol.JH I diol. B.B. JH I acid.JH I acid.(Inactive)(Inactive) (Inactive)(Inactive)C.C. acid – diol form.acid – diol form.(Inactive)(Inactive)Fig. (5): - Metabolic pathways for the degradation of JHFig. (5): - Metabolic pathways for the degradation of JH[The epoxide ring can be opened with hydrolysis and production of two hydroxyl groups , as[The epoxide ring can be opened with hydrolysis and production of two hydroxyl groups , asin (in (AA), or the ester group can be hydrolyzed to the free acid as in (), or the ester group can be hydrolyzed to the free acid as in (BB), Both (), Both (AA) and () and (BB) are) areinactive, and either or both can occur in most insects (White, 1972)]inactive, and either or both can occur in most insects (White, 1972)]Mechanism of ActionsMechanism of ActionsVarious theories can explain the mode of action of JH, some obviously contradictory.Various theories can explain the mode of action of JH, some obviously contradictory.According to Wigglesworth’s original idea (1936), JH affects morphogenesis on theAccording to Wigglesworth’s original idea (1936), JH affects morphogenesis on theprinciple of Goldschmidt’s hypothesis of different reaction velocities. Novák (1951principle of Goldschmidt’s hypothesis of different reaction velocities. Novák (1951and 1956) suggested a theory or hypothesis on the mode of action of JH on the basisand 1956) suggested a theory or hypothesis on the mode of action of JH on the basisof the gradient – factor as a factor conditioning the JH – independent growth of theof the gradient – factor as a factor conditioning the JH – independent growth of theimaginal parts of the body. According to this theory, JH produces its effect by takingimaginal parts of the body. According to this theory, JH produces its effect by takingthe place of the GF (Gradient factor) in those parts of the body which lose it in thethe place of the GF (Gradient factor) in those parts of the body which lose it in thecourse of development. Such parts are the larval parts of the body during larvalcourse of development. Such parts are the larval parts of the body during larvalSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect DevelopmentOO OOO2121OHOHHOOHOHHOO
  22. 22. development, the ovarian follicle in adult females, and a number of other tissues atdevelopment, the ovarian follicle in adult females, and a number of other tissues atparticular times during development. According to Novák (1954) and Sláma andparticular times during development. According to Novák (1954) and Sláma andWenig (1961), the effect of JH seems to depend on the conditioning of proteinWenig (1961), the effect of JH seems to depend on the conditioning of proteinsynthesis and other functions in the larval parts of the bodysynthesis and other functions in the larval parts of the body Fig. (6)Fig. (6)..The series of successive moulting processes subdivides the post – embryonicThe series of successive moulting processes subdivides the post – embryonicdevelopment in insects into several intermoult periods, or instars, during which (butdevelopment in insects into several intermoult periods, or instars, during which (butnot at any other time) growth and morphogenesis are possible. This cyclical eventnot at any other time) growth and morphogenesis are possible. This cyclical eventrepeated in each of the instars, which are strictly inter – related, are induced andrepeated in each of the instars, which are strictly inter – related, are induced andcontrolled by the three metamorphosis hormones; JH is one of them. Thus, insect’scontrolled by the three metamorphosis hormones; JH is one of them. Thus, insect’sdevelopment which includes both growth and morphogenesis is complicateddevelopment which includes both growth and morphogenesis is complicated Fig. (7)Fig. (7)..Long.Long. Cap.Cap. Cap.Cap. c.g.c.g. f.g.f.g.Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2222
  23. 23. RelativeRelativeIncreaseIncrease 11stst22ndnd33rdrd44thth55ththOO Larval InstarsLarval InstarsFig. (6): - Growth of the corpora allata compared with otherparts of the body during the 5thlarval instar of Bombyx mori[[Abscissa –Abscissa – Laval instars,Laval instars, Ordinate –Ordinate – Relative increase.Relative increase.f.g. = Frontal Ganglion,f.g. = Frontal Ganglion, c.g. = Cerebral Ganglion,c.g. = Cerebral Ganglion, Cap = Breadth of the Head,Cap = Breadth of the Head,Cap = Height of the Head,Cap = Height of the Head, Long = length of the BodyLong = length of the Body (Novák, 1954)(Novák, 1954)]]Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2323
  24. 24. Fig. (7): -Fig. (7): - Schematic representation of juvenile hormone (JH) and ecdysteroid titers duringSchematic representation of juvenile hormone (JH) and ecdysteroid titers duringdevelopment in Hemimetabola (development in Hemimetabola (Nauphoeta cineraNauphoeta cinera) and Holometabola () and Holometabola (Manduca sextaManduca sexta), and various), and variousevents that are caused by each hormone. All of the events in Holometabola are results from studies ofevents that are caused by each hormone. All of the events in Holometabola are results from studies ofbothboth Mamestra brassicaeMamestra brassicae andand M. sextaM. sexta. The horizontal black bars indicate the critical periods of JH. The horizontal black bars indicate the critical periods of JHfor commitments.for commitments. 20E =20E = 20 – Hydroxyecdysone;20 – Hydroxyecdysone; PTGPTG = Prothoracic gland;= Prothoracic gland;PTTHPTTH = Prothoracicotropic hormone;= Prothoracicotropic hormone; HCSHCS = Head capsule slippage= Head capsule slippage [Lanzrein et al. (1985)][Lanzrein et al. (1985)]Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2424
  25. 25. Actions of Juvenile Hormones on Endocrine SystemsActions of Juvenile Hormones on Endocrine SystemsJH not only modulates Ecdysone action on various tissues, but also affects theJH not only modulates Ecdysone action on various tissues, but also affects theactivities of other endocrine organs that are responsible for moulting andactivities of other endocrine organs that are responsible for moulting andmetamorphosis – in particular, the brain and the prothoracic gland.metamorphosis – in particular, the brain and the prothoracic gland.Larval MoultLarval MoultThe prolonged high JH titer seen during the penultimate larval instar is necessary toThe prolonged high JH titer seen during the penultimate larval instar is necessary tocause an increase in Ecdysteroid titer at a proper time in both Hemimetabolouscause an increase in Ecdysteroid titer at a proper time in both Hemimetabolous((Rhodnius prolixusRhodnius prolixus) and Holometabolous () and Holometabolous (MamestraMamestra andand ManducaManduca) insects. When JH) insects. When JHis removed by allatectomy, the large moulting surges of Ecdysteroid are drasticallyis removed by allatectomy, the large moulting surges of Ecdysteroid are drasticallydepressed, but the application of JH restores these surges. Indepressed, but the application of JH restores these surges. In MamestraMamestra, JH apparently, JH apparentlyactivates the brain to synthesize and / or release PTTH, which then stimulatesactivates the brain to synthesize and / or release PTTH, which then stimulatesEcdysteroid synthesis and release by the prothoracic glands.Ecdysteroid synthesis and release by the prothoracic glands.Larval – Pupal CommitmentLarval – Pupal CommitmentAfter the last larval ecdysis, the nature of the brain and prothoracic glands changesAfter the last larval ecdysis, the nature of the brain and prothoracic glands changesdramatically. During the feeding stage indramatically. During the feeding stage in ManducaManduca, the secretion of PTTH is strongly, the secretion of PTTH is stronglyinhibited by JH and growth continues if JH is present. Therefore, the decline of JH isinhibited by JH and growth continues if JH is present. Therefore, the decline of JH isimportant for the brain to release PTTH, which is responsible for the commitmentimportant for the brain to release PTTH, which is responsible for the commitmentpeak of ecdysteroid. The commitment peak does not appear until JH disappearspeak of ecdysteroid. The commitment peak does not appear until JH disappearscompletely. The signal for the decline of JH depends on the weight of the larvae, butcompletely. The signal for the decline of JH depends on the weight of the larvae, butthe means of recognition of the critical weight is unknown. After exposure of thethe means of recognition of the critical weight is unknown. After exposure of thecommitment peak of ecdysteroid, the responsiveness of prothoracic glands to JHcommitment peak of ecdysteroid, the responsiveness of prothoracic glands to JHdramatically changes indramatically changes in MamestraMamestra,, ManducaManduca andand Spodoptera littoralisSpodoptera littoralis. The. Theprothoracic glands before this exposure are inhibited by JH (larval type). Inprothoracic glands before this exposure are inhibited by JH (larval type). InMamestraMamestra, this transformation is caused by PTTH, which is responsible for the, this transformation is caused by PTTH, which is responsible for thecommitment peak and / or α – ecdysone from the prothoracic glands in the absence ofcommitment peak and / or α – ecdysone from the prothoracic glands in the absence ofJH. Unlike PTTH, the stimulatory action of JH on prothoracic glands appears to beJH. Unlike PTTH, the stimulatory action of JH on prothoracic glands appears to beSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2525
  26. 26. indirect. Inindirect. In ManducaManduca, JH causes the fat body to produce a haemolymph protein that, JH causes the fat body to produce a haemolymph protein thatenhances the production of ecdysteroids by the prothoracic glands.enhances the production of ecdysteroids by the prothoracic glands.Pupal MoultPupal MoultDuring the pupal moult, JH plays an important role not only for normal pupation butDuring the pupal moult, JH plays an important role not only for normal pupation butalso for the timing of pupation. The removal of this JH by allatectomy delays pupalalso for the timing of pupation. The removal of this JH by allatectomy delays pupalecdysis by a day or so in bothecdysis by a day or so in both MamestraMamestra andand ManducaManduca. Because the moulting peak. Because the moulting peakecdysteroid is also delayed under these conditions, the reappearance of JH at this timeecdysteroid is also delayed under these conditions, the reappearance of JH at this timeis likely important in conjunction with environmental signals that stimulate PTTHis likely important in conjunction with environmental signals that stimulate PTTHrelease.release.Roles of Juvenile Hormones in embryonic developmentRoles of Juvenile Hormones in embryonic developmentBoth ecdysteroids and JH are found in freshly laid eggs in the locust,Both ecdysteroids and JH are found in freshly laid eggs in the locust, LocustaLocustamigratoriamigratoria. The ecdysteroids are inactive conjugates; at times corresponding to the. The ecdysteroids are inactive conjugates; at times corresponding to theearly embryonic moults, these inactive conjugates are converted to 20E and otherearly embryonic moults, these inactive conjugates are converted to 20E and othermetabolites. The later ecdysteroid surges are likely a result of the prothoracic glandsmetabolites. The later ecdysteroid surges are likely a result of the prothoracic glandsof the embryo. The JH is wiped out by the JH esterases that appear with the onset ofof the embryo. The JH is wiped out by the JH esterases that appear with the onset ofthe embryonic development, and then JH reappears late during embryogenesis, whenthe embryonic development, and then JH reappears late during embryogenesis, whenit is secreted by the embryonic corpora allata. Init is secreted by the embryonic corpora allata. In NauphoetaNauphoeta, two surges of JH appear, two surges of JH appearshortly after dorsal closure. JH mimetics are applied to insect eggs during earlyshortly after dorsal closure. JH mimetics are applied to insect eggs during earlyembryogenesis to cause disruption of blastokinesis (the movement of the embryoembryogenesis to cause disruption of blastokinesis (the movement of the embryowithin the egg, so that its dorsal surface is towards the egg shell, known aswithin the egg, so that its dorsal surface is towards the egg shell, known asKatatrepsis) and often cause defects in dorsal closure. In the Hemimetabola, such asKatatrepsis) and often cause defects in dorsal closure. In the Hemimetabola, such asin the Locust, the presence of JH at the time of Katatrepsis, when JH is not normallyin the Locust, the presence of JH at the time of Katatrepsis, when JH is not normallypresent, also causes premature termination of patterning, suppression of growth, andpresent, also causes premature termination of patterning, suppression of growth, andprecocious differentiation of the nymphal stage. In Holometabola, as exemplified byprecocious differentiation of the nymphal stage. In Holometabola, as exemplified byLepidopterans, despite the effect of JH on blastokinesis, there is little effect on growthLepidopterans, despite the effect of JH on blastokinesis, there is little effect on growthand differentiation. This lack of effect of applied JH is thought to be due to the earlierand differentiation. This lack of effect of applied JH is thought to be due to the earlierSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2626
  27. 27. appearance of JH and other considerations have led Truman and Riddiford toappearance of JH and other considerations have led Truman and Riddiford tohypothesize that during the evolution of complete metamorphosis, the embryos ofhypothesize that during the evolution of complete metamorphosis, the embryos ofholometabolous insects showed advancement in the timing of JH secretion by theholometabolous insects showed advancement in the timing of JH secretion by theembryonic corpora allata. The resultant alteration in tissue patterning and precociousembryonic corpora allata. The resultant alteration in tissue patterning and precociousdifferentiation was then important for the evolution of the novel from the larva.differentiation was then important for the evolution of the novel from the larva.DiapauseDiapauseMany insects enter diapause (cease of normal progression of growth) at differentMany insects enter diapause (cease of normal progression of growth) at differentstages and it is triggered by environmental cues such as the temperature, day length,stages and it is triggered by environmental cues such as the temperature, day length,and humidity. Usually, diapausing insects differ from non – diapausing individualsand humidity. Usually, diapausing insects differ from non – diapausing individualsfrom the physiological and biochemical point of view. The programming of diapausefrom the physiological and biochemical point of view. The programming of diapauseis also under the control of hormones. Embryonic diapause inis also under the control of hormones. Embryonic diapause in BombyxBombyx is induced by ais induced by asuboesophageal ganglion diapause hormone that acts on the ovarioles of femalessuboesophageal ganglion diapause hormone that acts on the ovarioles of femalesduring egg maturation, and the females lay diapausing eggs therefore. Pupal diapauseduring egg maturation, and the females lay diapausing eggs therefore. Pupal diapauseis caused by arrest of PTTH release, so that the prothoracic glands are not stimulated.is caused by arrest of PTTH release, so that the prothoracic glands are not stimulated.JH is a key player in larval and adult diapause. Adult diapause is characterized by theJH is a key player in larval and adult diapause. Adult diapause is characterized by thehalt of reproduction and is basically due to the cessation of secretion of JH by thehalt of reproduction and is basically due to the cessation of secretion of JH by thecorpora allata. Diapause in last – instar Lepidopteran larvae has been well – studied.corpora allata. Diapause in last – instar Lepidopteran larvae has been well – studied.In both the rice Stem – borer,In both the rice Stem – borer, Chilo suppressalisChilo suppressalis, and the South Western Corn – borer,, and the South Western Corn – borer,Diatraea grandiosellaDiatraea grandiosella, the JH titer in the haemolymph is high during the diapause that, the JH titer in the haemolymph is high during the diapause thatnot only induces diapause but also maintains its status. A high JH titer also inducesnot only induces diapause but also maintains its status. A high JH titer also inducesthe prepupal diapause in the slug moth,the prepupal diapause in the slug moth, Monema flavescensMonema flavescens. Apart from that, there are. Apart from that, there areso many insects in the world, where larval diapause can be artificially induced by theso many insects in the world, where larval diapause can be artificially induced by theapplication of JH or even by Juvenoids also.application of JH or even by Juvenoids also.Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2727
  28. 28. Molecular Actions of Juvenile HormonesMolecular Actions of Juvenile HormonesVarious authors have attempted to explain the mode of JH at the molecular level. InVarious authors have attempted to explain the mode of JH at the molecular level. Inaddition to the hypothesis by Wigglesworth of the existence of two alternativeaddition to the hypothesis by Wigglesworth of the existence of two alternativeenzyme systems (larval and imaginal), Williams (1961) concluded that JH ‘blocks theenzyme systems (larval and imaginal), Williams (1961) concluded that JH ‘blocks theflow of fresh genetic information from nucleus to cytoplasm’. JH could do this byflow of fresh genetic information from nucleus to cytoplasm’. JH could do this byaffecting one or more possible feedback systems concerned with the repression ofaffecting one or more possible feedback systems concerned with the repression ofspecific regulators or some other link in the chain of protein synthesis. Clarke andspecific regulators or some other link in the chain of protein synthesis. Clarke andBaldwin (1960) considered the possibility that JH controls ATP synthesis by acting oBaldwin (1960) considered the possibility that JH controls ATP synthesis by acting othe mitochondrial cytochrome system. On the basis of the experiments on the flightthe mitochondrial cytochrome system. On the basis of the experiments on the flightmusculature of the Colorado Beetle, Stegwee (1960) suggested that the hormonemusculature of the Colorado Beetle, Stegwee (1960) suggested that the hormonemight stimulate succinate oxidation and that the site of stimulation was that part of themight stimulate succinate oxidation and that the site of stimulation was that part of therespiratory chain between succinate and cytochrome – c. Gilbert (1964) concludedrespiratory chain between succinate and cytochrome – c. Gilbert (1964) concludedthat the site of action of JH might be the nucleus, where it influenced chromosomalthat the site of action of JH might be the nucleus, where it influenced chromosomalmetabolism and thus affected the specificity of the protein synthesis. Ilan et. al. (1970)metabolism and thus affected the specificity of the protein synthesis. Ilan et. al. (1970)suggested that JH might control gene expression at the translational level. Schmialeksuggested that JH might control gene expression at the translational level. Schmialek(1972) had showed many chemical evidences in support of the explanation of JH(1972) had showed many chemical evidences in support of the explanation of JHaction, i.e., the coupling of DNA molecules with certain isoprenoid compounds,action, i.e., the coupling of DNA molecules with certain isoprenoid compounds,which include many of the effective JH analogues (McMullen, 1961). Williams andwhich include many of the effective JH analogues (McMullen, 1961). Williams andKafatos (1971 and 1973) formulated a new version of the ‘repression’ theory of JHKafatos (1971 and 1973) formulated a new version of the ‘repression’ theory of JHaction. Following the ‘depression’ theory of Jacob and Monod, they consider that JHaction. Following the ‘depression’ theory of Jacob and Monod, they consider that JHplays the role of an activator (= co – repressor) of the pupal and adult ‘master – genes’plays the role of an activator (= co – repressor) of the pupal and adult ‘master – genes’determining pupal and imaginal differentiation. The corresponding repressors aredetermining pupal and imaginal differentiation. The corresponding repressors areactive only in presence of JH.active only in presence of JH.JH enters the larval epidermal cell inJH enters the larval epidermal cell in ManducaManduca and one – third goes to the nucleusand one – third goes to the nucleusphotoaffinity – labeled JH I, JH II and methoprene (a JH mimic) bind to a 29KDaphotoaffinity – labeled JH I, JH II and methoprene (a JH mimic) bind to a 29KDaprotein that is found in the larval epidermis. Once it was thought that this protein is aprotein that is found in the larval epidermis. Once it was thought that this protein is aJH receptor, but further studies have shown only a low – affinity binding protein.JH receptor, but further studies have shown only a low – affinity binding protein.Recently, it has been reported thatRecently, it has been reported that DrosophilaDrosophila ultraspiracle protein (USP) binds JH IIIultraspiracle protein (USP) binds JH IIISynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2828
  29. 29. and JH III bisepoxide with low affinity (about 4 X 10and JH III bisepoxide with low affinity (about 4 X 10 -7-7µ). JH III and methopreneµ). JH III and methoprenecannot replace the bacterial phospholipid found in the ligand – binding pocket ofcannot replace the bacterial phospholipid found in the ligand – binding pocket ofrecombinant USP, but JH I acid is predicted to fit into this pocket. However, norecombinant USP, but JH I acid is predicted to fit into this pocket. However, nofunctional studies of the role of USP as a JH receptor have been reported. There are afunctional studies of the role of USP as a JH receptor have been reported. There are anumber of reports regarding JH – binding proteins. Among them, most interesting arenumber of reports regarding JH – binding proteins. Among them, most interesting arethe methoprene – tolerant (Met) gene inthe methoprene – tolerant (Met) gene in DrosophilaDrosophila mutants, that have an intracellularmutants, that have an intracellularJH – binding protein with reduced JH –JH – binding protein with reduced JH – binding activity. The Met protein is found inbinding activity. The Met protein is found inthe nucleus and has a high degree of similarity to the basic helix – loop – helix Per,the nucleus and has a high degree of similarity to the basic helix – loop – helix Per,Arnt and Sim (PAS) domain family members. How this is related to JH action is stillArnt and Sim (PAS) domain family members. How this is related to JH action is stillnot known fully. Null mutants show no defect in development, but have delayed andnot known fully. Null mutants show no defect in development, but have delayed andreduced vitellogenesis. Therefore, a JH receptor for insect development is still elusive.reduced vitellogenesis. Therefore, a JH receptor for insect development is still elusive.Regulation of the Ecdysone – Induced TranscriptionRegulation of the Ecdysone – Induced TranscriptionFactor Cascade (ETFC)Factor Cascade (ETFC)Most of the events caused by 20E are through the control of the Ecdysone ReceptorMost of the events caused by 20E are through the control of the Ecdysone Receptor(EcR), but EcR is an inactive receptor and it needs to partner with Ultraspiracle(EcR), but EcR is an inactive receptor and it needs to partner with Ultraspiracleprotein to be functional. 20 – Hydroxy – Ecdysone enters the cells and then theprotein to be functional. 20 – Hydroxy – Ecdysone enters the cells and then thenucleus, where EcR and USP are bound to the DNA. Once 20E binds to EcR, thenucleus, where EcR and USP are bound to the DNA. Once 20E binds to EcR, the20E / EcR / USP complex directly activates the early gene (e.g. E75 and BR – C), the20E / EcR / USP complex directly activates the early gene (e.g. E75 and BR – C), theprotein products of which in turn activate the late tissue specific genes (e.g. L71 in theprotein products of which in turn activate the late tissue specific genes (e.g. L71 in thesalivary gland) and inhibit the early genes. 2 – 3 isoforms of EcR and USP are knownsalivary gland) and inhibit the early genes. 2 – 3 isoforms of EcR and USP are knownfrom various insects, and the receptor levels fluctuate with development. The primaryfrom various insects, and the receptor levels fluctuate with development. The primaryrole of JH in morphogenesis is to modulate the ecdysone action, and JH alsorole of JH in morphogenesis is to modulate the ecdysone action, and JH alsomodulates the ecdysone – inducible EcR and USP expression. Expression of both EcRmodulates the ecdysone – inducible EcR and USP expression. Expression of both EcRand USP is up – regulated by 20E in a complex fashion. In theand USP is up – regulated by 20E in a complex fashion. In the ManducaManduca epidermis,epidermis,the expression of all of the EcR (EcR – A and EcR – B1) and USP (USP – 1 and USPthe expression of all of the EcR (EcR – A and EcR – B1) and USP (USP – 1 and USP– 2) isoforms is induced by 20E, but JH prevents this action. The one exception is– 2) isoforms is induced by 20E, but JH prevents this action. The one exception isSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 2929
  30. 30. USP – 2, which is unaffected by JH. JH is also known to prolong the half – life ofUSP – 2, which is unaffected by JH. JH is also known to prolong the half – life ofboth EcR – A and EcR – B1 proteins.both EcR – A and EcR – B1 proteins.Regulation of Cuticular MelanizationRegulation of Cuticular MelanizationLarval pigmentation is under the control of JH in many insects, but there are not manyLarval pigmentation is under the control of JH in many insects, but there are not manystudies at the molecular level. Normally,studies at the molecular level. Normally, ManducaManduca larvae have a transparent cuticlelarvae have a transparent cuticlewith black markings. Yet when JH is removed by allatectomy about 30 hrs. before thewith black markings. Yet when JH is removed by allatectomy about 30 hrs. before thelast larval ecdysis, cuticular melanization occurs in the newly synthesized Vlast larval ecdysis, cuticular melanization occurs in the newly synthesized Vththinstarinstarlarval cuticle and can be prevented by application of JHlarval cuticle and can be prevented by application of JH Fig. (7)Fig. (7)..CUTICULAR MELANIZATIONCUTICULAR MELANIZATION ------JHJHDDCDDC Granular POGranular PODopaDopa Dopamine MelaninDopamine MelaninCOMMITMENTCOMMITMENT --------JHJHE75AE75ABR – CBR – C BR - CBR - CBR – CBR – C BR - CBR - CFig. (8): - Models for molecular actions of juvenile hormones (JH)Fig. (8): - Models for molecular actions of juvenile hormones (JH)[DDC = Dopa decarboxylase; PO = Phenoloxidase; BR – C = Broad Complex;[DDC = Dopa decarboxylase; PO = Phenoloxidase; BR – C = Broad Complex;= Induction; = Inhibition]= Induction; = Inhibition]Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 3030Larva Pupa Adult
  31. 31. The melanin is dopamine – melanin and found in granules deposited to the cuticle.The melanin is dopamine – melanin and found in granules deposited to the cuticle.Accordingly, Dopa decarboxylase (DDC) [converts Dopa to Dopamine] and granularAccordingly, Dopa decarboxylase (DDC) [converts Dopa to Dopamine] and granularphenoloxidase (PO) [oxidizes Dopamine in the first step of the oxidative path tophenoloxidase (PO) [oxidizes Dopamine in the first step of the oxidative path tomelanin] are crucial enzymes for this process. In allatectomized melanizing larvae, themelanin] are crucial enzymes for this process. In allatectomized melanizing larvae, theabdominal epidermis produces a granular pro – PO that is incorporated to the newabdominal epidermis produces a granular pro – PO that is incorporated to the newcuticle in the premelanin granules. The pro – PO is later activated by the decline ofcuticle in the premelanin granules. The pro – PO is later activated by the decline ofecdysteroid titer. The application of JH 25 to 30 hrs. before ecdysis completelyecdysteroid titer. The application of JH 25 to 30 hrs. before ecdysis completelyprevents the production of this enzymeprevents the production of this enzyme Fig. (8)Fig. (8). DDC is essential for not only. DDC is essential for not onlymelanization but also for cuticular sclerotization, and its activity and its mRNAmelanization but also for cuticular sclerotization, and its activity and its mRNAincreases titer. In allatectomized larvae, the levels are two folds higher than those inincreases titer. In allatectomized larvae, the levels are two folds higher than those innon – melanizing normal larvaenon – melanizing normal larvae Fig. (8)Fig. (8). The excess dopamine is incorporated to the. The excess dopamine is incorporated to thegranules deposited in the cuticle, where activated granular PO is present, so thatgranules deposited in the cuticle, where activated granular PO is present, so thatmelanization occurs within the granules. The action of JH on DDC gene expression ismelanization occurs within the granules. The action of JH on DDC gene expression isthus to modify the amount of gene expression, as is also seen in E75A, rather than thethus to modify the amount of gene expression, as is also seen in E75A, rather than thesuppression of new gene expression, as seen in granular PO. The mode of action ofsuppression of new gene expression, as seen in granular PO. The mode of action ofJH in both cases is still unknown.JH in both cases is still unknown.Larval Pupal CommitmentLarval Pupal CommitmentIn the ecdysone cascade, in addition to EcR and USP, JH affects the expression of aIn the ecdysone cascade, in addition to EcR and USP, JH affects the expression of afew other transcription factors. Infew other transcription factors. In ManducaManduca, studies of the metamorphic role of these, studies of the metamorphic role of thesefactors show that JH enhances the expression of one of the 20E – inducedfactors show that JH enhances the expression of one of the 20E – inducedtranscription factors, E75A, in larval epidermis, where it prevents pupal commitmenttranscription factors, E75A, in larval epidermis, where it prevents pupal commitmentof the epidermis, suggesting that a high titer of E75A is important for maintenance ofof the epidermis, suggesting that a high titer of E75A is important for maintenance ofthe larval statethe larval state Fig. (8)Fig. (8). Another 20E – induced transcription factor, BR – C, is. Another 20E – induced transcription factor, BR – C, isexpressed only from the time of pupal commitment through the time of pupation inexpressed only from the time of pupal commitment through the time of pupation inbothboth ManducaManduca andand DrosophilaDrosophila. In. In ManducaManduca, the appearance of BR – C protein, the appearance of BR – C proteincorrelates with pupal commitment of the abdominal epidermis on day 3 of the finalcorrelates with pupal commitment of the abdominal epidermis on day 3 of the finallarval instar, and the prevention of pupal commitment by JH prevents BR – Clarval instar, and the prevention of pupal commitment by JH prevents BR – Cexpression bothexpression both inin vivovivo andand inin vitrovitro Fig. (8)Fig. (8). Expression of BR – C in the abdominal. Expression of BR – C in the abdominalSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 3131
  32. 32. epidermis occurs in a strict spatial pattern that coincides with the loss of theepidermis occurs in a strict spatial pattern that coincides with the loss of thesensitivity to JH. Furthermore, once epidermis is exposed to 20E for 6 hrs, at whichsensitivity to JH. Furthermore, once epidermis is exposed to 20E for 6 hrs, at whichtime BR – C mRNA is first detectable, JH can no longer prevent BR – C expression.time BR – C mRNA is first detectable, JH can no longer prevent BR – C expression.Similarly, JH can not prevent the pupal commitment once the cells are exposed toSimilarly, JH can not prevent the pupal commitment once the cells are exposed to20E, in the absence of JH, for more than 6 hrs. The appearance of BR – C mRNA in20E, in the absence of JH, for more than 6 hrs. The appearance of BR – C mRNA inwing discs also correlates with their pupal commitment. Therefore, BR – C expressionwing discs also correlates with their pupal commitment. Therefore, BR – C expressionis one of the first molecular events underlying pupal commitment of both abdominalis one of the first molecular events underlying pupal commitment of both abdominalepidermis and wing discs. In addition,epidermis and wing discs. In addition, DrosophilaDrosophila mutants that lack BR – C entirelymutants that lack BR – C entirelydevelop normally until metamorphosis, but die before pupation. These observationsdevelop normally until metamorphosis, but die before pupation. These observationssuggest that BR – C is a key factor for metamorphosis.suggest that BR – C is a key factor for metamorphosis.A recent breakthrough on the molecular mechanism of pupal commitment hasA recent breakthrough on the molecular mechanism of pupal commitment hasbeen reported by Zhou and Riddiford (2002), who clearly showed inbeen reported by Zhou and Riddiford (2002), who clearly showed in ManducaManduca and inand inDrosophilaDrosophila that BR – C is a pupal – specifying transcription factorthat BR – C is a pupal – specifying transcription factor Fig. (8)Fig. (8). Normally. NormallyBR – C is present during pupal cuticle formation but is not present during the adultBR – C is present during pupal cuticle formation but is not present during the adultmoult. When JH is given just before or after pupal ecdysis inmoult. When JH is given just before or after pupal ecdysis in ManducaManduca, BR – C, BR – CmRNA can be also inducedmRNA can be also induced inin vitrovitro by exposing the pupal wing to 20E in the presenceby exposing the pupal wing to 20E in the presenceof JH. Inof JH. In DrosophilaDrosophila, the application of JH at pupariation causes the formation of a, the application of JH at pupariation causes the formation of a“pharate adult” with a normal adult head and thorax, but a pupal – like abdomen. In“pharate adult” with a normal adult head and thorax, but a pupal – like abdomen. Inthese JH – treated insects, BR – C mRNA is re – expressed during adult developmentthese JH – treated insects, BR – C mRNA is re – expressed during adult developmentin the abdomen, but not in the thorax and the head. Moreover, pupal gene is or pupalin the abdomen, but not in the thorax and the head. Moreover, pupal gene is or pupalcuticle genes are re – expressed and an adult cuticle gene is suppressed in the JH –cuticle genes are re – expressed and an adult cuticle gene is suppressed in the JH –treated abdomen. These findings show that the abdominal cells are making a secondtreated abdomen. These findings show that the abdominal cells are making a secondpupal cuticle. The use of transgenicpupal cuticle. The use of transgenic DrosophilaDrosophila carrying the various BR – C isoformscarrying the various BR – C isoformsunder a heat – shock promoter allows determination of the effects of misexpression ofunder a heat – shock promoter allows determination of the effects of misexpression ofeach of the four isoforms (Z1 – Z4) on pupal cuticle production. Expression of the Z1each of the four isoforms (Z1 – Z4) on pupal cuticle production. Expression of the Z1isoform at the onset of cuticle production induces re – expression of an adult cuticleisoform at the onset of cuticle production induces re – expression of an adult cuticlegene, causing the deposition of a second pupal cuticle. Unlike the JH – treated flies,gene, causing the deposition of a second pupal cuticle. Unlike the JH – treated flies,this induction of a new pupal cuticle occurs in the head and thorax as well as in thethis induction of a new pupal cuticle occurs in the head and thorax as well as in theabdomen. Interestingly, misexpression of the Z1 isoform during the second larvalabdomen. Interestingly, misexpression of the Z1 isoform during the second larvalSynthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 3232

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