Spermatogenic EpithelialCycle(SEC)ByFalana Benedict AbiolaB.Sc (Hons) Unilorin; M.Sc. (Anatomy) Ile-IfePractice Seminar 1Department of Anatomy, College ofMedicine of the University of Lagos,NigeriaMatriculation Number 109091016
Outline• Introduction to SEC• The cycle and wave• Selected Stages• Structure of the testes and spermatogenesis• Evolution of the study• Seminiferous epithelium• Conclusion• References
Introduction• Spermatogenic lineage development is acomplex process but occurs in an orderlymanner referred to as the spermatogenic cycle((Clermont 1972)• Proteins and mRNAs are exchanged viacytoplasmic bridges and may help incoordinating the synchronized development ofgerm cell clones.( Braun et al.,1989)
Introduction• Each stage is characterized by a combinationof different types of spermtogoonia,spermatocytes and spermatids thatsynchronously proceed through thespematogenic process.• The complete spermatogenic cycle in mousewas
SEC• Layers of germ cells all develop in acoordinated, repeating programme known asseminiferous epithelial cycle.• In rodents, successive stages are arranged incylindrical segments along the STs.
• Its existence been demonstrated in manyvertebrate species. (Kerr, 1995; Sharpe, 1994)• They are features of vertebrate spermatogenicorganization that reflect the need for a rigoroussperm production. (Timmons et al.,2002)Cycle and Wave
Cycle and Wave• Cycle of the seminiferous epithelium :– synchronous mitotic meiotic divisions– 6 stages in man– 4.6 cycle from sperm release (16 days per cycle)• Waves of the seminiferous epithelium :– in rodents and other mammals– no waves in human seminferous tubule
Stages• These are designated stages I-XIV of theseminiferous epithelial cycle in rat (Leblond andClermont,1952).• Twelve such stages (I-XII) have beendescribed in the mouse (Oakberg, 1965a)
Stages• Stage duration is precisely timed.• The complete spermatogenic cycle wasdetermined to be 8.6 days in the mouse (Okberg1956b) and 12.6 days in rats (Hilscher et al.,1969)
Stages in the indian gerbil field rat(Terata indica)• Four generations of A type, a single generationof intermediate(In) and two generations of Btype spermatogoonia are identified by Bilaspuri and Kaur(1994).
Stages in T.indica• Spermatocytes have been observed inprophase, metaphase, anaphase and telophase;in terms of size and morphology, the phases ofprophase could further be subdivided. (Bilaspuri and Kaur1994).
Stages in the Buffalo (BosBubalos)• Using H&E preparations the SEC in thebuffalo has been divided into 8 stages;1,2,3,4and 8 have been subdivided. Guraya and Bilaspuri (1976)
Stages in the Buffalo• The buffalo spermatogenesis is constituted by4.57 cycle of seminiferous epithelium whichresembles that of the bull. (Guraya and Bilaspuri 1976)
Spermatogenesis (I)• Spermatogonial phase :– type A dark (Ad) spermatogonia :• the stem cells of the seminiferous epithelium– type A pale (Ap) spermatogonia :• committed to differentiation– type B spermatogonia :• differentiated from type A spermatogonia• the last event in the spermatogonial phase
Spermatogenesis (II)• Spermatocyte phase : meiosis– primary spermatocyte : 4n• produced by type B spermatogonia• first meiotic division• homologous chromosomes crossing-over• give rise to secondary spermatocyte– secondary spermatocyte : 2n• second meiotic division• give rise to spermatid
Spermatid Phase (Spermiogenesis)• Golgi phase :– proacrosomal granules-acrosomal vesicle– axonemal complex : sperm tail• cap phase : acrosomal cap• acrosome phase :– manchette (flagellum development), nucleus condense• maturation phase :– residual body is pinched off and phagocytized by Sertolicells
Variation in Sperm Production• Testis Size• Efficiency of spermatogenesis– mitotic division– degeneration of germ cells• Length of spermatogenesis
Human Spermatozoon:• 60 um long, consist of a head & a tail.• Head: pear-shaped & flattened w/ a nuclear & aacrosome (contains hydrolytic enzyme important forfertilization).• Tail: 55um in length w/ a microtubular axoneme in thecore.Subdivided into 4 segments:(a)The neck, containing a centriole (connect)(b)The middle segment (5-7um), containing asheath of mitochondria (provide energy).(c)The principal segment (45um), containing afibrous sheath (support the tail).(d)The end piece (5-7um), containing amicrotubular axoneme.
Evolution of the study• The definition of stages of the cycle ofseminiferous epithelium in rats was madepossible by the work of (Leblond and Clermont (1952)• The existence of a wavy nature ofspermatogenic epithelium was discovered byPerey et al .,(1961)
Evolution of the study• Further more Huckins and Clermont(1968) reported theevolution of gonocytes in the rat testes duringlate embryonic and early post natal life.• Sertoli-germ cell communications networkwas reported to play a key role in regulatingSEC Jegou (1993)
Evolution of the study• The macro, micro and molecular research onspermatogenesis was undertaken by Kerr (1995) in aquest to understand its control.
Evidence of Expressed Proteins• Galectin family currently includes 10mammalian members (Cooper and Barondes, 1999), which areexpressed in many different embryonic tissuesand adult tissues where they may be foundeither in the intracellular or extracellularcompartments, or both (Harrison and Wilson 1992; Hughes, 1999)
Expressed Proteins• These proteins have been implicated in manydifferent biological processes, including cellrecognition (Puche et al.,1996), cell adhesion (Cooper et al.1991;Hadariet al. 2001; Kuwabara and Liu 1996), organization of extracellularmatrix (Hikita et al., 2000) and programmed cell death(Akahani et al., 2001; Perillo et al., 1995)
Galectin 1 expression in the developing testis.Timmons P M et al. Development 2002;129:635-647
Seminiferous epithelium(SE)• A complex and highly dynamic tissue.• Male reproductive success ultimately dependson the ability of this tissue to produceprodigious numbers of sperm consistency.
Seminiferous epithelium(SE)• Its organization into tubules serves providemaximum area for sperm production.• The structure of the epithelium and the preciseorchestration of spermatogenesis makes spermrelease regular.
Seminiferous epithelium• Developing cells gradually traverse theepithelium from the basement membrane tothe apical surface .• They are then released into the tubule lumenas spermatozoa.• Spermatogenesis progresses.
Seminiferous epithelium• The adult Seminiferous epithelium alwayscontains several layers of germ cells atdifferent stages of development.
Seminiferous epithelium• Stages of the seminiferous epithelial cycle insections of adult testes has been determined bylight microscopy ( leblond and Clermont, 1952; Parvinen, 1982;Russell et al.,1990)
Function:(l) Support & nourish spermatogenic cells;(2) Secrete fluid to help the sperm moving;(3) Phagocytize & digest the residual bodies(4) Synthesize & secrete ABP (androgen bindingprotein) which combines androgen inseminiferous tubule to stimulate spermatogenesis;(5) Form the blood-testis barrier: Tight junctionconstitute the main part (rest: B.M. & limitingmembrane). Function: separates germ cells fromimmune system & prevents auto-immunereaction.(6) Prevent some physical & chemical factors fromdamaging germ cells, e.g. radiation, bodytemperature, infection
Conclusion• The SEC is a conserved feature necessary forthe sustenance of fertility in Man.• Further studies on SEC in other Mammalswould shed more light on these complexphenomena.
References• Timmons, P.M., Rigby, P.W.J.,Poirier F.,(2002).Themurine sminifeous epithelial cycle is pre-figured inthe sertoli cells of the embryonic testis• Bilaspuri, G.S and Kaur, I (1994). Spermatogeniccells and stages of the seiniferous epithelial cycle inthe indian gerbil rat, Terata indica
References• Prince C.G and Loveland K.L (2000).Germ cellsuicide: New insights into apoptosis duringspermatogenesis. Bioessays 22, 423-430• Perey, B.,Clermont,Y., and leblond, C.(1961)Thewave of the spermatogenic epithelium in the rat.Am .J.of Anat.108, 47-48• Leblond, C.P andClermont,Y.(1952).Definition of thestages of the cycle of seminiferous epithelium in therat.AnnNew yorkacad.sci.55, 548-573
References• Kiers zemembaum, A.L. (2001). Apoptosis duringspermatogenesis: The trills of being alive. Mol.Reprod. Dev. 58, 1-3• Kerr, J.B.(1995)Macro, microand molecular researchon spermatogenesis: quest to understandits control.Microsc.Res.Tech.32, 364-384
References• Jegou, B .(1993).The sertoli-germ cellcommunications network in mammals.Intrev.Cytol.14725-96• Hughes, R.C.(1999). Secretion of galectin family ofmammalian carbohydrate –binding proteins. Biochimbiophys.Acta.1473, 172-185• Huckins, C and Clermont, Y.(1968).Evolution ofgonocytes in the rat testes during late embryonic andearly post-natal life . Arch.Anat.Histol.Embryol.51-341-354
References• Hikita C..,Vijayakumar.,S.,Takito.,J.,Erdjument-Bromage,H.,Tempest, P.,and Al-awquati, Q.(2000).Induction of terminal differentiation onin epithelialcells requires polymerization ofhensin by galectin 3..J.Cell Biol.151, 1235-1246• Eddy, E.M., and O’Brien, D.A.,(1998).Geneexpression durin mammalian meiosis.Curr.top.Dev.Biol37,141-200
References• Enders, G.C.(1993).Sertoli-sertoli and sertoli-germ cell communication. In the sertoli cell.(ed L.D. Russel and M.D.Griswold), pp.447-460. Clearwater, FL. Cache RiverPress• Clermont, Y and Perey, B.(1957).Quantitativestudy of the cell populationof the seminiferoustubules in immature rats.Am. J. Anat100, 241-268