Biochemical changes during oogenesis

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Biochemical changes during oogenesis

  1. 1. BIOCHEMICAL CHANGES DURING OOGENESIS GOMATHI.M MSc ZOOLOGY BHARATHIAR UNIVERSITY 1
  2. 2. OBJECTIVES • • • • INTRODUCTION OOGENESIS PROCESS OF OOGENESIS BIOCHEMICAL CHANGES DURING OOGENESIS 1. Changes during proliferative phase 2. Changes during Growth phase 3. Changes during Maturation phase • SIGNIFICANCE OF OOGENESIS • CONCLUSION 2
  3. 3. REPRODUCTION • What type of cell division takes place? • MEIOSIS + MITOSIS 3
  4. 4. GAMETOGENESIS • GAMETES :Oocytes and Spermatozoa (n) OOGENESIS SPERMATOGENESIS 4
  5. 5. OOGENESIS • Production and maturing of ovum. • The differentiation of the ovum • “CREATION OF HAPLOID EGG CELLS USING MEIOSIS” 5
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  7. 7. PRIMORDIAL GERM CELLS (PGCs) GAMETES GAMETOGENESIS: OOGENESIS DURING 2ND WEEK OF EMBRYO 4TH WEEK 5TH WEEK PGC FORMED IN EPIBLAST PGC BEGINS TO MIGRATE FROM THE YOLK SAC MIGRATION ENDS IN DEVELOPING GONADS (OVARY) DIFFERENTIATE INTO OOGONIA - 7 MILLION CELL DEATH BEGINS -MAJORITY OF OOGONIA DEGENERATED 6TH WEEK 7TH WEEK REMAINING PRIMARY OOCYTES HAVE ENTERED PROPHASE OF MEIOSIS I – DIPLOTENE STAGE (RESTING PHASE) • Oogonia divide rapidly from the second to the seventh month of gestation to form roughly 7 million germ cells. After the seventh month number of germ cells drops precipitously. AT BIRTH BEGINNING OF PUBERTY TILL 50 YEARS (MENOPAUSE) 2 MILLION PRIMARY OOCYTES 400,000 500 ONLY OVULATED 7
  8. 8. • Oogonia divide rapidly from the second to the seventh month of gestation to form roughly 7 million germ cells. After the seventh month number of germ cells drops precipitously. 8
  9. 9. PROCESS OF OOGENESIS MULTIPLICATION PHASE GROWTH PHASE MATURATION PHASE 9
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  11. 11. BIOCHEMICAL CHANGES DURING OOGENESIS • • • • • NUCLEUS CYTOPLASM RNA YOLK – PROTEINS HORMONES- GONADOTROPIN HORMONES , OVARIAN HORMONES 11
  12. 12. BIOCHEMICAL CHANGES • Gametes formed by oogenesis contains all the materials needed to initiate and maintain metabolism and development. 1. 2. 3. 4. 5. 6. 7. 8. 9. Form haploid nucleus, All the organelles involved in fertilization have to be constructed, All the mRNAs & proteins have to positioned properly in the oocyte, All the membrane proteins involved in coordinating the interactions with sperm have to be synthesized and in place, The accumulated material in the oocyte cytoplasm includes energy sources and energy –producing organelles(yolk & mitochondria) The enzymes and precursors for DNA, RNA and protein synthesis, Stored messenger RNAs, Structural proteins, Morphogenetic regulatory factors that control early embryogenesis 12
  13. 13. CELLULAR COMPONENTS STORED IN THE MATURE OOCYTE OF XENOPUS LAEVIS COMPONENT MITOCHONDRIA APPROXIMATE EXCESS OVER AMOUNT IN LARVAL CELLS 100,000 RNA POLYMERASES 60,000 -100,000 DNA POLYMERASES 100,000 RIBOSOMES 200,000 TRNA 10,000 HISTONES 15,000 DEOXYRIBONUCLEOSIDE TRIPHOSPHATES 2,500 13
  14. 14. • Oogenesis vary among species to species. • E.g. Sea urchin & Frogs - routinely produces hundreds or thousands of eggs at a time. • Humans and most mammals - only a few eggs are produced during the lifetime of an individual. Most of the biochemical changes takes place in the growth phase 14
  15. 15. 1) MULTIPLICATION PHASE MITOSIS MITOSIS • PGCs OOGONIA 1⁰ OOCYTE • No conspicious changes have been traced upto the formation of primary oocyte. 15
  16. 16. 2)GROWTH PHASE 1. Oocyte increases in size • Nutrients & other materials synthesized, then these substances accumulate in the cytoplasm. Young oocyte of frog - 50µ in diameter Mature oocyte of frog- 20-40 times larger. Hen’s oocyte- 200 times larger. Mouse oocyte- 43 times larger. 16
  17. 17. 2. Period of growth: Frog 3 years oogenesis – first 2 years size increase gradually then 3rd year accumulation of yolk increases its size. Human – 12 or 13 years 3. Stages of growth phase: i. Previtellogenesis (cytoplasmic & nuclear materials grow- no yolk synthesis) ii. Vitellogenesis (synthesis of yolk ) 17
  18. 18. PREVITELLOGENESIS VITELLOGENESIS • mRNA tRNA rRNA Nucleus increase in size Nucleoli increase in number Mitochondria increase in number Corticle granules in GB Follicle Cells/Nurse Cells YOLK FORMATION 18
  19. 19. CHANGES DURING PREVITELLOGENESIS • Nuclear sap produced in a large amount – nucleus increases its size = Germinal vesicle. 19
  20. 20. • Homologous chromosomes pair together. • Active mRNA synthesis – GENE TRANSCRIPTION IN AMPHIBIAN OOCYTES: • During the diplotene stage, certain chromosomes stretch out large loops of DNA, causing the chromosome to resemble a lamp brush. These lamp brush chromosomes can be revealed as the sites of RNA synthesis by in situ hybridization. 20
  21. 21. • Oocyte chromosomes can be incubated with a radioactive RNA probe, and autoradiography used to visualize the precise location where the gene is being transcribed. Figure shows diplotene chromosome I of the newt Triturus cristatus after incubation with radioactive histone mRNA.It is obvious that a histone gene (or set of histone genes) is located on one of these loops of the 21 Lampbrush chromosome (Old et al. 1977).
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  23. 23. VITELLOGENESIS • Liver produce inactive/precursor vitellogenin • Transported through blood to ovary enzymes protein kinase convert it into active vitellogenin- mitochondria 23
  24. 24. • The growing diplotene oocyte is actively transcribing the genes for zona pellucida proteins ZP1, ZP2, and ZP3. 24
  25. 25. MATURATION PHASE • The diploid primary oocyte reduced into haploid & form ovum. • 1st meiotic division – 1 polar body having small amount of cytoplasm - larger cytoplasm having cell is known as secondary oocyte. 2nd meiotic division – produce 3 polar bodies and a single ovum 25
  26. 26. • The time of maturation varies in different species. • It may occur after / before fertilization or at the time of fertilization. • Sea urchin – before • Vertebrates – after • Acidian – at time of fertilization 26
  27. 27. OOGENESIS IN MAMMALS 27
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  30. 30. HORMONAL CHANGES DURING OOGENESIS 30
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  33. 33.  FSH promotes the growth & development of oocyte  LH triggers ovulation  FSH, LH promote meiotic maturation division of oocyte and stimulate follicle cells to synthesis vitellogenin. 33
  34. 34. • During the process of oogenesis, oocytes of many animal species undergo meiotic arrest prior to the completion of chromosomal reduction and it is in this state that they undergo tremendous growth. The length of time that oocytes remain in this arrested state and the nature of the stimulus which reinitiates meiosis are species dependent 34
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  36. 36. SIGNIFICANCE OF OOGENESIS • WITHOUT OOGENESIS THERE IS NO FERTILIZATION, REPRODUCTION, LIFE….. 36
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  38. 38. REFERENCES 1. Scott F.Gilbert, 2009, Developmental Biology 8th edition, Sinauer Associates,inc.,Publishers,USA. 2. Berry Mitchell, Tam Sharma, 2005, “Embryology an illustrated color text 2nd edition, Churchill Livingstone Elsevier publishers, Pg: 1-10. 3. Mace Welene Vorlhac, Anne Villeneure, 2010, “Oogenesis, The Universal Process”, Wiley lackwell publishers, Pg: 38-41 4. Edwin F.Bartholonew, William C.Ober, Claire W.Garrison, Karhleen Welch, Talph T Hutchings, frederic H Matini, Judi.L.Nath, 2009, “Fundamentals fo Anatomy & Physiology” 8th edition, pearson, Benfamien cumming publication, Pg: 1061 – 1070. 5. Gary A. Jhibodeau, Kevin T.Patton, 2009, Anthong’s textbooks of Anatomy & Physiology 7th edition, moshy an Inprint & Elsevies publication, Pg: 941 – 945. 38
  39. 39. REFERENCES 6.http://www.endotext.org/female/female1/fe male1.htm 7.http://howmed.net/anatomy/embryology/oog enisis-and-ovarian-cycle/ 8.http://artificialinsemination.wordpress.com/a bout/reproductive-anatomy/ 9.http://www.womenshealthcare.org/articles/estrogen.html 39
  40. 40. REFERENCES • 8. http://buffonescience9.widispaces.com/UNIT +3-+cell+reproduction. • 9. http:///pc1.clpccd.cc.ea.us//pc/zingg/anat/ale cture/ach27flsldo11.htm. • 10. http://www.fastbleep.com/biologynotes/32/159/859. 40
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