Bi-potent Gonads. Sex Determination

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2 יצירת הגונדות

3 Primordial Germ Cells (PGCs) Somatic cells Genital ridge Bi-potent Gonads Sex Determination Testis and Sperm Ovary and Oocyte

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6 Migration of Primordial Germ Cells in the Chick Embryo

7 The Germinal Crescent of the Chick Embryo

8 Blood system of the developing chick embryo

9 Migration of Primordial Germ Cells in the Chick Embryo

10 Specification of Mammalian Primordial Germ Cells

11 Pathway for the Migration of Mammalian Primordial Germ Cells

12 Expression of Oct4 mrna correlates with totipotency and ability to form germ cells.

13 A Section Through a Teratocarcinoma

14 MRI image showing brain midsagittal section

15 Primordial Germ Cells (PGCs) Somatic cells Genital ridge Bi-potent Gonads Sex Determination Testis and Sperm Ovary and Oocyte

16 Sex determination in Mammals SF1 IF XY SRY SOX9 Other genes} Testis WT1 LHX9 SF1 IF XX WNT4 DAX1 WT1 Wilton Tumor-suppressor 1, Transcription factor LHX9- Lim HomeoboX9, Transcription factor Other genes Ovary SF1- Steroidogenic Factor 1, Hormone receptor, transcription factor/activator

17 Sex determination in Mammals SF1 IF XY SRY SOX9 Other genes} Testis WT1 LHX9 SF1 WNT4 DAX1 IF XX WNT4 Other genes WNT4 (wingless in fly) wnt signaling pathway. Ovary

18 Wnt (wingless) signaling pathway

19 WT1 LHX9 SF1 Sex determination in Mammals IF XY SRY IF XX SRY WNT4 SOX9 DAX1 SF1 Other genes Other genes} Testis Ovary SRY (Sex-determination Region on Y chromosome) is a transcription factor

20 WT1 LHX9 SF1 Sex determination in Mammals IF XY IF XX SRY WNT4 SOX9 DAX1 SF1 Other genes Other genes} Testis Ovary DAX1 nuclear hormone receptor, transcription factor/inhibitor SOX9 (SRY-box9)- transcription factor/regulator

21 Sex determination in Mammals IF XY SRY SOX9 SF1 Other genes} Testis WT1 LHX9 SF1 IF XX WNT4 DAX1 Other genes Ovary

22 Sex determination in Mammals IF XY SRY SOX9 SF1 Other genes} Testis WT1 LHX9 SF1 IF XX WNT4 DAX1 Other genes Ovary

23 Sex determination in Mammals AMH: Anti Mullerian Hormone

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27 Gametes maturation

28 SF-Seminiferous tubules RT- Rete Testis E- Epididimis SF

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30 Sertoli cells secret GDNF Glial-Derived Neurotropic Factor

31 L- Leydig cells R- Rete testis V- Vasculture ST- Seminiferous tubule ST

32 The Formation of Syncytial Clones of Human Male Germ Cells

33 The Modification of a Germ Cell to Form a Mammalian Sperm

34 The Modification of a Germ Cell to Form a Mammalian Sperm

35 Structure of Sperm Actin centriole Flagella movement.wmv

36 Cytoplasm Yolk Oocyte Structure

37 The Ovarian Follicle of Mammals

38 The Ovarian Follicle of Mammals

39 Changes in the Number of Germ Cells in the Human Ovary over the Life Span

40 The Human Menstrual Cycle

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43 Meiosis in the Mouse Oocyte

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45 Fertilization

46 Fertilization Major questions: How do the sperm and egg find each other? How is species specific fertilization assured? How does the sperm penetrate the egg? How is single sperm entry achieved?

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49 External Fertilization Common to many invertebrates (model organism: sea-urchin) and vertebrates like fish and frogs Fertilization is in water outside the animal body where gametes from many species mix Gamete recognition is critical and relies on: Large numbers of gametes released both eggs and sperm Species-specific chemotaxis between sperm and eggs to ensure encounter Further Mechanisms ensuring species specific contact and penetration only - IVF in vitro fertilization

50 Internal fertilization Common to vertebrates like reptiles, birds and mammals, but also to invertebrates such as insects The sperm is deposited in the female tract but still has to find the eggs Much more sperm than eggs is released and the sperm has to be capacitated in order to be active in fertilization There may be chemotaxis towards the egg and recognition is still important, even though risk of competition with foreign gametes is low

51 Structure of an Egg at Fertilization

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54 The Egg Cell Surface

55 Acrosome Reaction

56 Acrosome Reaction

57 Acrosome Reaction

58 Acrosome Reaction

59 Fertilization Egg plasma membrane

60 Steps towards Fusion Contact between the sperm and the egg jelly initiates the acrosome reaction The enzymes released from the acrosome allow the acrosomal process to penetrate the egg jelly and reach the vitelline envelope ZP proteins on the acrosomal process binds its receptors in the vitelline envelope and a fertilization cone forms contact between the egg and sperm plasma membranes Membrane fusion is induced and the sperm pronucleus and centriole enter the egg

61 After Fusion Events Calcium wave, cortical reaction and formation of the fertilization membrane This happens about a minute after fertilization and it removes all surrounding sperm from the egg Sperm entry site Sperm entry site

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63 The Cortical Granule Reaction

64 Stages of the Cortical Reaction Sperm-egg fusion triggers release of calcium from ER and a calcium wave Cortical granules undergo exocytosis and fuse with plasma membrane The granules secrete: Proteases that cut connections to the vitelline envelope Proteases that cleave bindin receptors Polysaccharides which draw water into the space between the plasma membrane and the vitelline envelope

65 Cortical Reaction Stages (cont.) Peroxidases that cross-link tyrosine residues in the vitelline envelope and make it hard and impermeable to sperm The glycoprotein hyalin, which forms a layer next to the plasma membrane As a result the vitelline envelope is separated from the membrane and forms the fertilization envelope enclosing a thick hyalin layer. Both of which will protect the future early embryo

66 The Cortical Granule Reaction

67 The Cortical Granule Reaction

68 Sperm entry site Sperm entry site

69 The Cortical Granule Reaction

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72 In Vitro Fertilization

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