1. Oogenesis Behind every successful embryo stands a hard-working mother.

2. Eggs are enormous cells carrying nutrients for the developing embryo Why? Mass of egg must equal the mass of the embryo that emerges!

3. Even human eggs are huge cells

4. Eggs are enormous cells carrying nutrients for the developing embryo yolk=large stores of nutrients large stores of macromolecules most eggs surrounded by a coat or shell

5. The germ line is set aside early in development as a separate cell lineage This can sometimes be visualized by the segregation of putative "determinants” as in C. elegans Fertilized egg "P granule" mother cell of germline = P4 P1 HOW are P-granules segregated? PAR proteins & microfilaments see p. 246 and Fig. 8.43

6. C. elegans: P granules are segregated at each division and make the cell that inherits them the germline Figure 8.44 cell nuclei P-granules

7. Similar mechanisms lead to very early segregation of the germline in the fruit fly Drosophila Germ cell progenitors A P

8. The Germline is also set aside in Humans Oocytes arrest in prophase of meiosis I for up to 50 years! Figure 19.23

9. How does a single egg cell make all the stuff needed to start development?

10. Fly Oogenesis

11. Nurse cells are mitotic sisters of the oocyte Figure 19.4

12. Nurse cells synthesize macromolecules and pump them into the oocyte through the cytoplasmic bridges nurse cells follicle cells

13. The Drosophila ovary is composed of somatic follicle cells, germ line nurse cells, and the oocyte

14. Most of the instructions for forming organisms are already in the egg! Asymmetric distribution of egg contents influences embryonic development

16. Molecules synthesized by the nurse cells and specifically localized in the oocyte determine the anterior/posterior axis of the embryo Posterior Determinant (nanos) Anterior Determinant (bicoid) Oocyte Specific mRNAs are bound by proteins and transported along microtubules by motor proteins to their destinations

17. Ventral follicle cells build a signal into the egg shell that determines the dorsal/ventral axis of the embryo Ventral follicle cells Oocyte signals follicle cells, follicle cells signal back to oocyte cytoplasm nucleus gurken mRNA PosteriorAnterior Dorsal Ventral Torpedo receptor binds Gurken; signal inhibits Pipe in dorsal follicle cells Pipe protein See Fig. 9.11 for more details

18. Pipe intiates a signaling pathway for activation of Dorsal transcription factor in ventral cells only Ventral signal initiated by Transmembrane receptor (Toll) Signaling pathway Transcription factor (Dorsal) relocalized to ventral nuclei of embryo activating new genes Pipe

19. Localized mRNAs also influence vertebrate development Vg1 mRNA See also Figure 5.38

20. Human oogenesis: An example of hormonal control of reproduction Meiosis I 2 million present at birth ovulation

21. Cyclic changes in hormonal signals regulate the timing of female reproduction Most mammals- once/year Humans- monthly Release into the Fallopian tube (Turns off FSH and LH!)

22. Cyclic changes in hormonal signals regulate the timing of female reproduction (Turns off FSH and LH!) Release into the Fallopian tube RU486- blocks progesterone receptors Plan B-progestin (interferes with ovulation, fertilization, implantation) Progesterone and estrogen birth control pills- prevent maturation of new ova

23. Anton van Leeuwenhoek WNYC’s Radiolab clip from “Sperm” (12/2/08) By Jad Abumrad & Robert Krulwich

24. Figure 7.1 The Human Infant Preformed in the Sperm, as Depicted by Nicolas Hartsoeker (1694)

25. The sperm: a stripped down machine for delivering DNA Figure 7.2

26. Chemical cues from the egg attract sperm In sea urchins, the cue is resact Inject resact Figure 7.9 Sperm chemotaxis 0 sec 20 sec 40 sec 90 sec

27. Step one: Contact between the sperm and the eggshell

28. Step two: Contact between the sperm and the egg’s plasma membrane

29. Fertilization: a multistep process (zona pellucida=egg shell)

30. Sperm-eggshell contact triggers the acrosome reaction Example 1-- the sea urchin enzymes Species specificity (equivalent to zona pellucida)

31. attracts/activates sperm Figure 7.8

32. Sperm-eggshell contact triggers the acrosome reaction Example 2: Mammals Eggshell includes ZP3/Sperm have ZP3 receptor

33. Figure 7.8

34. BLOCKING POLYSPERMY 1.Fast/transient: prevent sperm fusion 2.Slow/permanent: removal of other bound sperm

35. Fast block 1-3 seconds lasts 1 min Slow block 20-60 seconds permanent

36. How do we know this? We can measure these events directly! Figure 7.17Membrane potential of sea urchin eggs before and After fertilization. resting -70 (sperm can fuse with egg) (sperm can’t fuse with egg) +20 mV

37. Cortical granules: poised for release 15,000 cortical granules in a sea urchin egg contain enzymes that clip the egg’s bindin receptor and any attached sperm alter the vitelline envelope (zona pellucida in mammals so that ZP3 receptor on sperm cannot bind) Blocking polyspermy: SLOW BLOCK Figure 7.6

38. Sperm-eggshell contact triggers the acrosome reaction Example 2: Mammals Sperm have ZP3 receptor

39. A wave of increased calcium can be visualized moving across the egg from the point of sperm entry Figure 7.20

40. Fast block 1-3 seconds lasts 1 min Slow block 20-60 seconds permanent