1. FERTILIZATION
Gametes: fuse to create a new organism
sex: combining the genes of both parents
reproduction: creation of a new organism
Steps
.Contact and recognition between gametes
. Regulation of sperm entry
. Fusion of genetic material
. Activation of egg

2. 7.2 The modification of a germ cell to form a mammalian sperm

3. 7.2 The modification of a germ cell to form a mammalian sperm (Part 3)

4. 7.3 The motile apparatus of the sperm
Axoneme

5. 7.4 Structure of the sea urchin egg at fertilization

6. 7.5 Stages of egg maturation at the time of sperm entry in different animal species

7. 7.6 The sea urchin egg cell surface
Enclosing the cytoplasm is the egg cell membrane which must be capable of fusing with the sperm cell membrane and must regulate the flow of certain ions during fertilization.
Outside of the cell membrane, there is a fibrous mat involved in sperm-egg recognition. In nvertebrates: vitelline envelope.
devbio8e-fig jpg

8. 7.7 Hamster eggs immediately before fertilization
In mammals, the vitelline envelope is a separate and thick extracellular matrix called zona pelucida.
The mammalian egg is also surrounded by a layer of cells called the cumulus.
The inner most layer of cumulus cells is called corona radiata.
Beneath cell membrane is the cortex (globular actin molecules and cortical granules).

9. 7.8 Summary of events leading to fusion of egg & sperm plasma membranes in the mouse

10. 7.9 Sperm chemotaxis in the sea urchin Arbacia punctulata (Part 1)
Resact is a 14 aa peptide that diffuses readily in seawater.
1 sec sec sec sec

11. 7.10 Model for chemotactic peptides in sea urchin sperm
devbio8e-fig jpg

12. 7.11 The acrosome reaction in sea urchin sperm
The acrosome reaction has 2 components:
1) the fusion of the acrosomal vesicle with the sperm cell membrane: the contact causes the exocytosis of the sperm’s acrosomal vesicle and the release of proteolytic enzymes.
2) the extension of the acrosomal process: the actin molecules assemble to produce microfilaments extending the acrosomal process onwards.

13. 7.12 Species-specific binding of acrosomal process to egg surface in sea urchins

14. 7.13 and 7.14 Localization of bindin on the acrosomal process and Bindin receptors on the egg

15. 7.15 Scanning electron micrographs of the entry of sperm into sea urchin eggs

16. Egg cell membrane increase the Na permeability.
7.17 Membrane potential of sea urchin eggs before and after fertilization
Fast block to polyspermy- change in the resting potential of the egg cell membrane.
Egg cell membrane increase the Na permeability.
Sperm cannot fuse with membranes having a positive resting potential.

17. Slow block of polyspermy- the cortical granules remove sperm
7.18 Formation of the fertilization envelope and removal of excess sperm
Slow block of polyspermy- the cortical granules remove sperm
Cortical granule serine protease: dissolves the protein posts that connect the vitelline envelope proteins to the cell membrane, and if clips off the bindin receptors and any sperm attached to them.
Fertilization envelope is formed (components of the cortical granules + vitelline envelope).
Mucopolysaccharides: elevate the fertilization envelope.
Peroxidase enzyme: hardens the fertilization envelope
Hyalin: forms a coating around the egg providing support during cleavage

18. 7.19 Cortical granule exocytosis (Part 1)

19. 7.19 Cortical granule exocytosis (Part 2)

20. 7.20 Wave of Ca2+ release across a sea urchin egg during fertilization
Upon fertilization, the concentration of free Ca2+ in the egg cytoplasm increases greatly.
The release of calcium comes from within the egg itself.
The release of Ca2+ starts at one end of the cell and proceeds actively to the other end.
Calcium ions are directly responsible for propagating the cortical granule reaction.
The calcium ions are stored in the endoplasmatic reticulum .
devbio8e-fig jpg

21. 7.22 Postulated pathway of egg activation in the sea urchin (Part 1)

22. 7.22 Postulated pathway of egg activation in the sea urchin (Part 2)

23. 7.30 Sperm-zona binding
Sperm - SED1- ZP complex
Galt activates G-protein that open Ca channels and initiate the acrosome reaction.

24. 7.33 Entry of sperm into a golden hamster egg (Part 1)
Sperm fusing the egg.
Sperm head passing through the zona pelucida
Hamster sperm fusing parallel to the egg plasma membrane.

25. 7.33 Entry of sperm into a golden hamster egg (Part 2)

26. 7.34 Pronuclear movements during human fertilization
Microtubules- green
DNA- blue
White arrows: sperm tail