Internal fertilization in Mammals

Set of Capacitation events

1. The sperm cell membrane is altered by the removal of cholesterol by albumin proteins. This moves lipid rafts with specific receptors on them 2. Particular proteins or carbs on the sperm surface are lost. It is possible that these compounds block the recognition sites 3. The membrane potential of the sperm cell membrane becomes more negative as potassium ions - allow ca2+ channels to be opened 4. Protein phosphorylation occurs 5. The outer acrosomal membrane changes and comes into contact with the sperm cell membrane

Penetrating the ZP

Analogous to the VE, but thicker and denser structure. Made of three major glycoproteins: zp1, zp2, zp3 (zp4) This binding of sperm to the zone is relatively species-specific Need to have undergone the acrosomal rxn in order to bind

Connection between translocation and capacitation

Before entering ampulla, uncapacitated sperm bind actively to the membrane of the oviduct cells which lengthens the sperms life span as well as slow down is Capacitation. This may fxn as a block to polyspermy by preventing many sperm from the reaching the egg at the same time. Max the prob that sperm will still availability to meet the egg in the ampulla

What happens to the sperm in the vicinity of the oocyte?

Hyperactivation: may enable sperm to sense a chemotactic gradient. Enables the sperm to digest through the cumulus cells Thermotaxis: Heat is one cue that capacitated sperm can use to find the eggs. Only in capacitated sperm Chemotaxis: once in the ampullary region, attract capacitated sperm to the egg.

Translocation

Of sperm from vagina to the oviduct Appears to be transported by the muscular activity of the uterus. The region of the oviduct fight before the ampulla may slow down sperm and release them slowly Sperm mobility is important once sperm arrive within the oviduct, sperm become hyperactive in the vicinity of the locate Directional cues from temperature cues Sperm matures through trek from vagina to ampulla

Progesterone

Secreted from the cumulus cells and used for direction. Receptors that activates the ca2+ channels and leading to sperm hyperactivity.

Gamete fusion

Side of sperm head makes contact Equatorial region: junction between inner acrosomal membrane and sperm cell membrane. Site where membrane fusion begins Immunoglobulin like protein izumo may be important for fusion.

Polyspermy preventiom

Slow block in the form of CG rxn. : enzymes released modify the ZP sperm receptor proteins such that they can no longer bind sperm.

Fusion of genetic material

The dna of the sperm pronucleus is bound by protamines- basic proteins that are tightly compacted through disulfide bonds. Protein in the egg cytoplasm reduces these bonds and allows sperm chromatin to uncoil. Calcium oscillations brought about by sperm entry inactivate MAPK and allow dna synthesis. This oscillation also activates another kinase that leads to the proteolysis of cycling and securin which eventually results in a haploid female pronucleus. Dna synthesis occurs separately in the male and female pronuclei Microtubules join the pronuclei and enable them to migrate towards each other.

Ampulla

The region of the oviduct where feetilization takes place

Capacitation

The set of physiological changes by which sperm become competent to fertilize the egg (Unable to undergo acrosomal reaction or fertilize until they have been in the female reproductive tract for some time)

Mammalian egg activation

Transient rise of cytoplasmic ca2+ is necessary, it is induced by the sperm Through ip3 pathway Regulation of oscillations time activatiom