Molecular Mechanisms of Fertilisation Flashcards
What happens what capacitation was carried out in vitro in the presence of albumin?
Albumin absorbs small molecules, including the cholesterol in sperm membranes. This made the membranes more fluid which increased the phosphorylation of protein kinases, leading to the activation of AR and hyperactivated motility.
What are the main glycoproteins in the ZP and what are their functions?
ZP1 - structural protein which cross-links other components.
ZP2 - receptor function and structural integrity.
ZP3 - receptor function and structural integrity; also involved in first primary binding and is the main agonist in the acrosome reaction (AR).
What initiates the AR?
Contact with ZP3 molecules on the zone. Purified or recombinant human ZP3 in soluble form will also cause induction.
What is the zona receptor kinase (ZEK)?
It a complementary receptor to ZP3 on the sperm membrane overlying the acrosome. It is a 95kD phosphotyrosine type receptor and of sperm-egg contact it aggregates, resulting in autophosphorylation and a kinase cascade, which leads to calcium influx and hence the AR.
What is thought to impart species specificity in gametes?
The sugar determinants of sperm and egg receptors.
What has been proposed in the mediation of the later stages of AR?
Phosphoinositide pathways involving PLC have been proposed. PLC contains src homology 2 (SH2) domains which interact with activated ZK2. Mouse sperm has shown zona proteins activate PLC, modulated by tyrosine phosphorylation.
How is secondary sperm-egg binding initiated?
The inner acrosomal membrane adhering to ZP2. This is mediated through acrosin and inhibition with protein C inhibitor prevents most sperm-zona binding in vitro.
What does the force of the sperm do to the zona?
It changes the zona matrix from its natural jelly composition to a fluid.
What receptors are important for gamete fusion?
Probably integrins such as those with RGD domains. A main sperm receptor is IZUMO and as well as others, shows similarity to viral fusion proteins. Also a tetraspanin molecule, CD9, on the egg is important for fusion.
Upon fusion, what causes a loss of sperm motility?
Ionic changes in the flagellum.
What is the main mechanism proposed for the resumption of meiosis in the egg?
Oscillin, from the sperm equatorial region, has been identified as a sperm-specific form of PLC. It diffuses into the egg cytoplasm and causes the release of stored calcium in the ER, resulting in calcium oscillations.
What is the mechanism in the prevention of further sperm entry upon fertilisation?
Cortical granules are released from the egg peripheral cytoplasm, which contain proteases which modify ZP3 so that the sperm can no longer bind to it. In some species, the proteases may also affect the oolemma so that the sperm cannot fuse with it.
What is agreed about the molecular details of capacitation?
That it arises from multiple molecular changes in the plasma membrane, but the exact sequence of events is unclear and may be variable.
