Fertilisation

Question 1

In sea urchins, chemotaxis of sperm to egg occurs in response to what molecule?

Answer 1

14 amino acid RESACT peptide

Question 2

Carbohydrate signals from the sea Urchin egg trigger what response in the sperm?

Answer 2

Ca2+ mediated exocytosis of acrosomal vesicle

Question 3

What actin-dependent process occurs after enzymes are released from the acrosome?

Answer 3

Formation of the acrosomal process

Question 4

Species recognition occurs through…

Answer 4

Binding of species specific protein to acrosomal process

Question 5

In mammals, which two proteins facilitate the binding of the acrosome to the surface of the egg?

Answer 5

IZUMO (acrosome) and JUNO (egg)

Question 6

How is polyspermy rapidly blocked after fertilisation?

Answer 6

Membrane depolarization

Question 7

How is the Ca2+ wave initiated?

Answer 7

1. Phosphatidyl inositol (PI) is phosphorylated twice to form Phosphatidyl inositol (PIP2)
2. When activated, Phospholipase C (PLC) breaks down PIP2 into diacylglycerol (DAG) and Inositol trisphosphate (IP3)
3. DAG recruits Protein kinase C
4. IP3 binds to IP3 receptor on Endoplasmic reticulum, causing it to release Ca2+ into the cytoplasm
5. PKC is activated by calcium, causing it to phosphorylate targets across the plasma membrane
6. Other IP3 receptors on the ER are activated by Ca2+, leading to a wave of Ca2+ release.
7. Once completed, physical contact between STIM1 (ER) and ORA1 (PM) opens Ca2+ channel in PM, Ca2+ is then pumped into ER by SERCA

Question 8

What are the two models for PLC activation?

Answer 8

1. Egg-receptor mediated- sperm derived factor (fertilin) activates egg receptor (integrin)
2. Sperm oocyte-activating factor (SOAF)

Question 9

What potential mechanisms could the SOAF model involve?

Answer 9

1. Sperm directly releases IP3
2. Sperm activates src-tyrosine kinases, which activate PLC
3. Sperm introduces its own PLC(zeta) isoform.

Question 10

What other pathway involves Calcium-induced calcium-release?

Answer 10

Ryanodine pathway (ryanodine is a toxin, which impacts the release of calcium into the muscles.)

Question 11

Why do IP3 receptors behave as if they are spatially separated, despite being on a contiguous compartment (ER)?

Answer 11

High number of calcium buffering proteins in the ER. (Further explained in yr2)

Question 12

How does Ca2+ wave activate the slow block to polyspermy

Answer 12

Stimulates fusion of cortical granules with plasma membrane, forming a fertilization envelope.

Question 13

What is the fertilization envelope made up of?

Answer 13

Mucopolysaccharides, cross-linked vitelline proteins and hyalin.