Lecture 17: Fertilization Mechanism Flashcards
What are the steps of fertilization?
- Cumulus cell penetration using PH20
- Contact of sperm head with zona pellucida (ZP3 + ZP3 receptor on sperm)
- increases calcium level in sperm cytoplasm
- Acrosomal reaction to dissolve ZP
- Growth of acoromal process and fusion of plasma membranes
- Insertion of the sperm nucleus into the egg cytoplasm
What does GV stand for?
Germinal vesicle
Why do you want to stick in the ICSI needle for IVF?
AWAY from the polar body because it is usually close to the metaphase II spindle
What is the perivitelline space?
The space that is between zona pellucida and the zygote
This is where the 1st polar body is located
What is involved in sperm capacitation?
Takes place in endocervix, uterus, fallopian tube
SPERM MOTILITY MUCH IMPROVED
1. Loss of cholesterol from sperm plasma membrane
2. Changes in surface charge of proteins
3. Changes in phosphorylation of sperm proteins
4. Elevation of intracellular pH and bicarbonate
5. Changes in ion conductance
6. cAMP production results in development of hyperactivated motility
-characteristic of capacitated sperm
How does the sperm penetrate the cumulus cells?
- With the help of PH20, a cell surface hyaluronidase
Capacitated sperm penetrates the cumulus oophorus - Assisted by sperm motility
- may be group effort (sperm providing enzyme activity to help each other dissolve the hyaluronic acid matrix
How is the acrosome reaction triggered?
Complex-mediated signaling event that results in CALCIUM release within the sperm
Fusion Of sperm plasma membrane with outer acrosomal membrane
Release of acrosomal contents that includes enzymes that digest ZP
Where is the sperm capacitated?
In the female reproductive tract
Endocervix, uterus, fallopian tube
What does penetration of the zona pellucida require?
- requires motile force generated by flagellar movement
- requires ENZYMATIC HYRDOLYSIS by acrosomal proteases linked to the inner acrosomal matrix
- Angiotensin converting enzyme (ACE) releases GPI-linked proteins from the sperm surface and inner acrosomal matrix
- TESP5 (testis serine protease 5)
- PH-20 hyaluronidase
How is calcium release triggered?
By PLC activity
What is the significance of calcium oscillations in fertilization?
Initiates acrosomal reaction!!
Release of corticogranules so that no other sperm can fertilize?
1. Early event in fertilization is increase in sperm cytosolic calcium
2. Hallmark of initiation of egg activation
3. Calcium release triggered by PLC
4. Intracellular calcium chelators can block CG (corticogranules) release and resumption of meiosis
Makes it so that no other sperm can
What are the steps of egg activation?
Occurs after fertilization and involves completion of M2 and initiation of embryonic development
- release of meiotic arrest
- changes in maternal mRNA, proteins yntheis
- Exocytosis of cortical granules to block polyspermy
- cytoskeletal rearrangement
What is the significance of release of cortical granules from egg?
It blocks polyspermy
At level of membrane and zona pellucida
What are the characteristics of oocyte activation that is not sperm dependent?
- Mechanical trauma
- temperature shock
- chemical stimuli
- electrical signals
- Treatment with calcium ionophore (SrCl2)
- ICSI procedure
Parthenogenesis
What is parthenogenesis?
Asexual reproduction in which growth and development of embryos occur without fertilization
