Fertilization Mechansims Flashcards
What are the 6 steps of fertilization?
- Contact
- Acrosomal rxn
- Growth of acrosomal process
- Fusion of plasma membranes
- Entry of sperm nucleus
- Cortical reaction
What does the maturation of the oocyte involve?
- Resumption of meiosis within the follicle (LH surge)
- Expansion of granulosa cells (cumulus oophorus)
- Extrusion of first polar body
- Formation of M2 spindle
- Ovulation of M2 arrested egg
Where is the 1st polar body?
Close prox to M2 spindle
What is sperm capacitation?
Sperm develops “capacity” to fertilize an egg. Normally within the female reproductive tract through which the sperm’s motility increases.
What changes in sperm occur during capacitation?
- Loss of cholesterol from plasma mem
- Changes in surface charge of proteins
- Changes in phos of sperm proteins
- Elevation of intracellular pH and bicarbonate
- Changes in ion conductance
- cAMP production results in dev of hyperactivated motility *
How does the sperm penetrate the culumus cells?
“Group effort”: many sperm provide enzyme PH20 and TESP5 activity to help each other dissolve the hyaluronic acid matrix. The process is assisted by sperm motility
How is the ZP penetrated?
Acrosome reaction triggered and there are ZP3 protein interactions resulting in ca2+ release within the sperm. Sperm then releases content of acrosome to help digest ZP. Penetration requires motile force generated by flagellum and enzymatic hydrolysis.
What is the next step after ZP is penetrated and describe it
Sperm and egg plasma membrane must fuse. Occurs on an equatorial plane and takes about 3 hrs in vitro.
Describe the changes in Ca2+ once sperm enters egg
Distinct events of egg activation are initiated and completed by different number of Ca rises. Early on, there is in an inc in cytosolic Ca triggered by PLC activity.
When does egg activation occur and what does it involve?
After fert and involves completion of 2nd meiotic division and initiates embryonic dev
What blocks polyspermy?
Exocytosis of cortical granules, membrane and ZP block
What is parthenogenic activation?
Activation of egg without entry of sperm nucleus. Can occur as a result of trauma, temp shock, treatment with Ca or ICSI
Describe intrautarine insemination
- Remove seminal fluid
- Medium with protein and buffers to promote capacitation
- Swim up techniques to choose motile sperm (ie most motile move up to top of solution)
Describe ICSI
Injection of single sperm into oocyte
What is a globozoospermia?
Rounded headed sperm that lack an acrosome
