Fertilisation Flashcards
How do sperm gain their fertilising capacity? (2)
- Interactions with the female reproductive tract.
- Sperm Capacitation
Define Sperm Capacitation (4)
Further and final maturation process which confers the following functional
characteristics on to sperm and ultimately renders them capable of fertilisation:
- A change to a state of hyperactivated motility.
- The ability to bind to the oocyte’s zona pellucida and afterwards undergo the acrosome reaction.
- The capacity to fuse with the oocyte
Name the 4 female tract Interaction mechanisms (4)
Chemotaxis
Thermotaxis
Rheotaxis
Boundary-following navigation
Define Chemotaxis (3)
— Chemical guiding mechanism.
— Sperm responding to a gradient of chemoattractant e.g. steroid hormones.
— Molecular and behavioural mechanisms yet to be fully understood
Define Thermotaxis (3)
— Temperature guiding mechanism.
— Female tract consists of different areas with marginal differences in temperature.
— Sperm responding to changes in the extracellular temperature gradient.
Define Rheotaxis (3)
Ability to respond to fluid currents in the female tract environment.
Define Boundary-following navigation (4)
— Ability to turn corners in response to surface boundaries
— Human sperm with preference to follow boundaries on the left or right hand side have been shown to possess higher DNA integrity than straight swimming sperm
The Sperm Capacitation Puzzle
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Sperm-oocyte interaction - 4 steps (6)
- Once a few capacitated sperm make it to the site of fertilisation, they come
in contact with the cumulus-oocyte complex (COC) and a much higher
concentration of follicular fluid (FF). - FF in addition to secretions from the COC e.g. progesterone further modulate the spermatozoa to initiate the process of sperm-oocyte interaction and subsequent fertilisation:
— Penetration of the cumulus oophorus
— Sperm-zona binding
— Acrosome reaction
— Sperm-oocyte fusion and oocyte activation
Penetration of the cumulus-oophorus
Once sperm come in contact with the cumulus-oophorus cell mass surrounding the oocyte, the enzyme hyaluronidase present on the surface of the sperm head dissolves hyaluronic acid (hyaluronan) – the major
cementing factor between cells that constitute the cumulus oophorus cell mass.
Sperm-zona binding (3)
- Four zona pellucida (ZP) glycoproteins expressed – ZP1, ZP2, ZP3, ZP4.
- Studies across mammalian species have shown that sperm bind to ZP2 and ZP3 via receptors present on the sperm’s plasma membrane.
- Recent studies show that human sperm bind to ZP2.
Acrosome Reaction (3)
- Triggered in response to sperm-oocyte interaction
- Fusion of the sperm’s plasma membrane with it’s outer acrosomal membrane.
- Results in the release of hydrolytic and proteolytic enzymes e.g. hyaluronidase and acrosin.
Sperm-oocyte fusion & oocyte activation (4)
Intracellular calcium spike + Cortical reaction =
1)Release from meiotic arrest and completion of meiosis II.
2)Incorporation of sperm DNA and pronuclear formation.
3)Embryo cleavage
How does the sperm trigger oocyte activation? (4)
Phospholipase C Zeta (PLC ζ). (PLC ζ + PIP2 = IP3 + DAG)
* Discovered in 2002 by Saunders et al. and widely accepted as the oocyte activation factor introduced by sperm.
- Acts by activating inositol trisphosphate (IP3) production, leading to repetitive calcium release (oscillations) from the oocyte’s calcium stores.
- Has been identified in all species studied so far, including human
What 2 things do you look at for fertilisation? (2)
Pronuclei
Polar bodies
