Embryogenesis Flashcards
(94 cards)
What do oviduct epithelial cells do?
Bind sperm
Make them briefly immobile
Stabilise sperm after capacitation
When do sperm reacquire mobility?
Ovulation
How is oocyte moved to the ampulla?
Swept along by cilia and muscle contractions
Where does fertilisation take place?
The ampulla
What three events does fertilisation require?
- Activation of sperm
- Establishment of diploidy
- Activation of ovum
What induces sperm activation?
- Progesterone from cumulus cells
2. Binding to zona proteins on oocyte
What does sperm activation cause?
- Hyperactive tail movement - whiplash
2. Acrosome reaction
What promotes hyperactive sperm tail movement?
Opening of calcium channels to activate PKC
What is the acrosome reaction?
- Fusion of outer acrosome and sperm plasma membranes
- Phospholipase C and SNARE proteins involved
- Release of hyaluronidase and exposure of acrosin on inner acrosome membrane
What are the zona pellucida proteins?
Glycoproteins
ZP1-4
What do ZP1, ZP3 and ZP4 do?
- Bind capacitated sperm
2. Induce acrosome reaction
What pathway does ZP3 activate?
Gi protein-coupled receptors on sperm
What does ZP2 do?
Weakly binds capacitated sperm to allow progression through zona
What allows sperm to burrow through zona pellucida?
- Acrosin - protease
2. Physical movement
What space does sperm enter once it penetrates zona?
Perivitelline space
Where does membrane fusion occur in the mouse?
Equatorial region away from female pronucleus
Enveloped by microvilli
What does the microvillus-free area of the oocyte signify?
Position of female pronucleus
What are the three proteins essential for binding?
- Izumo1 (sperm)
- Juno
- CD9
What is Izumo1?
Ligand on sperm essential for binding
What is Juno?
Izumo1 receptor on oocyte
What is CD9?
Tetraspanin on oocyte
Binding partner for Juno
What is syngamy?
Combining of chromosomes
How is the oocyte activated?
- Wave of calcium release across oocyte from site of sperm fusion
- Initiated by PLCζ enzyme from sperm
- Helps to prevent polyspermy
What is the cortical reaction?
Release of cortical granules stimulated by calcium waves
Fill perivitelline space
Ovastatin cleaves binding sites on ZP3/4 and ZP2 so that sperm can no longer bind
Zona proteins become cross-linked
Juno receptor exocytosed