BIOL 3010 Lecture Notes - Blastocoel, Tight Junction, Syncytiotrophoblast
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Published on 29 Jan 2013
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Outline of Lecture 03
Fertilization, Preimplantation Development, and Implantation
I. Fertilization
1) Penetration of corona radiata
- Corona radiata is hyaluronic rich ECM; sperm has hyaluronidase
- A Ca2+ channel, CatSper, is required in sperm for penetration
2) Binding to zona pellucida
- Zona pellucida is a coat of glycoproteins, 13 µm thick, made of ZP1,2,3
subunits
- ZP3 is the target of species specific receptor on sperm, perhaps
β-1,4-galactosyltransferase
3) Acrosome reaction and penetration of zona pellucida
- Acrosome reaction is fusion of acrosomal membrane with sperm plasma
membrane
- Sperm binding to ZP3 causes rise in [Ca2+]in; signaling also requires
PLCδ4
- Sperm remains bound to ZP2 during this time
- Acrosin plays a non-critical role in penetration, not fully understood
4) Fusion of sperm and egg membrane
- Mediated by egg integrin binding to sperm fertilin
5) Cortical reaction
- Oscillating waves of Ca2+ causes cortical granules to be released,
triggered by PLCζ
6) Block to polyspermy
- Hardening of zona pellucida by cortical enzymes that alter ZP2 and ZP3
- Pronuclei fuse and cleavage divisions begin
II. Preimplantation Development (single cell to blastocyst)
1) Cleavage divisions
- Division without change in total size of embryo
2) Compaction
- Outer blastomeres form tight junctions using E-cadherin, this gives
in/out polarity
3) Formation of trophectoderm and inner cell mass
- Oct4 is a txn factor for Fgf4, both expressed in ICM and required for
trophectoderm proliferation
4) Blastocyst expansion
- Fluid filled blastocoel cavity develops by pumping by trophectoderm
5) Hatching
- strypsin helps blastocyst hatch out of zona pellucida
- Embryonic gene activation occurs at very early stage in mammals
- Epigenetic imprinting also occurs
III. Implantation
- Implantation is needed so that embryo can get energy from the mother