BIOL303 Lecture Notes - Lecture 12: Zona Pellucida, Embryogenesis, Trophoblast
3 Oct 2017
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Early mammalian development: difficult to study because the eggs are very small and there are only a few number of eggs produced at any one time. One is meridonial and the other is equatorial. Mammalian cleavage: cleavage divisions are slow and asynchronous. This (cid:373)ea(cid:374)s that (cid:449)e do(cid:374)"t o(cid:271)ser(cid:448)e a stri(cid:272)t 2, 4, 8, etc geometric progression: the genome is activated at a very early stage in mammalian cleavage. The mid-blastula transition (mbt) where zygotic genes start being expressed occurs extremely early at the 2 cell stage. In most other organisms, 10-12 divisions happen before zygotic genome activation (mbt: zygotic genome activation is required for cleavage and early development. These events do not rely on maternal transcripts and proteins (unlike the organisms we have previously studied: the best-studied mammalian system is the mouse. Good genetics and genetic tools: compaction in mammalian cleavage is also different from other systems, following the third division, blastomeres express e-cadherin and the cells become tightly.
