At high or low trp concentration, RNA Polymerase synthesizes full mRNA till region 4

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#Id: 7609

#Unit 5. Developmental Biology

Slow Block to polyspermy

When the cortical granules fuse with the egg cell membrane, they release protein-digesting enzymes that modify the zona pellucida proteins such that they can no longer bind sperm

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#Id: 7610

#Unit 5. Developmental Biology

Cortical granule proteases is ovastacin When ZP2 is cleaved by ovastacin, it loses its ability to bind sperm

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#Id: 7611

#Unit 5. Developmental Biology

Polyspermy occurs more frequently in mouse eggs bearing mutant ZP2 that cannot be cleaved by ovastacin

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#Id: 7612

#Unit 5. Developmental Biology

A second slow block to polyspermy comes from the so-called zinc spark, the release of billions of zinc ions that is induced by the entry of the first sperm These released zinc ions are bind to the zona pellucida

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#Id: 7613

#Unit 5. Developmental Biology

Acrosomal enzymes (acrosin and MMP2) as well as the enzymes that help establish capacitation, are inhibited by zinc, the accumulation of zinc on the zona pellucida and in the surrounding cumulus form a “zinc shield” that prevents further sperm entry

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#Id: 7614

#Unit 5. Developmental Biology

Mechanisms of Egg Activation