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Equipes de recherche - Biologie du Développement de Villefranche sur mer
Unité Mixte de Recherche CNRS 7009





Egalement dans la rubrique



Images of organism : "Phallusia mammilata". Click image


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Meiotic cell cycle

In ascidians the unfertilized egg is arrested in meiotic metaphase I and passes into anaphase about 10 minutes after fertilization or egg activation.  A series of steps accompanies the unequal cleavages that produce polar bodies.  First the meiotic spindle migrates in an actin-dependent manner close to the cortex defining the animal pole of the egg and causes the overlying cortex to differentiate.  Second, following egg activation the cortex/plasma membrane overlying the meiotic spindle protrudes and one pole of the spindle rotates into the protrusion.  Finally, following Anaphase I the small protrusion cleaves from the egg discarding half of the chromosomes. Errors in this meiotic process cause trisomies in humans such as Down's syndrome.  We are using the egg of Phallusia mammillata to dissect the molecular pathway by which fertilization and calcium elevation induce meiotic spindle rotation, metaphase-anaphase transition, and proper chromosome segregation.