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Biologie du Développement de Villefranche-sur-Mer

Mitotic control of cleavage in animal embryos

   Despite the essential role of the spindle assembly checkpoint in somatic cells, work in frog, worm and fish embryos has shown that microtubule perturbations that lead to erroneous kinetochore-spindle associations do not block mitosis during early embryogenesis, suggesting that the SAC is relaxed in early metazoan embryos. A main interest of our group is to understand how the spindle checkpoint is maintained silent in embryos and to molecularly dissect mitotic control during development, to determine how the mitotic machinery has adapted to the embryonic cell cycle and how aneuploidy is prevented during embryonic development.

   The data currently available on spindle checkpoint response during development are difficult to compare, as they refer to different embryonic stages and different microtubule perturbations. To evaluate the variability in spindle checkpoint activity during different embryonic stages, we are currently performing a multispecies comparison of the mitotic response to microtubule depolymerization in embryos representative of the major metazoan groups : cnidarian (Clytia hemisphaerica and Nematostella vectensis), mollusks (Mytilus galloprovincialis), echinoderms (Paracentrotus lividus, Sphaerechinus granularis, Arbacia lixula and Strongilocentrotus purpuratus), cephalochordates (Branchiostoma lanceolatum) and tunicates (Phallusia mammillata and Ciona intestinalis).

   At the molecular level, the simplest explanation for the lack of SAC signalling would be the absence of one or more components involved in SAC signalling in early embryos. However, by analysing transcriptomic data available for Phallusia, Ciona and Branchiostoma eggs and early cleavage embryos and by performing RT-PCR on total RNA from Paracentrotus eggs and embryos, we found that all SAC components are present, at least as transcripts, in eggs of all these animals both before and after fertilization. We are currently analysing the spatio-temporal distribution of key SAC components in the presence and absence of spindle perturbations. Using a combination of biochemical and proteomic appraoches, we are also analysing the protein complexes associated with the main SAC components during unperturbed mitosis and in the presence of mitotic insults, to identify the factors that modulate spindle checkpoint activity in embryos.


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