From: Laboratoire de Biologie du Développement de Villefranche-sur-mer (LBDV), France

Will give a seminar entitled:

Emergence of embryonic shape

Although different classes of embryos display predictable patterns of early cleavage divisions up to the blastula stage, we still do not understand what generic rules lead to one or another embryonic shapes. Difficulty in answering this question is due to the lack of mechanistic understanding of how cell shape, cell tension, cell adhesion and cleavage patterning and timing are coordinated. Even though significant progress has been made in identifying the genes involved in driving cell fate decisions, this reductionist one gene-one function approach has led to comparatively less progress in understanding how cleavage patterns and overall embryonic shape emerges.

We exploit the invariant cleavage pattern displayed by ascidian embryos to tease apart the cell biological and biomechanical forces involved in underpinning the invariant cleavage pattern. Invariant cell positioning in the compact ascidian embryo is important for cell-cell signaling starting at the 32-cell stage when 4 animal blastomeres are induced by vegetal blastomere derived FGF to become neural precursors. We have so far found a number of mechanisms that work together to create the invariant cleavage pattern and maintain a compact embryo (that does not have a blastocoel): cell cycle asynchrony, unequal cell division, long apical length dependent spindle positioning and mitotic apical relaxation. I will present what we have done and are doing and try to give an overview of how the ascidian invariant cleavage pattern emerges.

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