Dr. François ROBIN

Laboratoire de Biologie du Développement,
UMR 7622, Institut de Biologie Paris-Seine

Jeudi 07 Janvier 2016 à 11h00, Ecole Polytechnique, Amphithéâtre Becquerel

Zipping and pulsing : actomyosin dynamics in morphogenesis, from tissue to single molecules

The mechanical properties of embryonic cells define the landscape that drives morphogenesis. These mechanical properties derive from the actomyosin cortex, a ~200nm-thick active gel. Combining classical embryology, live imaging and numerical simulations, we have been able to dissect cortical dynamics and build a picture of morphogenesis across scales, from tissues to cells to molecules.

During my postdoc, I first focused on neural tube closure in a basal Chordate, Ciona intestinalis. Using live imaging and laser microsurgery, I could show that local activation of the motor protein myosin causes a local increase in junctional tension. Using numerical simulations, we then demonstrated that dynamic imbalance in tissue resistance converts this local contractile tension into asymmetrical junction shortening, unidirectional zipper progression and closure of the neural tube.

To gain further insight on the molecular bases of actomyosin contractility, I then turned to a different model system, the 1-cell stage C. elegans embryo. I established a technique to image and track single-molecules at the cell surface, and extract kinetic and kinematic properties of cortical proteins. Using this technique, I could show that actomyosin contractility is not self-organized, but emerges instead from the local modulation of actin and myosin turnover by an upstream regulator, Rho-1.

I will argue that the next step that we need to take to understand morphogenesis is to bridge in vivo the gap between the biochemistry of the actomyosin system, and the emergent, robust mechanical properties of the cortex.