François Robin (IPBS, UPMC, Paris). ENS-ESPCI Biophysics Seminar

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21 April 2017 13:00 » 14:00 — ESPCI, Amphi Urbain, Ground Floor, Staircase N

Organizing embryonic contractility in space and time.

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.
First I will discuss our recent work on neural tube closure in a basal Chordate, Ciona intestinalis. Using live imaging and laser microsurgery, we 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.
I will then turn to a different model system, the 1-cell stage C. elegans embryo and present our recent findings on contractility dynamics in this system that sheds light on the molecular bases of actomyosin contractility. We 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, we 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.
Finally, 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.

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