From, Institut Jacques Monod, Paris, France

will give a seminar entitled:

Cell Division Geometries and Early Embryo Development

Abstract :
Life for all animals starts with the fertilization of the egg, followed by the centration of the sperm nucleus and a 3D-choreography of reductive cell divisions called cleavage patterns. These invariant morphogenetic processes rely on the precise motion, positioning and orientation of large microtubule (MT) asters. Using a combination of mathematical models, in situ force measurement and quantitative imaging, we demonstrate that the geometry of eggs and blastomeres may influence these early morphogenetic events. Our data support that dynein-dependent MT pulling forces exerted in the cytoplasm that scale to MT length may function as a general design to convert cell shape into net aster force and resultant motion and positioning. This design allows to account for the centration of sperm nuclei at fertilization, competition between symmetric and asymmetric divisions, as well as the geometry of cleavage patterns in multiple invertebrate and vertebrate species. These data raise important questions on the material properties of the cytoplasm and their impact on aster, spindle and division positioning. Methods to finely control division position and orientation will also be presented, as means to directly address the role of division positioning size in the regulation of key events during embryonic development, such as nuclear / cytoplasm ratios, cell cycle length and fate specifications.