Septins regulate contractility of the actomyosin ring to enable adherens junction remodeling during cytokinesis of epithelial cells. Roland Le Borgne, Nabila Founounou, Nicolas Loyer. Institute of Genetics and Development of Rennes CNRS UMR 6290-Faculté de Médecine 2 av du Pr. Bernard 35000 Rennes FRANCE.

   During cytokinesis, a contractile ring containing actin, myosin II and septins generates a furrow that divides one cell into two. How cytokinesis of epithelial cells making adhesive contacts with their neighbors is achieved is unknown. We report that, in Drosophila, septins are required for planar cell division, yet dispensable for orthogonal cell cytokinesis. During planar division, apicobasal integrity is preserved and furrowing is asymmetric with the contractile-ring displaced towards the adherens junction belt in a septin-independent manner. Local disengagement of adherens junctions between interphasic and mitotic cells is required to generate an adhesive interface between daughter cells. Loss of septins causes a two-fold reduction in the contractility of the actomyosin ring and prevents junction remodelling. Photo-ablation experiments reveal that septin-driven actomyosin contraction is needed to unzip E-cad contacts locally thereby allowing junction remodeling. Thus, septins exert a mechanical function needed to overcome the tension induced by adhesive contacts during cytokinesis.