Septin complexes: Ahead of the curve.

Individual cells have robust repair systems to survive cell cortex damage caused by mechanical and chemical stresses, allowing them to maintain the integrity of tissues and organs. The contraction of an actomyosin ring at the wound edge is a major mechanism for physically closing the cell wound. In contrast to polymerization and bundling of actin filaments, little is known about how linear actin filaments are bent to be integrated into the actin ring structure encircling the wound edge. We recently found that the five Drosophila Septins function simultaneously in the regulation of actomyosin ring assembly, contraction, and disassembly during cell wound repair. These Septins form two distinct complexes-Sep1-Sep2-Pnut and Sep4-Sep5-Pnut-composed of different subunits from the same groups. Strikingly, these two distinct Septin complexes have different degrees of F-actin bending activities that are consistent with their spatial recruitment: different degrees of curved actin filaments are required for the robust formation of different regions of the actomyosin ring. In addition, we found that the two Septin complexes are regulated by different molecular pathways as a loss of Anillin only affects Sep1-Sep2-Pnut complex recruitment. These findings open new directions for how individual Septin subunits form complexes and function differentially in cellular and developmental processes.