Syndapin functions in orchestrated remodelling of the membrane and actin cytoskeleton

Abstract

The syncytial nuclear division cycles during early Drosophila embryo development involvesorchestrated remodelling of the membrane and cytoskeleton We have shown that the F BARdomain protein Syndapin that is known to have roles in membrane tubulation endocytosisand cytoskeletal remodelling is increasingly enriched at the tip of syncytial pseudocleavagefurrows with each nuclear cycle The dynamics of pseudocleavage furrow progressiondepends on Syndapin function We showed that Syndapin function was important forrecruitment of septin Peanut and organization of the formin Diaphanous at the furrow tipdownstream of the furrow initiation protein RhoGEF2 Syndapin depleted embryos showeddisorganized actin on the furrow also seen in RhoGEF2 mutants Interstingly Syndapinoverexpression in RhoGEF2 depleted background restored actin organization and extent offurrow ingression Addtionally we showed that Syndapin or RhoGEF2 depletion causesreduction in the number of Rab5 puncta however Syndapin overexpression in RhoGEF2 depleted background cannot restore the number of Rab5 puncta Therefore we conclude thatSyndapin can rescue the furrow extension phenotype by actin organization alone and notbecause of its role in early endocytosis Actin turnover is also crucial for dynamic expansion of the apical caps prior to furrowformation Arp2 3 function is important for expansion of the apical cap We find thatsyndapin mutants limit cap expansion and show abnormally large actin caps We are able torescue this cap expansion phenotype by combining mutants of a component of the Arp2 3complex ArpC1 with the syndapin mutant Using TIRF microscopy we find thatremodelling of apical actin structures is defective in these mutants giving rise to the observedphenotypes Therefore Syndapin and Arp2 3 complex oppose each other to regulatedynamics of actin cap expansion in the syncytial embryo Apical c newline newline