Nanoscale Indentation of Plasma Membrane Establishes a Contractile Actomyosin Scaffold Through Selective Activation of the Amphiphysin-Rho1-Dia/DAAM and Rok Pathway

Abstract

Nanoscale bending of plasma membrane increases cell adhesion, induces cell-signalling, triggers F-actin assembly and endocytosis in tissue-cultured cells. The underlying mechanisms are not very well understood. Here, we show that stretching the plasma membrane of somatic cyst cell around rigid spermatid heads generates a stable, tubular endomembrane scaffold supported by contractile actomyosin. The structure resembles an actin-basket covering the bundle of spermatid heads. Genetic analysis suggests that the actomyosin organisation is nucleated exclusively by the Formins, Diaphanous and DAAM, downstream of Rho1, recruited by the Bin-Amphyphysin-Rvs (BAR)-domain protein, Amphiphysin, around the spermatid heads. Actomyosin activity at the actin-basket gathers the spermatid heads into a compact bundle and resists the invasion of the somatic cell by the intruding spermatids. These observations revealed a new response mechanism of nanoscale bending of the plasma membrane, which generates a novel cell adhesion strategy through active clamping.