Structural and functional analysis of Drosophila Moesin. O. Nikiforova , R.G. Fehon. Biology Department and University Program in Genetics, Duke University, Durham, NC.

   A dynamic organization of cortical actin filaments is important for many membrane-based biological processes such as cell adhesion, cytokinesis, cell shape maintenance, motility, and many others. Ezrin, Radixin, and Moesin (ERM), a group of closely related actin proteins within the Protein 4.1 superfamily, have been traditionally thought of as static cross-linkers between cortical cytoskeleton and plasma membrane because of their ability to associate with the cytoplasmic tails of integral membrane proteins and actin filaments. Recently, this view has expanded to include the notion that ERM may participate in a major signaling pathway involved in reorganizing actin filaments, the Rho signaling pathway. Evidence from several different research groups has placed ERM upstream as well as downstream of Rho.
   Consistent with the cross-linking function, the ERM proteins have been shown to be involved in the formation of actin-based cell surface structures in mammalian cell culture. However, a thorough loss-of-function analysis has been impeded by the fact that the three mammalian proteins are functionally redundant. In contrast, Drosophila has only one member of the ERM group, Moesin. We show here that cells that lose Moesin function undergo an epithelial-to-mesenchymal transition, accompanied by loss of junctional markers and apico-basal polarity. At the same time, filamentous actin undergoes dramatic redistribution. We also examine the consequences of removing the actin-binding domain in Moesin and investigate the relationship between Moesin and the Rho signaling pathway.