To understand lens fiber cell elongation- and differentiation-associated cytoskeletal remodeling, here we identified and characterized the major protein components of lens fiber cell Triton X-100 insoluble fraction by mass spectrometry and immunoblot analysis. This analysis identified spectrin, filensin, vimentin, tubulin, phakinin, and P-actin as major cytoskeletal proteins in the lens fibers. Importantly, ezrin, radixin, and moesin (ERM), heat-shock cognate protein 70, and beta/gamma-crystallins were identified as major cytoskeletal-associated proteins. ERM proteins were confirmed to exist as active phosphorylated forms that exhibited intense distribution in the organelle free-zone fibers. Furthermore, ERM protein phosphorylation was found to be dramatically reduced in Rho GTPase-targeted transgenic mouse lenses. These data identify the ERM proteins, which cross-link the plasma membrane and actin, as major and stable cytoskeletal-associated proteins in lens fibers, and indicate a potential role(s) for the ERMs in fiber cell actin cytoskeletal and membrane organization. (c) 2008 Elsevier Inc. All rights reserved.