The beaded intermediate filaments and their potential functions in eye lens

The elongated fiber cells of the eye lens contain a unique cytoskeletal system, the beaded chain filaments (BFs). The BFs had been morphologically identified more than two decades ago, but the precise identity of their subunit molecules remained unknown. Recently, use of recombinant DNA approaches, refined morphological and immunochemical studies and experiments with mutant mice have allowed the molecular dissection of these structures and provided clues about their potential functins. The BFs represent a highly specialized network of intermediate filaments (IFs) juxtaposed to the plasma membrane. They are obligate heteropolymers composed of two lens‐specific polypeptides, filensin and phakinin. In this review we discuss the properties, molecular interactions and in situ arrangement of these two proteins, and comment on their potential roles during lens development.