LENS TROPOMODULIN - DEVELOPMENTAL EXPRESSION DURING DIFFERENTIATION

Lens epithelial cells undergo a dramatic transformation during the pro cess of differentiation into elongated fiber cells. The membrane-assoc iated actin cytoskeleton is likely to play a critical role in the stab ilization and maintenance of the highly elongated fiber cell shape. Tr opomodulin is a tropomyos-inbinding protein associated with actin fila ments in a variety of terminally differentiated cell types where stabl e actin filament organization is required for cell function. We now pr esent results of studies to determine the temporal expression of tropo modulin in the developing lens. In situ hybridization experiments dete cted expression of tropomodulin mRNA in the developing mouse lens in e longating cells with a pattern similar to that of the fiber specific b eta- and gamma-crystallins. Tropomodulin mRNA expression first appeare d around 11.5 days post-coitum in elongating cells in the posterior pa rt of the lens vesicle. At later stages the signal for tropomodulin wa s present in the elongating cells at the lens equator and in cortical fiber cells; signal was absent from the epithelium. To investigate the possible link between tropomodulin expression and fiber differentiati on we used a well-established lens epithelial explant culture system i n which fiber differentiation is induced by fibroblast growth factor ( FGF). Tropomodulin expression was only observed in FGF-treated explant s in conjunction with morphologic changes characteristic of lens fiber cell differentiation. The appearance of tropomodulin during the proce ss of fiber cell differentiation suggests that tropomodulin may be imp ortant for stabilization and/or determination of actin filament length . (C) 1996 Academic Press Limited