Response of radixin to perturbations of growth cone morphology and motility in chick sympathetic neurons in vitro.

The ERM protein--ezrin, radixin, moesin--localize to a variety of cortical structures, where they may participate in connecting the cytoskeleton to components of the plasma membrane. Antibodies that recognize the ERM proteins specifically stain growth cones of various neurons [Goslin et al., 1989: J. Cell Biol. 109:1621-1631; Birgbauer et al., 1991: J. Neurosci. Res. 30:232-241]. To probe the function of ERM proteins in growth cones, we studied the consequences of perturbing growth cone morphology and motility of cultured chick sympathetic neurons. We demonstrate that radixin is present in these growth cones. Withdrawal of nerve growth factor (NGF) induces rapid collapse of the growth cones; concomitantly, radixin staining in these growth cones are greatly diminished. Upon readdition of NGF, rapid growth cone formation is accompanied by relocalization of radixin. Induction of growth cone collapse by either growth cone-growth cone contact or exposure to brain membrane extract results in a similar diminution of radixin staining. We induced a more subtle change in the organization of the growth cones by subjecting them to an electric field. These growth cones rapidly orient toward the cathode. We show that the radixin staining of the growth cones is also asymmetrically localized toward the leading edges in the new direction of growth. The results suggest that the localization of radixin may be essential for the normal expression of growth cone morphology and function.