Analysis of a cortical cytoskeletal structure: a role for ezrin-radixin-moesin (ERM proteins) in the marginal band of chicken erythrocytes.

We are studying how the cytoskeleton determines cell shape, using a simple model system, the marginal band of chicken erythrocytes. We previously identified a minor component of the marginal band by a monoclonal antibody, called 13H9 (Birgbauer and Solomon (1989). J. Cell Biol. 109, 1609-1620; Goslin et al. (1989). J. Cell Biol. 109, 1621-1631). mAb 13H9 also binds to the leading edges of fibroblasts and to neuronal growth cones and recognizes the cytoskeletal protein ezrin. In recent years, two proteins with a high degree of homology to ezrin were identified: moesin and radixin, together comprising the ERM protein family. We now show that the contiguous epitope sufficient for mAb 13H9 binding is a sequence present in each of the ERM proteins, as well as the product of the gene associated with neurofibromatosis 2, merlin or schwannomin. We used biochemical and immunological techniques, as well as PCR to characterize the expression and localization of the ERM proteins in chicken erythrocytes. The results demonstrate that radixin is the major ERM protein associated with the cytoskeleton. Both ezrin and radixin localize to the position of the marginal band. Our results suggest that the ERM proteins play functionally conserved roles in quite diverse organelles.