EZRIN IS CONCENTRATED IN THE APICAL MICROVILLI OF A WIDE VARIETY OF EPITHELIAL-CELLS WHEREAS MOESIN IS FOUND PRIMARILY IN ENDOTHELIAL-CELLS

Ezrin and moesin are two cytoskeletal proteins originally purified fro m human placenta that are 74% identical in overall protein sequence. T hey are believed to be membrane-cytoskeletal linking proteins because they share sequence homology with erythrocyte band 4.1 and colocalize with actin specifically in microvilli and membrane ruffles in cultured cells. To determine if ezrin and moesin share similar distributions i n vivo, we studied their localizations with respect to F-actin in tiss ue sections. Surprisingly, ezrin and moesin exhibited very different c ellular distributions. Ezrin was highly concentrated and colocalized w ith actin on the apical surface of many epithelial cell types. During enterocyte differentiation, the pattern of expression and redistributi on of ezrin was consistent with it performing a role in microvillus as sembly. Immunoelectron microscopy in differentiated cells revealed tha t ezrin was restricted mainly to the plasma membrane of microvilli and other actin-rich surface projections. Moesin was found in endothelial cells and was also enriched in the apical microvilli of a restricted set of epithelial cells. All polarized cell types with abundant microv illi contained one or both proteins, suggesting that ezrin and moesin perform related functions. However, the differential expression of ezr in and moesin indicates that they have distinct properties, which are uniquely adapted to specific cell types.