Ezrin promotes morphogenesis of apical microvilli and basal infoldings in retinal pigment epithelium

Ezrin, a member of the ezrin/radixin/moesin (ERM) family, localizes to micr ovilli of epithelia in vivo, where it bridges actin filaments and plasma me mbrane proteins. Here, we demonstrate two specific morphogenetic roles of e zrin in the retinal pigment epithelium (RPE), i.e., the formation of very l ong apical microvilli and of elaborate basal infoldings typical of these ce lls, and characterize the role of ezrin in these processes using antisense and transfection approaches. In the adult rat RPE, only ezrin (no moesin or radixin) was detected at high levels by immunofluorescence and immunoelect ron microscopy at microvilli and basal infoldings. At the time when these m orphological differentiations develop, in the first two weeks after birth, ezrin levels increased fourfold to adult levels. Addition of ezrin antisens e oligonucleotides to primary cultures of rat RPE drastically decreased bot h apical microvilli and basal infoldings. Transfection of ezrin cDNA into t he RPE-J cell line, which has only trace amounts of ezrin and moesin, spars e and stubby apical microvilli, and no basal infoldings, induced maturation of microvilli and the formation of basal infoldings without changing moesi n expression levels. Taken together, the results indicate that ezrin is a m ajor determinant in the maturation of surface differentiations of RPE indep endently of other ERM family members.