Identification and localization of myosin superfamily members in fish retina and retinal pigmented epithelium.

Myosins are cytoskeletal motors critical for generating the forces necessary for establishing cell structure and mediating actin-dependent cell motility. In each cell type a multitude of myosins are expressed, each myosin contributing to aspects of morphogenesis, transport, or motility occurring in that cell type. To examine the roles of myosins in individual retinal cell types, we first used polymerase chain reaction (PCR) screening to identify myosins expressed in retina and retinal pigmented epithelium (RPE), followed by immunohistochemistry to examine the cellular and subcellular localizations of seven of these expressed myosins. In the myosin PCR screen of cDNA from striped bass retina and striped bass RPE, we amplified 17 distinct myosins from eight myosin classes from retinal cDNA and 11 distinct myosins from seven myosin classes from RPE cDNA. By using antibodies specific for myosins IIA, IIB, IIIA, IIIB, VI, VIIA, and IXB, we examined the localization patterns of these myosins in retinas and RPE of fish, and in isolated inner/outer segment fragments of green sunfish photoreceptors. Each of the myosins exhibited unique expression patterns in fish retina. Individual cell types expressed multiple myosin family members, some of which colocalized within a particular cell type. Because much is known about the functions and properties of these myosins from studies in other systems, their cellular and subcellular localization patterns in the retina help us understand which roles they might play in the vertebrate retina and RPE.