Localization of alpha integrin subunits in the neural retina of the tiger salamander

Background: Integrin receptors mediate cell-extracellular matrix interactio ns and regulate many events, including cell growth, proliferation, and diff erentiation. Retinal integrins are incompletely understood, although these receptors are potentially important factors in normal retinal function and pathology. Methods: Immunocytochemistry was used to localize alpha integrin subunits la in the neural retina. Results: Each alpha integrin subunit had a unique distribution in the retina, although there was considerable overl ap among subunits. The alpha1 subunit was broadly distributed throughout th e retina, with some presumptive ganglion cells showing enriched labeling. T he alpha2 subunit was present on all retinal cell bodies, but was reduced i n synaptic layers. The alpha3 subunit was present in synaptic layers, Mulle r cells, and some cone and amacrine cells. The alpha4 subunit was broadly d istributed in the nuclear Layers but was reduced in synaptic layers. The al pha5 subunit was broadly expressed in the nuclear and synaptic layers with enriched labeling in the outer plexiform layer. Labeling for the alpha6 sub unit was restricted to the outer limiting membrane and some cone outer segm ents. Double-labeling studies indicated that photoreceptor terminals may ex hibit alpha1 and alpha5 subunits, while processes from second-order neurons may exhibit alpha1, alpha3, and alpha5 subunits. Conclusion: Integrin rece ptors containing the alpha1, alpha3, and alpha5 subunits may have important functions at retinal synapses, in addition to roles in the nuclear layers. Integrin receptors containing alpha2, alpha4, and alpha6 subunits probably serve non-synaptic functions.