IMMUNOHISTOCHEMICAL LOCALIZATION OF INHIBIN IN THE RETINAL INTERPHOTORECEPTOR MATRIX

Inhibin and its related proteins, the activins are widely distributed multifunctional members of the transforming growth factor beta (TGF be ta) superfamily, a group of proteins with a wide variety of growth- an d differentiation-regulating effects. Frozen sections of bovine retina were analysed immunohistochemically for inhibin using a specific poly clonal rabbit antibody generated against the N-terminal 30 amino acids of its alpha-subunit. Inhibin staining was selectively localized in t he portion of the neural retina occupied by photoreceptor cell inner a nd outer segments. Electron microscopic immunohistochemistry revealed that inhibin immunoreactivity was specifically localized in the interp hotoreceptor matrix but not in direct association with photoreceptor c ell cytoplasm or membrane. No staining was observed when the inhibin a ntiserum was absorbed with a synthetic inhibin alpha-subunit peptide; antisera to follistatin or prolactin showed no retinal immunoreactivit y. These observations demonstrate that inhibin is selectively localize d in the retinal interphotoreceptor matrix, suggesting a role for inhi bin as a growth or trophic factor for photoreceptor and/or pigmented e pithelial cells.