Changes in the immunoreactivity for inhibin in mouse retina during development of photoreceptor cells

Inhibin, a widely distributed, multifunctional member of the transforming growth factor beta superfamily, was originally isolated from ovarian follicular fluid. This molecule was recently localized in bovine and rat retina by immunohistochemistry and the mRNA encoding the alpha-subunit of inhibin was detected in the retina by in situ hybridization and the reverse transcription polymerase chain reaction. In this study we have examined, by immunohistochemical methods, the distribution pattern of inhibin in developing mouse eyes on days 10, 11, 14, 16, 18 of gestation (E0 = coitus) and postnatal days 0, 2, 4, 6, 8, 12, 16 and 18 of age (P0 = day of birth). Immunoreactivity for inhibin appeared on E10 (the earliest day of gestation examined) in the lens and in migrating large cells between the lens and the inner layer of the optic cup (future neurons of retina). On E16, cells located in the neuroblastic layer were stained. At birth (P0), the ganglion cells were heavily stained and some amacrine cells were weakly stained. By P4, the amacrine and bipolar cells were positively stained. The inner plexiform layer was heavily stained and the outer plexiform layer and horizontal cells were also apparent and stained. From P6 on, inhibin-immunoreactive staining was localized at the inner segment of the photoreceptor layer, and to ganglion cells in the inner nuclear layer (INL). By P12, ganglion cells, INL, and inner segments of the photoreceptor layer were heavily stained. The outer segments of the photoreceptor layer, presumably the interphotoreceptor matrix, were strongly stained with antibodies against the alpha-subunit, whereas the outer and inner plexiform layers were also moderately stained. The staining in the INL generally decreased with progressing age. We conclude that inhibin is expressed in the eye cup as early as day 10 of gestation, migrates toward the direction of pigmented epithelial layers and is concentrated in the interphotoreceptor matrix by P12, which showed a distribution pattern similar to that of the adult mouse. These findings suggest that inhibin may play a role in the development of the eye cup and the retina.