Distribution of R-cognin in late embryonic and post-hatching chicken retina.

The histological distribution of R-cognin in chick retinas was determined from embryonic day 8 through 13 wk post-hatching by indirect immunofluorescence using polyclonal anticognin. On embryonic day 8, at a developmental stage without distinct retina layers, most of the cells within the tissue exhibited fluorescence. By embryonic day 12, when the strata of the retina are delineating and initial synapses are beginning to form, R-cognin fluorescence became concentrated in the nascent ganglion cell, and to a lesser extent, inner nuclear layers. By embryonic day 16 (extending through post-hatching day 26), the staining of R-cognin was specific for the ganglion cell and nerve fiber layers. Fluorescence was prominent on the cell somal membranes but also was present on the processes of these cells at the ganglion cell layer-inner plexiform layer interface. Pre-immune serum and anticognin after preabsorption with R-cognin exhibited no fluorescence. The results demonstrated that the known decrease in R-cognin found in the retina during the latter half of embryonic development in the chick is not uniform across the retina, but that R-cognin is preferentially retained on cells within the ganglion cell layer. While cells within the ganglion cell layer also exhibit alpha-bungarotoxin binding, the majority of the latter is found in the inner plexiform layer. Thus, the observations are consistent with a role for R-cognin in the formation or maintenance of functional cell-cell connections within the entire retina prior to developmental day 11, or in retinal ganglion cell layer formation or stability subsequent to embryonic day 11.