Retinal S-antigen: immunocytochemical and immunochemical studies on distribution in animal photoreceptors and pineal organs.

Antiserum against bovine retinal S-antigen, a soluble protein (MW = 50 kDa) thought to be involved in phototransduction, was used in an immunohistochemical and immunochemical study of vertebrate eyes and pineal systems and invertebrate photoreceptor organs. Positive reactions, not seen with antiserum preabsorbed with highly purified S-antigen, were observed in planarian and starfish ocelli; scallop eyes; polychaete eye; crayfish compound eye; lamprey, salmon, frog, turtle, quail and hamster eyes. A specific reaction was also seen in the pineal organ of all the vertebrates examined, albeit weak in turtle and quail. In addition, several structures associated with photoreceptor organs, including the reduced frontal eyes of crayfish, the organ of Bellonci in crayfish eyestalk, and bipolar cells resembling those giving rise to Landolt's clubs in quail and golden hamster retinae, were immunopositive. Immunochemical studies revealed the presence of a single immunopositive band of protein which was similar but not identical in size in all vertebrate eyes and pineal organs (except that of chicken pineal) and invertebrate tissue examined. The wide distribution of positive reaction in photoreceptive tissue indicates that the retinal S-antigen determinant has been highly conserved during evolution.