Identification of a protein related to the S-antigen in choroid plexus in quails

Using monoclonal and polyclonal antibody immuno-fluorescence, various areas of the quail diencephalon were tested immunocytochemically for the presence of S-antigen, which is a regulatory protein of retinal photoreceptors. In adult quail and embryos (from day 13 until hatching), S-antigen immunoreactivity was demonstrated in the cytoplasm of epithelial cells in the choroid plexus of the third ventricle. Similar data have previously been obtained in quail retinal photoreceptors. No labeling could be seen in the other investigated diencephalic areas, including the hypothalamus. Although an extraocular photoregulation of the reproductive cycle has previously been reported in birds, further investigations are needed before it can be concluded that the choroid plexus of the third ventricle is involved in this or other types of regulation.