The bovine iris-ciliary epithelium expresses components of rod phototransduction

Earlier studies have documented that the iris in lower vertebrates is photosensitive. In the present work, we examined whether the bovine iris which exhibits a common embryonic origin with the ocular ciliary epithelium and the neural retina, expresses components of phototransduction. By Northern blot and RT-PCR amplification we detected in the iris, rhodopsin, rhodopsin kinase and arrestin transcripts and DNA products, respectively, of the same size as in the retina. By Western blot, antibodies to rhodopsin, rhodopsin kinase and arrestin detected low levels of protein with similar molecular masses as in the retina. Transient transfections of bovine iris cells in vitro with rhodopsin promoter-luciferase-reporter constructs (p130-Luc, p176-Luc, 1225-Luc and p2000-Luc) containing proximal and distal promoter elements led to a significant stimulation of promoter activity over the basal activity. In particular, the construct p225-Luc containing proximal promoter elements upstream of the transcription start site (-225 to +70 bp) led to 3.1-fold stimulation of activity over p176-Luc, 2.1-fold over p130 or p2000-Luc and 190-fold over the basal activity. These results suggested that the bovine iris cells contain factors that could either stimulate or attenuate rhodopsin transcription. The data also supported the view that components associated with non-visual phototransduction are expressed in extraretinal sites including the ciliary epithelium and the iris.