Expression of X-linked retinoschisis protein RS1 in photoreceptor and bipolar cells

PURPOSE. To examine the biochemical properties, cell expression, and locali zation of RS1, the product of the gene responsible for X-linked juvenile re tinoschisis. METHODS. Rs1h mRNA expression was measured from the eyes of wild-type and r d/rd mice by Northern blot analysis and reverse transcription-polymerase ch ain reaction (RT-PCR). Specific antibodies raised against the N terminus of RS1 were used as probes to examine the properties and distribution of RSI in retina, retinal cell cultures, and transfected COS-1 cells by Western bl ot analysis and immunofluorescence microscopy. RESULTS. Rs1h mRNA expression was detected in the retina of postnatal day(P )11 and adult CD1 mice, but not homozygous rd/rd mice by Northern blot anal ysis. However, Rs1h expression was detected in rd/rd mice by RT-PCR. RSI mi grated as a single 24-kDa polypeptide under disulfide-reducing conditions a nd a larger complex (>95 kDa) under nonreducing conditions in the membrane fraction of retinal tissue homogenates and transfected COS-1 cells. RSI ant ibodies specifically stained rod and cone photoreceptors and most bipolar c ells, but not Muller cells, ganglion cells, or the inner limiting membrane of adult and developing retina as revealed in double-labeling studies. RS1 antibodies also labeled retinal bipolar cells of photoreceptorless mice and retinal bipolar cells grown in cell culture. CONCLUSIONS. RSI is expressed and assembled in photoreceptors of the outer retina and bipolar cells of the inner retina as a disulfide-linked oligomer ic protein complex. The secreted complex associates with the surface of the se cells, where it may function as a cell adhesion protein to maintain the integrity of the central and peripheral retina.