Expression of X-linked retinoschisis protein RS1 in photoreceptor and bipolar cells.
OBJECTIVE
To examine the biochemical properties, cell expression, and localization of RS1, the product of the gene responsible for X-linked juvenile retinoschisis.


METHODS
Rs1h mRNA expression was measured from the eyes of wild-type and rd/rd mice by Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR). Specific antibodies raised against the N terminus of RS1 were used as probes to examine the properties and distribution of RS1 in retina, retinal cell cultures, and transfected COS-1 cells by Western blot 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 analysis. However, Rs1h expression was detected in rd/rd mice by RT-PCR. RS1 migrated as a single 24-kDa polypeptide under disulfide-reducing conditions and a larger complex (>95 kDa) under nonreducing conditions in the membrane fraction of retinal tissue homogenates and transfected COS-1 cells. RS1 antibodies specifically stained rod and cone photoreceptors and most bipolar cells, but not Müller 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
RS1 is expressed and assembled in photoreceptors of the outer retina and bipolar cells of the inner retina as a disulfide-linked oligomeric protein complex. The secreted complex associates with the surface of these cells, where it may function as a cell adhesion protein to maintain the integrity of the central and peripheral retina.
Department of Biochemistry and Molecular Biology, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada.
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D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D019556:COS Cells; D002522:Chlorocebus aethiops; D005136:Eye Proteins / Q000096:biosynthesis / Q000235:genetics*; D015870:Gene Expression; D008040:Genetic Linkage; D006801:Humans; D007395:Interneurons / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008817:Mice, Mutant Strains; D008856:Microscopy, Fluorescence; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D012162:Retinal Degeneration / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014960:X Chromosome / Q000235:genetics
D005136:Eye Proteins; D012333:RNA, Messenger; C108726:RS1 protein, human