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S.N. Reid, D.B. Farber; Secretion and Transport of Retinoschisin, the Protein Product of the X-Linked Juvenile Retinoschisis Gene . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1535.
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Purpose: Retinoschisin is a small globular protein containing a putative secretory leader peptide and an adhesion FA5/8C-discoidin motif. Mutations in the gene that encodes retinoschisin cause X-linked juvenile retinoschisis, a degenerative disease of the retina. The secretory nature of this protein has been investigated by us earlier when we found that retinoschisin was released by photoreceptor-like Weri cells (Grayson et al., Human Mol. Genet. 9:1873-1879, 2000). The distribution of retinoschisin mRNA in the photoreceptor inner segments and outer nuclear layer but not inner retinal layers, in conjunction with the protein distribution throughout the retina (Reid et al., Gene 227:257-266, 1999; Grayson et al., 2000) also support the notion that retinoschisin is secreted by photoreceptor cells and then transported into the inner retina. In this study, we examined the secretion of retinoschisin by the retina, specifically by the photoreceptor cells, and the transport of retinoschisin into the inner retina. Methods: Whole retina, micro-dissected inner and outer retina, anterior segment, RPE/choriod/sclera and retinas of adult rd/rd mice (that contain only the inner retina) were cultured overnight. The culture media were harvested and subjected to Western blot analysis using anti-retinoschisin antibodies. To study retinoschisin transport, we either obtained or constructed the plasmids necessary to generate by in vitro transcription/translation the following recombinant proteins: green fluorescent protein (GFP), retinoschisin-GFP fusion protein (RS-GFP) and rod α-transducin-GFP fusion protein (RαT-GFP). We then incubated these proteins with retina explants. Results: Western blot analysis showed retinoschisin in the culture media of the retina and the photoreceptor-containing outer retina, but not in the culture media of the inner retina or other ocular tissues. The retina preferentially took up RS-GFP over GFP and RαT-GFP. Time-lapse experiments showed that in only 30 minutes RS-GFP appeared in Müller cells and the inner retina. Conclusions: Retinoschisin is secreted by photoreceptor cells and very quickly transported into the inner retina by Müller cells.
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