Sostdc1, a secreted dual BMP and WNT antagonist, is differentially expressed in RCS rdy⁺ and rdy^- rat retinal pigment epithelial cells

Abstract

Purpose : we implemented an original strategy for identifying unknown secreted proteins by the rat retinal pigment epithelium.

Methods : we used the “signal peptide selection” method, based on a single step yeast genetic screening, which allows the selection of cDNAs encoding secreted and membrane-bound proteins sorted by the secretory apparatus of eye cells. A retinal pigment epithelium (RPE) cDNA library was cloned into a pSUC2 vector and screened using the yeast signal sequence trap system. Using this approach, we identified a unique full length cDNA encoding the rat Sostdc1 protein (NM_153737.1). Using this cDNA sequence, we performed immunohistochemistry experiments with anti-Sostdc1 antibodies. Semi-quantitative RT-PCR analysis, In situ hybridization, and immunohistochemistry experiments were carried out on post-natal retinal and cerebellar tissue sections of Royal College of Surgeon RCS rdy^- p⁺ and control congenic rats rdy⁺ p⁺.

Results : By triplicated RT-PCR, the cDNA encoding Sostdc1 was indeed detected in rat post-natal RPE and cerebellum as well as in various adult rat tissues.We analyzed Sostdc1 gene expression profile and Sostdc1 protein localization in normal RCS rdy⁺ and dystrophic RCS rdy^- rat retinas at various stages of post-natal ocular development as well as in adult RCS rdy⁺ and RCS rdy- brain tissue sections. Sostdc1 mRNA and protein were present in the control and dystrophic rat RPE cell monolayer at 14, 21 and 45 days after birth. The amount of Sostdc1 mRNA decreased between the 14th and 45th post-natal day in normal RCS rdy⁺ RPE. Interestingly, by semi-quantitative RT-PCR applied to total RNAs extracted from microdissected rat RPE and cerebellum, an increase of Sostdc1 mRNA was observed in the RPE and cerebellum of RCS rdy^- rats.

Conclusions : Sostdc1 is transactivated by the transcription factors Sox2 and Pax6. it is also expressed in the developing bones and teeth. No oculo-skeletal disease has been associated so far with mutations od SOSTDC1 in human patients nor in animal models. Human patients affected by retinal dystrophies or congenital abnormalities of the eye associated with cerebellar and/or skeletal abnormatities and/or teeth abnormalities should be screened for mutations in SOSDC1 gene.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.