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Thomas A. Ray, Nazarul Hasan, Maureen A. McCall, Gianluca Tosini, Patsy M. Nishina, Neal S. Peachey, Ronald G. Gregg; GPR179, An Orphan G Protein-Coupled Receptor, Is Critical To Depolarizing Cell Function And Interacts With GRM6. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3156.
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© ARVO (1962-2015); The Authors (2016-present)
Complete congenital stationary night blindness (cCSNB) is caused by a disruption in signaling in depolarizing bipolar cells (DBCs) and results in non-progressive impairment of night vision. A new mouse model of cCSNB, nob5, was identified based on a no b-wave ERG phenotype that was inherited as an autosomal recessive trait. The nob5 mouse does not have mutations in genes known to be critical for DBC function (Grm6, Nyx, Trpm1, Gnb5, Gnao1). We have identified the mutation underlying the nob5 phenotype and have begun to characterize the function of GPR179, the encoded protein.
The nob5 allele was mapped to a 1.4Mb region flanked by D11Mit67 and D11Mit14. Genomic sequence capture followed by next generation sequencing was utilized to identify the causative mutation. Antibodies to GPR179 were generated using peptide immunization in sheep, and used to characterize the expression pattern of this protein in retina. Immunohistochemistry was used to localize GPR179 in relation to other proteins critical to DBC function. Expression of mRNA was determined using by qRT-PCR. Interaction of GPR179 with GRM6 was determined using in vitro expression in mammalian cell lines.
Next generation sequencing identified the nob5 mutation as a transposon-like insertion in intron 1 of Gpr179. The insertion causes an ~800 fold decrease of Gpr179 mRNA expression in nob5 as compared to WT retina. Immunohistochemistry using an antibody to GPR179 shows the protein localizes to the DBC dendritic tips in WT mice. Expression was absent in the nob5 retina. Double-labeling of GPR179 and GRM6 show they co-localize in the WT retina. Expression of GPR179 and GRM6 in HEK293T cells and subsequent immunoprecipitation indicate they interact. While nob5 retinas retain GRM6 and TRPM1 expression, GPR179 is absent in retinas of Trpm1-/- and Grm6-/- mice.
GPR179 is an orphan G protein-coupled receptor that interacts with GRM6 and is part of a protein network responsible for DBC signal transduction.
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