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Elise Orhan, Laurent Prezeau, Christelle Michiels, Claire Vol, Jose Sahel, Isabelle Audo, Christina Zeitz; Elucidation of physiopathological mechanisms of GPR179. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5088.
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© ARVO (1962-2015); The Authors (2016-present)
Complete congenital stationary night blindness (cCSNB) is a heterogeneous retinal disorder characterized by visual impairment in dim light conditions. This disorder is due to a signal transmission defect from photoreceptors to adjacent bipolar cells in the retina. Mutations in GPR179 lead to one form of autosomal recessive cCSNB. The gene is expressed in the inner nuclear layer and the respective protein localizes in the dendritic tips of bipolar cells in the retina. Similar patterns have been observed for other genes and proteins implicated in cCSNB. The mutation spectrum comprises nonsense, frameshift, missense and splice site mutations. Although nonsense and frameshift mutations are predicted to lead to nonsense mediated mRNA decay or non-functional truncated proteins, pathogenic mechanisms of missense and splice site mutations are unclear. The purpose of our study was to further investigate these mechanisms.
Live-cell extracellular with subsequent intracellular immunolocalization and ELISA studies were performed on COS-1 cells after transient tranfection either with wild-type or missense mutated GPR179 constructs. For the splice-site mutation, a wt and mutated (c.1784+1G>A) mini-gene constructs were transiently transfected and RNA extracted. After RT-PCR, amplified products were cloned and Sanger sequenced.
Our immunolocalization and ELISA studies showed that three out of four described missense mutations (p.Tyr220Cys, p.Gly455Asp and p.His603Tyr) lead to severely reduced surface protein, while the most N-terminally located missense mutation (p.Asp126His) does not significantly alter surface localization. RT-PCR performed on wild-type and mutated mini-gene show that the mutated splice donor site alter GPR179 splicing.
Here we elucidated the pathogenic mechanism of almost all missense and splice site mutations in GPR179 identified so far. These findings indicate that this form of cCSNB is presumably due to loss of GPR179 protein function. Pathogenic mechanism(s) associated with N-terminus mutant needs to be further investigated.
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