Trpm1 Point Mutation Underlies Retinal Dysfunction In The Mtvr27 Mouse Model Of Complete Congenital Stationary Night Blindness

Abstract

Purpose: : Using an ERG screen of ENU-mutagenized C57BL/6J mice to identify new vision mutants, mutant Mtvr27 was identified due to the absence of the b-wave component while the a-wave was present. Here we identify the gene involved and define the retinal phenotype of the mutant.

Methods: : Linkage mapping, complementation mating, and candidate gene sequencing identified the Mtvr27 gene. Retinal electrophysiology was evaluated by ERG, whole cell patch clamp analysis of bipolar cell responses to a glutamate agonist in an in vitro slice preparation and in vivo RGC single cell electrophysiology. Retinal anatomy was evaluated by immunohistochemistry and confocal microscopy.

Results: : The Mtvr27 locus mapped to a region of Chr. 7 that contains Trpm1. Offspring generated by crossing Mtvr27 and Trpm1^-/- mice had a normal ERG a-wave but no b-wave indicating that Mtvr27 is a new Trpm1 allele. A point mutation (Ala952Thr) was identified in Trpm1^Mtvr27. Overall retinal structure appears normal in Trpm1^Mtvr27 mice. A rabbit polyclonal antibody against TRPM1 (Sigma) labels the OPL in Trpm1^Mtvr27 but not Trpm1^-/- retina. Trpm1^Mtvr27 DBCs do not respond to puffs of the mGluR6 antagonist LY341495. Differences are found in the light evoked responses of Trpm1^Mtvr27 RGCs when compared to C57B6/J RGCs that include abnormal receptive field organization and the presence of spontaneous rhythmic bursting. Dark-adapted ERGs of Trpm1^Mtvr27 mice contain a small low intensity response that is absent in Trpm1^-/- animals.

Conclusions: : The Mtvr27 mutant is caused by a mutation in the Trpm1 gene. The phenotype of Trpm1^Mtvr27mutant mice resembles that of the Trpm1^-/- in many ways, but is distinguished by the retention of TRPM1 protein expression in the OPL and a residual ERG response at low intensities.

Keywords: bipolar cells • inner retina dysfunction: hereditary • electrophysiology: non-clinical