A nonsense mutation in Gnat1, encoding the α subunit of rod transducin, in spontaneous mouse models of retinal dysfunction

ICR-derived retinal dysfunction (IRD) 1 and IRD2 mice are new spontaneous mouse models of rod-cone and rod dysfunctions, respectively. In this study, we investigated the cause of rod dysfunction in IRD1 and IRD2 mice. Gene expression of rod phototransduction proteins was analyzed by quantitative real-time RT-PCR. mRNA levels of Gnat1, which encodes the α subunit of rod transducin (Trα), were severely reduced. Trα protein was immunohistochemically undetectable in both IRD1 and IRD2 mice. Sequencing of Trα cDNA revealed a 48-base pair (bp) insertion between exons 4 and 5 in both mutant strains. The insertion changed codon 150 (TAC) to a stop codon (TAG) (Tyr150Ter). The truncated Trα protein was undetectable in the retinas of both mutants by western blot analysis using a primary antibody against the N-terminal region. A 57-bp deletion was identified in intron 4 of the Gnat1 gene, which encodes the Trα protein, and included the last two bases of the splice donor site of intron 4. Thus our results showed that IRD1 and IRD2 mice harbor a nonsense mutation in the Gnat1 gene, resulting in the absence or suppressed expression of the Trα protein, which is the likely cause of rod dysfunction in both mutants.