Presence of the Gpr179^nob5 mutation in C3H-derived transgenic mice

Abstract

Purpose: Congenital stationary night blindness (CSNB) is a disease caused by impaired photoreceptor transmission and results in reduced visual acuity. In the complete form CSNB, and its animal models, the ERG has a no b-wave (nob) phenotype in which the component generated by depolarizing bipolar cells (DBC) is absent. Our ERG studies of erythropoietin (EPO) transgenic mice generated on a C3H/C57BL6 background (tg21) displayed a nob phenotype. In the present study we demonstrate that this is due to the Gpr179^nob5 mutation that appears to be broadly associated with the C3H genetic background.

Methods: We studied tg21 mice which over-express EPO in the brain and retina, wild type controls, and another mouse line (tg6) over-expressing EPO systemically. ERG analyses were obtained under dark- and light-adapted conditions. Immunohistochemistry was performed using an antibody against PKCα. Inverse PCR was carried out to identify the insertion site of the EPO transgene. Taqman RT-PCR assays were used to investigate whether tg21 involves a known mutation or a new gene required for DBC function.

Results: Tg21 mice had a nob ERG phenotype under dark- and light-adapted conditions, whereas the b-wave was present in non-transgenic controls. The b-wave was also present in tg6 transgenic mice, indicating that overexpression of EPO did not impair DBC function. DBC structure was normal in nob mice. The insertion site of the EPO construct was mapped to chromosome 8. RT PCR experiments revealed that tg21 nob mice lack expression of Gpr179, a G-protein coupled receptor essential for DBC signal transduction located on chromosome 11. PCR analysis of tg21 DNA confirmed the presence of the recently described Gpr179^nob5 insertional mutation in intron 1 of Gpr179.

Conclusions: The loss of the ERG b-wave observed originally in tg21 transgenic mice is not a consequence of EPO overexpression but instead reflects the Gpr179^nob5 mutation. Current efforts are targeted towards understanding the extent to which the Gpr179^nob5 allele is present in C3H sublines.

Keywords: 435 bipolar cells • 691 retina: proximal (bipolar, amacrine, and ganglion cells) • 510 electroretinography: non-clinical