Bestrophin Gene Mutations Cause Canine Multifocal Retinopathy: A Novel Animal Model for Best Disease

PURPOSE. Canine multifocal retinopathy (cmr) is an autosomal recessive disorder of multiple dog breeds. The disease shares a number of clinical and pathologic similarities with Best macular dystrophy (BMD), and cmr is proposed as a new large animal model for Best disease. METHODS. cmr was characterized by ophthalmoscopy and histopathology and compared with BMD-affected patients. BEST1 (alias VMD2), the bestrophin gene causally associated with BMD, was evaluated in the dog. Canine ortholog cDNA sequence was cloned and verified using RPE/choroid 5′- and 3′-RACE. Expression of the canine gene transcripts and protein was analyzed by Northern and Western blotting and immunocytochemistry. All exons and the flanking splice junctions were screened by direct sequencing. RESULTS. The clinical phenotype and pathology of cmr closely resemble lesions of BMD. Canine VMD2 spans 13.7 kb of genomic DNA on CFA18 and shows a high level of conservation among eukaryotes. The transcript is predominantly expressed in RPE/choroid and encodes bestrophin, a 580-amino acid protein of 66 kDa. Immunocytochemistry of normal canine retina demonstrated specific localization of protein to the RPE basolateral plasma membranes. Two disease-specific sequence alterations were identified in the canine VMD2 gene: a C73T stop mutation in cmr1 and a G482A missense mutation in cmr2. CONCLUSIONS. The authors propose these two spontaneous mutations in the canine VMD2 gene, which cause cmr, as the first naturally occurring animal model of BMD. Further development of the cmr models will permit elucidation of the complex molecular mechanism of these retinopathies and the development of potential therapies

Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and leopard complex spotting in the horse

Leopard complex spotting is a group of white spotting patterns in horses caused by an incompletely dominant gene (LP) where homozygotes (LP/LP) are also affected with congenital stationary night blindness. Previous studies implicated Transient Receptor Potential Cation Channel, Subfamily M, Member 1 (TRPM1) as the best candidate gene for both CSNB and LP. RNA-Seq data pinpointed a 1378 bp insertion in intron 1 of TRPM1 as the potential cause. This insertion, a long terminal repeat (LTR) of an endogenous retrovirus, was completely associated with LP, testing 511 horses (χ²=1022.00, p<<0.0005), and CSNB, testing 43 horses (χ2=43, p<<0.0005). The LTR was shown to disrupt TRPM1 transcription by premature poly-adenylation. Furthermore, while deleterious transposable element insertions should be quickly selected against the identification of this insertion in three ancient DNA samples suggests it has been maintained in the horse gene pool for at least 17,000 years. This study represents the first description of an LTR insertion being associated with both a pigmentation phenotype and an eye disorder.Rebecca R. Bellone … David L. Adelson, Sim Lin Lim … et al