A Large Animal Model for CNGB1 Autosomal Recessive Retinitis Pigmentosa

Abstract

Retinal dystrophies in dogs are invaluable models of human disease. Progressive retinal atrophy (PRA) is the canine equivalent of retinitis pigmentosa (RP). Similar to RP, PRA is a genetically heterogenous condition. We investigated PRA in the Papillon breed of dog using homozygosity mapping and haplotype construction of single nucleotide polymorphisms within a small family group to identify potential positional candidate genes. Based on the phenotypic similarities between the PRA-affected Papillons, mouse models and human patients, CNGB1 was selected as the most promising positional candidate gene. CNGB1 was sequenced and a complex mutation consisting of the combination of a one basepair deletion and a 6 basepair insertion was identified in exon 26 (c.2387delA;2389_2390insAGCTAC) leading to a frameshift and premature stop codon. Immunohistochemistry (IHC) of pre-degenerate retinal sections from a young affected dog showed absence of labeling using a C-terminal CNGB1 antibody. Whereas an antibody directed against the N-terminus of the protein, which also recognizes the glutamic acid rich proteins arising from alternative splicing of the CNGB1 transcript (upstream of the premature stop codon), labeled rod outer segments. CNGB1 combines with CNGA1 to form the rod cyclic nucleotide gated channel and previous studies have shown the requirement of CNGB1 for normal targeting of CNGA1 to the rod outer segment. In keeping with these previous observations, IHC showed a lack of detectable CNGA1 protein in the rod outer segments of the affected dog. A population study did not identify the CNGB1 mutation in PRA-affected dogs in other breeds and documented that the CNGB1 mutation accounts for ∼70% of cases of Papillon PRA in our PRA-affected canine DNA bank. CNGB1 mutations are one cause of autosomal recessive RP making the CNGB1 mutant dog a valuable large animal model of the condition.

Assessment of Rod, Cone, and Intrinsically Photosensitive Retinal Ganglion Cell Contributions to the Canine Chromatic Pupillary Response

“…Diseases included CNGB1 -progressive retinal atrophy (PRA), CNGB3 achromatopsia (ACHM), PDE6B rod/cone dysplasia 1 (rcd1), RD3 rod/cone dysplasia 2 (rcd2), PDE6A rod/cone dysplasia 3 (rcd3), RPE65 Leber congenital amaurosis (LCA), PRCD progressive rod/cone degeneration (prcd), IQCB1 cone/rod dystrophy 2 (crd2), RPGR -X-linked progressive retinal atrophy 2 (XLPRA2), STK38L early retinal degeneration (erd), and NEHJ1 Collie eye anomaly (CEA). 16–39 Dogs were grouped and tested based on 4 previously reported retinal and optic nerve disease phenotypes, as follows: (1) Group 1 consisted of primary loss of rod function in dogs with CNGB1 -PRA and young (<1 year of age) dogs with PDE6A -rcd3 and PDE6B -rcd1; (2) group 2 included primary loss of cone function in dogs with CNGB3 -ACHM; (3) group 3 contained various severities of combined loss of rod and cone function in older dogs affected with PDE6B -rcd1, RD3 -rcd2, and PDE6A -rcd3, and dogs affected with RPE65 -LCA, PRCD -prcd, IQCB1 -crd2, STK38L -erd, and RPGR -XLPRA2; (4) and group 4 included primary loss of optic nerve function in 1 dog with severe optic nerve head coloboma due to NEHJ1 -CEA, which was also affected by RD3 -rcd2. We also assessed pupillary responses to differential blue and red light intensities in 2 additional WT and 2 CNGB3 -mutant dogs.…”

Organization of cGMP sensing structures on the rod photoreceptor outer segment plasma membrane

“…While CNGA1 can be targeted to the plasma membrane in cultured cells, 35,36 it failed to localize to the OS in dog and mouse models lacking functional CNGB1. 34,37,38 Therefore, CNGA1 itself does not contain sufficient information for the OS targeting in rod photoreceptor cells in vivo. Location of the OS targeting signal in CNGB1 is under active debate, and accordingly 2 hypotheses were previously tested.…”

Genetics of eye disorders in the dog.

“…CNGB1 combines with CNGA1 to form the rod cyclic nucleotide gated channel. Previous studies have shown the requirement of CNGB1 for normal targeting of CNGA1 to the rod outer segment [16] and indeed the authors were able to demonstrate a lack of detectable CNGA1 protein in the rod outer segments of the affected Papillons homozygous for the mutation [15]. The same mutation was also described in Phalene dogs by Ahonen and collegues [17].…”

“…Retinal disorders can be categorized in various ways and the way in which they have been Cone-rod dystrophy CRD3 ADAM9 Glen of Imaal terrier [53,54] Primary open angle glaucoma POAG ADAMTS10 Beagle [147] Primary lens luxation PLL ADAMTS17 Multiple, mainly terrier breeds [129,132] Rod cone degeneration RCD4 C2orf71 Gordon Setter, Irish Setter, Tibetan Terrier [30] Generalised progressive retinal atrophy gPRA CCDC66 Schappendoes [28] Progressive retinal atrophy PRA CNGB1 Papillon [15,17] Cone degeneration CD CNGB3 Alaskan malamute [68] Cone degeneration CD CNGB3 German shorthaired pointer [69] Dwarfism with retinal dysplasia (oculoskeletal dysplasia) DRD2 (OSD2) COL9A2 Samoyed [90] Dwarfism with retinal dysplasia (oculoskeletal dysplasia) DRD1 (OSD1) COL9A3 Labrador retriever [90] Hereditary cataract HC, EHC HSF4 Staffordshire bull terrier, Boston terrier, French bulldog [103] Hereditary cataract HC HSF4 Australian Shepherd [107] Collie eye anomaly CEA NHEJ1 Collies [91] Cone-rod dystrophy NPHP4 Standard wirehaired dachshund [49] Photoreceptor dysplasia PD PDC Miniature schnauzer [13] Rod cone dysplasia RCD1 PDE6B Irish setter [2] Rod cone dysplasia RCD1 PDE6B Sloughi [3] Rod cone dysplasia RCD3 PDE6A Cardigan Welsh corgi [4] Progressive rod-cone degeneration PRCD PRCD Multiple breeds [23] Rod cone dysplasia RCD2 RD3 Collie [7] Autosomal dominant progressive retinal atrophy ADPRA RHO English mastiff [24] Congenital stationary night blindness CSNB RPE65 Briard [58,59] X-linked progressive retinal atrophy XLPRA2 RPGR Mixed breed dogs [18] X-linked progressive retinal atrophy XLPRA1 RPGR Siberian Husky, Samoyed [18] Cone-rod dystrophy CORD1 (CRD4) RPGRIP Dachshunds [38] Early retinal degeneration ERD STK38L Norwegian elkhound [11] Canine multifocal retinopathy CMR1…”