title: Redundant contribution of a Transient Receptor Potential cation channel Member 1 exon 11 single nucleotide polymorphism to equine congenital stationary night blindness.
abstract: BACKGROUND
  Congenital stationary night-blindness (CSNB) is a recessive autosomal defect in low-light vision in Appaloosa and other horse breeds. This condition has been mapped by linkage analysis to a gene coding for the Transient Receptor Potential cation channel Member 1 (TRPM1). TRPM1 is normally expressed in the ON-bipolar cells of the inner nuclear layer of the retina. Down-regulation of TRPM1 expression in CSNB results from a transposon-like insertion in intron 1 of the TRPM1 gene. Stop transcription signals in this transposon significantly reduce TRPM1 primary transcript levels in CSNB horses. This study describes additional contributions by a second mutation of the TRPM1 gene, the ECA1 108,249,293 C > T SNP, to down-regulation of transcription of the TRPM1 gene in night-blind horses. This TRPM1 SNP introduces a consensus binding site for neuro-oncological ventral antigen 1 (Nova-1) protein in the primary transcript. Nova-1 binding disrupts normal splicing signals, producing unstable, non-functional mRNA transcripts.
  
  
  RESULTS
  Retinal bipolar cells express both TRPM1 and Nova-1 proteins. In vitro addition of Nova-1 protein retards electrophoretic migration of TRPM1 RNA containing the ECA1 108,249,293 C > T SNP. Up-regulating Nova-1 expression in primary cultures of choroidal melanocytes carrying the intron 11 SNP caused an average log 2-fold reduction of ~6 (64-fold) of TRPM1 mRNA expression.
  
  
  CONCLUSIONS
  These finding suggest that the equine TRPM1 SNP can act independently to reduce survival of TRPM1 mRNA escaping the intron 1 transcriptional stop signals in CSNB horses. Coexistence and co-inheritance of two independent TRPM1 mutations across 1000 equine generations suggests a selective advantage for the apparently deleterious CSNB trait.
authors.affiliation: Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Scott
authors.affiliation: Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada.
authors.forename: Emily E
authors.initials: EE
authors.lastname: John
authors.affiliation: Department of Biology, University of Tampa, Tampa, FL, 33606, USA.
authors.forename: Rebecca R
authors.initials: RR
authors.lastname: Bellone
authors.affiliation: Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada.
authors.forename: John C H
authors.initials: JC
authors.lastname: Ching
authors.affiliation: Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Loewen
authors.affiliation: Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada.
authors.forename: Lynne S
authors.initials: LS
authors.lastname: Sandmeyer
authors.affiliation: Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada.
authors.forename: Bruce H
authors.initials: BH
authors.lastname: Grahn
authors.affiliation: Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada. george.forsyth@usask.ca.
authors.forename: George W
authors.initials: GW
authors.lastname: Forsyth
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D005091:Exons; D015785:Eye Diseases, Hereditary / Q000235:genetics / Q000662:veterinary*; D040181:Genetic Diseases, X-Linked / Q000235:genetics / Q000662:veterinary*; D006734:Horse Diseases / Q000235:genetics*; D006736:Horses; D009216:Myopia / Q000235:genetics / Q000662:veterinary*; D009419:Nerve Tissue Proteins / Q000235:genetics; D000090682:Neuro-Oncological Ventral Antigen; D009755:Night Blindness / Q000235:genetics / Q000662:veterinary*; D020641:Polymorphism, Single Nucleotide; D012313:RNA / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics; D050053:TRPM Cation Channels / Q000235:genetics*
chemical_list: D009419:Nerve Tissue Proteins; D000090682:Neuro-Oncological Ventral Antigen; D016601:RNA-Binding Proteins; D050053:TRPM Cation Channels; D012313:RNA
keywords: Appaloosa; Congenital stationary night blindness; Transient Receptor Potential cation channel Member 1