title: A naturally occurring mouse model of achromatopsia: characterization of the mutation in cone transducin and subsequent retinal phenotype.
abstract: OBJECTIVE
  This work investigates a novel, naturally occurring mouse model of achromatopsia. The specific missense mutation within the Gnat2 gene was identified and the subsequent retinal phenotype characterized.
  
  
  METHODS
  The Gnat2 sequence was amplified using PCR from BALB/c and Gnat2(c.518A>G) retinae and the product sequenced. Retinal function was assessed at 3, 6, 9, and 12 months using the electroretinogram. Transducin and opsin expression were assessed at 3 and 12 months using immunohistochemistry and quantitative PCR. Retinal remodeling and Müller cell gliosis were investigated using immunocytochemistry.
  
  
  RESULTS
  An A to G missense mutation at position 518 of the Gnat2 gene was identified that resulted in an aspartic acid to glycine substitution. Gnat2(c.518A>G) animals showed no cone response, while the rod response was normal except for a decrease in the photoreceptor response at 12 months (a-wave, -14%). Gnat2(c.518A>G) retinal sections showed no transducin immunolabeling; however, protein was detected via Western blot. Gnat2 gene expression was only decreased at 12 months of age (-27%). There was reduced cone number at 12 months (-27%) and M-opsin showed evidence of mislocalization. Displaced photoreceptor terminals and altered horizontal cell, cone/rod bipolar cell morphology were evident at 3 months, becoming more extensive at 12 months with the emergence of Müller cell gliosis.
  
  
  CONCLUSIONS
  The Gnat2(c.518A>G) mouse contains a missense mutation that results in no cone function due to a misfolding of transducin. Cone photoreceptors also show signs of opsin mislocalization, retinal remodeling and degeneration. This naturally occurring model shows all the hallmark signs of achromatopsia.
authors.affiliation: Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Jobling
authors.forename: Kirstan A
authors.initials: KA
authors.lastname: Vessey
authors.forename: Michelle
authors.initials: M
authors.lastname: Waugh
authors.forename: Samuel A
authors.initials: SA
authors.lastname: Mills
authors.forename: Erica L
authors.initials: EL
authors.lastname: Fletcher
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003117:Color Vision Defects / Q000235:genetics / Q000473:pathology*; D004195:Disease Models, Animal; D004596:Electroretinography; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D008807:Mice, Inbred BALB C; D020125:Mutation, Missense; D055355:Opsins / Q000378:metabolism; D010641:Phenotype; D016133:Polymerase Chain Reaction; D017510:Protein Folding; D012160:Retina / Q000378:metabolism / Q000473:pathology*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D013997:Time Factors; D015293:Transducin / Q000378:metabolism*
chemical_list: C515337:Gnat2 protein, mouse; D055355:Opsins; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin
keywords: Gnat2; achromatopsia; cone photoreceptors; degeneration; transducin