STOCK Gnat2^cpfl3 Gnat1^irdr/BocJ

Stock number: 033163
Strain synonyms: B6.Cg-Gnat2^cpfl3 Gnat1^irdr/BocJ
Research areas: Sensorineural Research

Description

This congenic strain has spontaneous mutations in both the rod and cone forms of the alpha subunit of the heterotrimeric G protein transducin, impacting both rod and cone responses and resulting in congenital blindness.

Detailed description

On this C57BL/6J congenic genetic background the combined spontaneous mutations in Gnat2 and Gnat1 cause congenital blindness. There are no detectible rod or cone responses in either dark-adapted or light-adapted electroretinograms as early as 3 weeks of age, the earliest timepoint assessed. Fundus photographs are normal and no abnormalities are detected in retinal structure by 6 months of age by OCT (Optical coherence tomography) and histology.

Development

Dr. Bo Chang found that both the Gnat2^cpfl3 and Gnat1^irdr alleles were in STOCK Tg(tetO-HIST1H2BJ/GFP)47Efu/J (Stock# 005104), which derived from CD1. Non-transgenic mice from this line that were carrying the Gnat2^cpfl3 and Gnat1^irdr alleles were sibling intercrossed for several generations and then the Gnat1^irdr mutation was bred away from Gnat2^cpfl3 by backcrossing to C57BL/6J to generate the congenic strain B6.Cg-Gnat1^irdr/Boc (Stock# 008811) which was then sibling inbred to homozygosity for Gnat1^irdr. The double mutant strain ceased breeding, so to replace that strain Dr. Chang crossed B6.Cg-Gnat1^irdr/Boc with B6.Cg-Gnat2^cpfl3/Boc (Stock# 006795), a congenic strain that had been generated by backcrossing Gnat2^cpfl3 from ALS/LtJ onto C57BL/6J. The resulting double mutant on a C57BL/6J congenic background was sibling intercrossed to homozygosity and maintained by intercrossing double homozygotes, with this strain reaching N5F7 in early 2019. It was frozen as homozygous sperm by the donating investigator in 2022. See SNP results below.

Gnat2 mutation: A single nucleotide substitution of G to A at coding nucleotide 598 in exon 6. This mutation converts codon 200 from aspartic acid to asparagine (p.D200N).

Gnat1 mutation: The molecular mutation is a 57 bp deletion in intron 4 of the gene, which alters the splice donor site. This results in retention of the remaining 48 bp of the intron in the expressed mRNA. The insertion converts a cytosine to a guanine at nucleotide position 450 of the ORF and changes codon 150 (TAC) to a stop codon (TAG) (amino acid change: Tyr150Ter). Western blot analysis showed that no detectable protein is expressed from this allele. Because this mutation was found in ICR and CD1 it is carried in many strains, including IRD1 and IRD2.

In 2024, a 48 SNP (single nucleotide polymorphism) panel analysis, with 43 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the first generation of cryo recovered mice [the 2022 frozen sperm used to fertilize C57BL/6J oocytes] at The Jackson Laboratory Repository. Three of the 43 markers throughout the genome were segregating, suggesting the 2022 frozen sperm provided to The Jackson Laboratory Repository were on a mixed genetic background. Some of the recovered double mutant males will be used to replace the frozen sperm public bankstock in 2024.

Allele

Symbol: Gnat2^cpfl3
Name: cone photoreceptor function loss 3
MGI accession ID: MGI:3588845
Generation method: Spontaneous
Synonyms: no cones
Marker symbol: Gnat2
Marker name: guanine nucleotide binding protein, alpha transducing 2
Marker synonyms: ACHM4; Gnat-2; GNATC; Gt-2; HG1D; Tcalpha
Chromosome: 3
Strain of origin: various
Molecular note: A single nucleotide substitution of G to A at coding nucleotide 598 in exon 6. This mutation converts codon 200 from aspartic acid to asparagine (p.D200N).
General note: This allele has been detected in the following strains either by genotyping or complementation testing: ALS/LtJ, SENCARA/PtJ, SENCARB/PtJ, SENCARC/PtJ, PN/nBSwUmabJ. (J:122428) The allele has also been reported in NMRI and CD1 (Lluis Montoliu, J:212307)

Allele

Symbol: Gnat1^irdr
Name: ICR derived retinal dysfunction rod
MGI accession ID: MGI:3707708
Generation method: Spontaneous
Synonyms: rd17; retinal degeneration 17
Marker symbol: Gnat1
Marker name: guanine nucleotide binding protein, alpha transducing 1
Marker synonyms: CSNB1G; CSNBAD3; GBT1; Gnat-1; GNATR; HG1F; Ird1; Ird2; irdr; Tralpha; transducin
Chromosome: 9
Strain of origin: ICR
Molecular note: The molecular mutation is a 57 bp deletion in intron 4 of the gene, which alters the splice donor site. This results in retention of the remaining 48 bp of the intron in the expressed mRNA. The insertion converts a cytosine to a guanine at nucleotide position 450 of the ORF and changes codon 150 (TAC) to a stop codon (TAG) (amino acid change: Tyr150Ter). Western blot analysis showed that no detectable protein is expressed from this allele. Because this mutation was found in ICR and CD1 it is carried in many strains, including IRD1 and IRD2.
General note: Mice homozygous for this mutation have impaired rod electrophysiology but normal retinal morphology.