B6;CAST-Gars1^Nmf249/RwbJ

Stock number: 033165
Product name: Gars^P278KY
Research areas: Developmental Biology Research, Mouse/Human Gene Homologs, Neurobiology Research

Description

B6;CAST-Gars1^Nmf249 heterozygous mice have a severe axonal neuropathy of both sensory and motor axons. Specifically, mice have abnormal neuromuscular junction morphology and impaired transmission, reduced nerve conduction velocities, and a loss of large-diameter peripheral axons without defects in myelination. These mice may be useful in studies of inherited Charcot-Marie-Tooth peripheral neuropathies, type 2D (CMT2D).

Detailed description

Gars1 (glycyl-tRNA synthetase 1 or GlyRS) encodes a tRNA synthetase that covalently links amino acids onto their cognate tRNAs. Mutations in GARS are associated with Charcot-Marie-Tooth neuropathies, type 2D (CMT2D). The spontaneous, dominant Gars1^Nmf249 allele has been identified as an amino acid substitution at codon 278 replacing proline with a tyrosine and lysine (P278KY) and is equivalent to the P234KY change in human GARS. The conserved proline is near the second catalytic domain. The substitution does not affect the open reading frame and appears to be a gain of function mutation. On the original C57BL/6J background, Nmf249 mice have a distal neuropathy in motor neurons with retracting axons (Figure 1) and poorly innervated or denervated neuromuscular junctions (Figure 2) visualized through immunohistochemistry of neuromuscular junctions; green labeling indicates the presence of neurofilament protein in axons (SMI31) and synaptic vesicle proteins at motor terminals (SV2); red labeling indicates ACh receptors visualized with rhodamine-labeled alpha-bungarotoxin; yellow color reveals the overlay of the presynaptic nerve with the motor terminal arborization). Large diameter myelinated fibers are absent and a significant number of unidentified cells is evident in the sciatic nerve of affected mice (Figure 3). No defects have been observed in the CNS. On the C57BL/6 background, heterozygous mice are smaller than their littermates and develop an unsteady gait about 3 weeks of age. The mice fail to thrive and die between 4-8 weeks of age. Homozygotes die before birth. Males and females are affected and do not live long enough to mate normally. Due to the difficulties in maintaining the strain, it is outcrossed to CAST/EiJ every few generations.

On the mixed B6;CAST background (this strain), heterozygotes exhibit decreased body weight and impaired mobility. After P7, axon number and diameter are reduced (with a minimal reduction in myelin thickness), neuromuscular junctions develop partial or complete denervation , femoral nerve size is reduced, and nerve conduction velocity is reduced by 25%. This strain may be useful for studying Charcot-Marie-Tooth disease type 2D.

Development

This phenotypic deviant was identified following multidose ethylnitrosourea (ENU) treatments to induce mutations in male founder C57BL/6J mice (Stock No. 000664), in the Neuroscience Mutagenesis Facility (NMF) at The Jackson Laboratory. The parents exhibited no overt phenotype and produced only 1 affected mouse in a total of 24 progeny. However, when this animal was mated to a wild-type male (using ovarian transplants), half the offspring was affected, suggesting that a spontaneous dominant mutation may have occurred. Ratios from subsequent matings are consistent with a fully penetrant dominant mutation. Sequence analysis indicates that the mutation is a nucleotide substitution resulting in the replacement of proline at codon 278 with a tyrosine and lysine in exon 7 of the glycyl-tRNA synthetase 1 (Gars1) gene. This highly conserved proline residue is near the second catalytic domain. Due to reproductive problems, the colony is outcrossed to CAST/EiJ (Stock No. 00928) mice and is maintained by several generations of backcross to C57BL/6 followed by an outcross to CAST/EiJ to improve breeding efficiency.  By crossing to CAST/EiJ, life expectancy is increased to approximately one year. The colony was maintained in the laboratory of Dr. Robert Burgess at The Jackson Laboratory, it was transferred to The Jackson Laboratory Repository in 2019.

Allele

Symbol: Gars1^Nmf249
Name: neuroscience mutagenesis facility, 249
MGI accession ID: MGI:3513831
Generation method: Spontaneous
Attributes: Not Applicable
Synonyms: Gars^P234KY; Gars^P278KY; Nmf249
Marker symbol: Gars1
Marker name: glycyl-tRNA synthetase 1
Marker synonyms: CMT2D; DSMAV; GARS; Gena201; GENA202; GlyRS; HMN5; HMN5A; HMND5; RGD1559871; Sgrp23; SMAD1; SMAJI
Chromosome: 6
Strain of origin: C57BL/6J
Molecular note: Sequence analysis revealed that a CC pair in the open reading frame was changed to AAATA. This nucleotide substitution results in the proline codon 278 (CCT) to be replaced with tyrosine and lysine codons (AAATAT) (p.P234delinsKY) without affecting the rest of the open reading frame. This highly conserved proline residue is near the second catalytic domain. Expression of transcript from this allele does not appear to be affected by this mutation. It is predicted to be a gain-of-function mutation.
General note: Although this phenotypic mutation was identified in an ENU mutagenesis screen, it is probably of spontaneous origin.