Mutant mice are smaller than their littermates and develop an unsteady gait about 3 weeks of age (average 3.5weeks of age +/-0.5, n=22). The mice fail to thrive and die between 4-8 weeks of age. Males and females are affected and do not live long enough to mate normally. Although the NMF249 mutation arose in an ENU mutagenized family, it is most likely a spontaneous mutation. The parents showed 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. In vitro fertilization was attempted using sperm from a six-week-old mutant, however the yield was not sufficient to maintain the colony, and ovarian transplants (OTs) are required to maintain a colony.
The mice have a distal neuropathy in motor neurons with retracting axons and poorly innervated or denervated neuromuscular junctions 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. No defects have been observed in the CNS.
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. Due to reproductive problems, the colony was outcrossed to CAST/Ei mice. It is maintained by several generations of backcross to C57BL/6 followed by an outcross to CAST/Ei to improve breeding efficiency.
|Allele Name||neuroscience mutagenesis facility, 249|
|Allele Synonym(s)||GarsP234KY; GarsP278KY; Nmf249|
|Gene Symbol and Name||Gars, glycyl-tRNA synthetase|
|Strain of Origin||C57BL/6J|
|General Note||Although this phenotypic mutation was identified in an ENU mutagenesis screen, it is probably of spontaneous origin.|
|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 at codon 278 to be replaced with a tyrosine and lysine residue 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.|