Detection of a point mutation (A to G) in exon 5 of the murine Mgf gene defines a novel allele at the Steel locus with a weak phenotype1

A new mutation at the locus encoding the mast cell growth factor (Mgf) is described and designated as Mgf^Sl-3Neu. Homozygous mutants have a light grey fur, sometimes with white patches. Homozygotes are fertile, but with reduced litter size, when mated inter se. Analysis of haematological parameters indicated no difference between mutant and wild-type mice. Sequence analysis of the cDNA obtained from the brain of homozygous mutants revealed an A→G exchange at position 400 leading to a predicted amino acid exchange from Asn→Leu at position 122. As a consequence of the predicted amino acid exchange an extension of the α-helical context and a decreased hydropathicity of the region at positions 101–125 can be deduced. This single amino acid exchange is outside of the known important domains of MGF and explains the weak phenotype of Mgf^Sl-3Neu.