Marker-assisted introgression of the Compact mutant myostatin allele Mstn Cmpt-dl1Abc into a mouse line with extreme growth effects on body composition and muscularity

Myostatin is a negative regulator of muscle growth and mutations in its gene lead to muscular hypertrophy and reduced fat. In cattle, this is seen in 'double muscled' breeds. We have used marker-assisted introgression to introduce a murine myostatin mutation, Mstn(Cmpt-dllAbc) [Compact (C)], into an inbred line of mice (DUHi) that had been selected on body weight and had exceptional growth. Compared with homozygous wild-type mice, homozygous (C/C) mice of this line were similar to4-5% liahter, had similar to7-8% shorter tails, substantially increased muscle weights (e.g. quadriceps muscle in males was 59% heavier) and an increased 'dressing percentage' (similar to49% vs 39%), an indicator of overall muscularity. The weights of several organs (e.g. liver, kidney, heart and digestive tract) were significantly reduced, by 12-20%. Myostatin deficiency also resulted in drastic reductions of total body fat and of various fat depots, total body fat proportion falling from similar to17-5% in wild-type animals of both sexes to 9-5% and 11-6% in homozygous (C/C) females and males, respectively. Males with a deficiency in myostatin had higher gains in muscle traits than females. Additionally, there was a strong distortion of the segregation ratio on the DUHi background. Of 838 genotyped pups from inter se matings 29%, 63% and 8% were homozygous wild type (+/+), heterozygous (C/+) and homozygous (C/C), respectively, showing that Mstn(Cmpt-dllAbc) has lower fitness on this background. This line, when congenic, will be a useful resource in gene expression studies and for finding modifying genes.