A Novel Intronic Single Nucleotide Polymorphism in the Myosin heavy polypeptide 4 Gene Is Responsible for the Mini-Muscle Phenotype Characterized by Major Reduction in Hind-Limb Muscle Mass in Mice

Abstract

Replicated artificial selection for high levels of voluntary wheel running in an outbred strain of mice favored an autosomal recessive allele whose primary phenotypic effect is a 50% reduction in hind-limb muscle mass. Within the High Runner (HR) lines of mice, the numerous pleiotropic effects (e.g., larger hearts, reduced total body mass and fat mass, longer hind-limb bones) of this hypothesized adaptive allele include functional characteristics that facilitate high levels of voluntary wheel running (e.g., doubling of mass-specific muscle aerobic capacity, increased fatigue resistance of isolated muscles, longer hind-limb bones). Previously, we created a backcross population suitable for mapping the responsible locus. We phenotypically characterized the population and mapped the Minimsc locus to a 2.6-Mb interval on MMU11, a region containing 100 known or predicted genes. Here, we present a novel strategy to identify the genetic variant causing the mini-muscle phenotype. Using high-density genotyping and whole-genome sequencing of key backcross individuals and HR mice with and without the mini-muscle mutation, from both recent and historical generations of the HR lines, we show that a SNP representing a C-to-T transition located in a 709-bp intron between exons 11 and 12 of the Myosin heavy polypeptide 4 (Myh4) skeletal muscle gene (position 67,244,850 on MMU11; assembly, December 2011, GRCm38/mm10; ENSMUSG00000057003) is responsible for the mini-muscle phenotype, Myh4 Minimsc . Using next-generation sequencing, our approach can be extended to identify causative mutations arising in mouse inbred lines and thus offers a great avenue to overcome one of the most challenging steps in quantitative genetics.

Maternal exposure to Western diet affects adult body composition and voluntary wheel running in a genotype-specific manner in mice

“…Posterior subcutaneous fat pad, abdominal pelvic fat pad, liver, spleen, and brain masses were unaffected by maternal WD (Table 1). As reported previously [53], HR mice tended to have larger brains than C mice. Mice with the mini-muscle phenotype had larger hearts, livers, spleens, and both fat pads (Table 1), with several of these effects being reported previously (see Discussion).…”

Effects of selective breeding for high voluntary wheel‐running behavior on femoral nutrient canal size and abundance in house mice

“…Two of the HR lines and one of the C lines were observed to have individuals with hindlimb muscles that were reduced by~50% as compared with normal-muscle individuals Houle-Leroy et al 2003). This 'mini-muscle' phenotype is caused by an autosomal, Mendelian-recessive, single nucleotide polymorphism (Kelly et al 2013). The mini-muscle phenotype was originally present at low frequency in the base population and has increased in frequency in subsequent generations in both HR lines , resulting in fixation in HR line 3 and~50% frequency in HR line 6 (Syme et al 2005).…”

Hormones and the Evolution of Complex Traits: Insights from Artificial Selection on Behavior

“…As of the current generation (76), various aspects of exercise physiology and morphology have changed in the HR lines, including increases in endurance capacity (Meek et al 2009), maximal oxygen consumption Kolb et al 2010), heart size (Kolb et al 2010), size of femoral head and hindlimb symmetry (Garland and Freeman 2005), along with reductions in muscle mass Kelly et al 2013) and alterations in muscle fiber type (Bilodeau et al 2009). In addition to an increased ability for aerobically supported exercise, mice from the HR lines have alterations in the brain reward system that presumably indicate higher motivation for wheel running Belke and Garland 2007;Rhodes and Kawecki 2009;Keeney et al 2012).…”