Effects of the muscular dysgenesis gene on developmental stability in the mouse mandible

Muscular dysgenesis (mdg) is an autosomal recessive gene in mice affecting primarily the skeletal musculature. mdg/mdg mice exhibit developmental arrest of myogenesis and degenerative changes in all skeletal muscles. In addition, there are pronounced abnormalities in skeletal traits, including the shape of the skull and mandible. Herein, we examine the phenotypic consequences of a single mdg allele in the heterozygous condition (+/mdg) on the size, shape, and developmental stability in 14 osteometric traits from the mouse mandible. Developmental stability in the mandible is measured by fluctuating asymmetry in bilateral traits. There are no statistically significant differences in the size or shape of the mandible between +/+ and +/mdg mice. However, compared to +/+ mice, +/mdg individuals exhibit less developmental stability for several mandible traits. The more unstable traits include height at the mandibular notch, height at the incisive process, condyloid width, height and area of the coronoid process, and size of the tooth-bearing region. All of these latter traits are closely associated with areas of muscle attachment and/or the muscular dysgenesis phenotype, suggesting that the presence of a single mdg allele is sufficient to alter developmental pathways. Traits not showing significantly increased instability in +/mdg mice bear no clear relationship to either muscle attachment areas or to the mdg/mdg phenotype.