Fiber Type Composition of the Sternomastoid and Diaphragm Muscles of Dystrophin‐Deficient mdx Mice

Abstract

The muscle fiber phenotype is mainly determined by motoneuron innervation and changes in neuromuscular interaction alter the muscle fiber type. In dystrophin-deficient mdx mice, changes in the molecular assembly of the neuromuscular junction and in nerve terminal sprouting occur in the sternomastoid (STN) muscle during early stages of the disease. In this study, we were interested to see whether early changes in neuromuscular assembly are correlated with alterations in fiber type in dystrophic STN at 2 months of age. A predominance of hybrid fast myofibers (about 52% type IIDB) was observed in control (C57Bl/10) STN. In mdx muscle, the lack of dystrophin did not change this profile (about 54% hybrid type IIDB). Pure fast type IID fibers predominated in normal and dystrophic diaphragm (DIA; about 39% in control and 30% in mdx muscle) and a population of slow Type I fibers was also present (about 10% in control and 13% in mdx muscle). In conclusion, early changes in neuromuscular assembly do not affect the fiber type composition of dystrophic STN. In contrast to the pure fast fibers of the more affected DIA, the hybrid phenotype of the STN may permit dynamic adaptations during progression of the disease. Anat Rec, 293:1722Rec, 293: -1728

Triadin/Junctin Double Null Mouse Reveals a Differential Role for Triadin and Junctin in Anchoring CASQ to the jSR and Regulating Ca2+ Homeostasis

“…Mouse EDL contains a majority of fast twitch type IIB fibers [41], [42]; the sternomastoid a majority of fast twitch type IIX fibers [43]. These two muscles are composed of fast twitch fibers that not only share equivalent structure but also displayed similar type and levels of structural alterations in all mutated mice.…”

Functional and histopathological identification of the respiratory failure in a DMSXL transgenic mouse model of Myotonic Dystrophy

“…In fact, the increase in histochemically defined type I muscle fibers, the presence of central nuclei, the gain in interfasicular connective tissue and inflammatory cells, as well as the accumulation of expanded CUG mRNA in muscle fiber nuclei all indicate that the diaphragm muscle of DMSXL mice is involved in the dystrophic processes. This assumption can be supported, on the one hand, by the presence of similar histopathological changes in biopsies of DM1 patients (Harper, 1989; Romeo, 2012) and, on the other hand, by the changes in fiber type composition of the diaphragm muscles in an animal model of Duchenne muscular dystrophy, which is characterized by severe muscle degeneration (Guido et al, 2010; Petrof et al, 1993). These authors hypothesize that the progressive changes in fiber type probably permit better adaptation of the muscle to its function during progression of the disease.…”

Muscle-Derived Extracellular Signal-Regulated Kinases 1 and 2 Are Required for the Maintenance of Adult Myofibers and Their Neuromuscular Junctions

“…We sought to determine the fiber type composition of the STN and TA in our Erk1/2 mutant mice. In the adult mouse, STN and TA are predominantly fast-fiber muscles (54)(55)(56). Our experiments confirmed these published observations, as our control and 3 mutant STN and TA muscles had a maximum of 0.2% type 1 fibers (data not shown).…”