Features of dystrophy in smooth and skeletal muscles of mdx mice

Gender dimorphism influences extracellular matrix expression and regeneration of muscular tissue in mdx dystrophic mice

Mdx mouse, the animal model of Duchenne muscular dystrophy, lacks dystrophin and develops an X-linked recessive inflammatory myopathy characterized by degeneration of skeletal muscle fibers and connective tissue replacement. The present work aimed to assess whether gender dimorphism in mdx mice would influence skeletal muscle pathology at ages corresponding to main histological changes in the microenvironment of muscular tissue: myonecrosis, regeneration, and fibrosis. At the height of myonecrosis (6 weeks postnatal), skeletal muscles of male mdx mice showed increased sarcolemmal permeability, numerous inflammatory foci, and marked deposition of the extracellular matrix components (ECM) type I collagen and laminin. In contrast, age-matched mdx females showed mild ECM deposition, discrete myonecrosis, but increased numbers of regenerating fibers expressing the satellite cell marker NCAM. In contrast ovariectomized mdx females showed decreased numbers of regenerating fibers. Older (24 and 48 weeks postnatal) mdx females showed extensive fibrosis with increased sarcolemmal permeability and marked deposition of ECM components than corresponding males. These results suggest a role for female hormones in the control of myonecrosis probably by promoting regeneration of muscular tissue and mitigating inflammation especially at ages under the critical influence of sex hormones.

Dmd(mdx-beta geo): a new allele for the mouse dystrophin gene

During a gene trap screen, an insertion of the gene trap vector into the dystrophin gene, creating a new allele for the Dmd gene, has been discovered. Because the ROSA beta geo vector was used, the new allele is called Dmd(mdx-beta geo). The insertion occurred 3' of exon 63 of the dystrophin gene, resulting in a mutation that affects all presently known dystrophin isoforms. In contrast to spontaneous or ENU-induced alleles, Dmd(mdx-beta geo) can be used to follow dystrophin expression by staining for beta-galactosidase activity. The high sensitivity of this method revealed additional and earlier expression of dystrophin during embryogenesis than that seen previously with other methods. Dystrophin promoters are active predominantly in the dermamyotome, limb buds, telencephalon, floor plate, eye, liver, pancreas anlagen, and cardiovascular system. Adult Dmd(mdx-beta geo) mice show reporter gene expression in brain, eye, liver, pancreas, and lung. In skeletal and heart muscle, beta-galactosidase activity is not detectable, confirming Western blot data that indicate the absence of the mutant full-length protein in these tissues. Hemizygous Dmd(mdx-beta geo) mice show muscular dystrophy with degenerating muscle fibers, cellular infiltration, and regenerated muscle fibers that have centrally located nuclei. Some mutant animals develop a dilated esophagus, probably due to constriction by the hypertrophic crura of the diaphragm.