title: Expansion of revertant fibers in dystrophic mdx muscles reflects activity of muscle precursor cells and serves as an index of muscle regeneration.
abstract: Duchenne muscular dystrophy and the mdx mouse myopathies reflect a lack of dystrophin in muscles. However, both contain sporadic clusters of revertant fibers (RFs) that express dystrophin. RF clusters expand in size with age in mdx mice. To test the hypothesis that the expansion of clusters is achieved through the process of muscle degeneration and regeneration, we analyzed muscles of mdx mice in which degeneration and regeneration were inhibited by the expression of micro-dystrophins or utrophin transgenes. Postnatal RF expansion was diminished in direct correlation to the protective effect of the transgene expression. Similarly, expansion of RFs was inhibited when muscle regeneration was blocked by irradiation. However, in irradiated muscles, irradiation-tolerant quiescent muscle precursor cells reactivated by notexin effectively restored RF expansion. Our observations demonstrate that revertant events occur initially within a subset of muscle precursor cells. The proliferation of these cells, as part of the regeneration process, leads to the expansion of RF clusters within degenerating muscles. This expansion of revertant clusters depicts the cumulative history of regeneration, thus providing a useful index for functional evaluation of therapies that counteract muscle degeneration.
authors.affiliation: Muscle Cell Biology Group, Medical Research Council Clinical Science Centre, Hammersmith Hospital Campus, Imperial College School of Medicine, London University, Du Cane Road, London, W12 0NN, UK.
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Yokota
authors.forename: Qi-Long
authors.initials: QL
authors.lastname: Lu
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Morgan
authors.forename: Kay E
authors.initials: KE
authors.lastname: Davies
authors.forename: Rosie
authors.initials: R
authors.lastname: Fisher
authors.forename: Shin'ichi
authors.initials: S
authors.lastname: Takeda
authors.forename: Terence A
authors.initials: TA
authors.lastname: Partridge
mesh_terms: D000818:Animals; D016189:Dystrophin / Q000502:physiology; D004546:Elapid Venoms / Q000627:therapeutic use; D051379:Mice; D008810:Mice, Inbred C57BL; D018101:Mice, Inbred mdx; D008822:Mice, Transgenic; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000528:radiation effects; D009132:Muscles / Q000502:physiology* / Q000528:radiation effects; D020388:Muscular Dystrophy, Duchenne / Q000188:drug therapy; D032446:Myoblasts / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D012038:Regeneration / Q000528:radiation effects; D012508:Sarcolemma / Q000201:enzymology; D049411:Utrophin / Q000502:physiology; D014916:Whole-Body Irradiation
chemical_list: D016189:Dystrophin; D004546:Elapid Venoms; D049411:Utrophin; C005082:notexin; D019001:Nitric Oxide Synthase