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Molecular cloning of up-regulated cytoskeletal genes from regenerating skeletal muscle: potential role of myocyte enhancer factor 2 proteins in the activation of muscle-regeneration-associated genes.

ABSTRACT: A subtractive hybridization and cloning strategy was used to identify genes that are up-regulated in regenerating compared with normal skeletal muscle. The gastrocnemius muscle of CD1 mice was injected with a myotoxic agent (BaCl2). A cDNA library was constructed from the regenerating muscle, and was screened with subtracted probes enriched in genes up-regulated during regeneration. Cofilin and vimentin cDNA clones were isolated. Both cofilin and vimentin were demonstrated to be overexpressed in regenerating compared with non-regenerating muscle (17-fold and 19-fold induction respectively). Cofilin and vimentin mRNAs also exhibited an increased expression in C2C12 myoblasts and a decreased expression in differentiated myotubes. Analysis of the regeneration-induced vimentin enhancer/promoter region revealed a consensus binding site for the myocyte enhancer factor 2 (MEF2) transcription factors. Electrophoretic mobility-shift assays and in vivo reporter assays revealed that MEF2 DNA-binding activity and transcriptional activation are increased in regenerating skeletal muscle, indicating that they may play a role in the activation of muscle genes during regeneration. These data suggest that both cofilin (an actin-regulatory protein) and vimentin (an intermediate filament) may be key components of the cytoskeletal reorganization that mediates muscle cell development and adult skeletal-muscle repair.

SUBMITTER: Akkila WM

PROVIDER: S-EPMC1218532 | biostudies-other | 1997 Jul

REPOSITORIES: biostudies-other

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Project description:PurposeThe purpose of this study was to characterize the injury response of extraocular muscles (EOMs) in adult zebrafish.MethodsAdult zebrafish underwent lateral rectus (LR) muscle myectomy surgery to remove 50% of the muscle, followed by molecular and cellular characterization of the tissue response to the injury.ResultsFollowing myectomy, the LR muscle regenerated an anatomically correct and functional muscle within 7 to 10 days post injury (DPI). Following injury, the residual muscle stump was replaced by a mesenchymal cell population that lost cell polarity and expressed mesenchymal markers. Next, a robust proliferative burst repopulated the area of the regenerating muscle. Regenerating cells expressed myod, identifying them as myoblasts. However, both immunofluorescence and electron microscopy failed to identify classic Pax7-positive satellite cells in control or injured EOMs. Instead, some proliferating nuclei were noted to express mef2c at the very earliest point in the proliferative burst, suggesting myonuclear reprogramming and dedifferentiation. Bromodeoxyuridine (BrdU) labeling of regenerating cells followed by a second myectomy without repeat labeling resulted in a twice-regenerated muscle broadly populated by BrdU-labeled nuclei with minimal apparent dilution of the BrdU signal. A double-pulse experiment using BrdU and 5-ethynyl-2'-deoxyuridine (EdU) identified double-labeled nuclei, confirming the shared progenitor lineage. Rapid regeneration occurred despite a cell cycle length of 19.1 hours, whereas 72% of the regenerating muscle nuclei entered the cell cycle by 48 hours post injury (HPI). Dextran lineage tracing revealed that residual myocytes were responsible for muscle regeneration.ConclusionsEOM regeneration in adult zebrafish occurs by dedifferentiation of residual myocytes involving a muscle-to-mesenchyme transition. A mechanistic understanding of myocyte reprogramming may facilitate novel approaches to the development of molecular tools for targeted therapeutic regeneration in skeletal muscle disorders and beyond.

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Molecular cloning of up-regulated cytoskeletal genes from regenerating skeletal muscle: potential role of myocyte enhancer factor 2 proteins in the activation of muscle-regeneration-associated genes.

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