MyoD protein accumulates in satellite cells and is neurally regulated in regenerating myotubes and skeletal muscle fibers

Abstract

MyoD belongs to a family of helix-loop-helix proteins that control myogenic differentiation. Transfection of various non-myogenic cell lines with MyoD transforms them into myogenic cells. In normal embryonic development MyoD is upregulated at the time when the hypaxial musculature begins to form, but its role in the function of adult muscle remains to be elucidated. In this study we examined the cellular locations of MyoD protein in normal and abnormal muscles to see whether the presence of MyoD protein is correlated with a particular cellular behaviour and to assess the usefulness of MyoD as a marker for satellite cells. Adult rats were anaesthetised and their tibialis anterior or soleus muscles either denervated, tenotomised, freeze lesioned, lesioned and denervated, or lesioned and tenotomised. At various intervals after the operations the rats were killed and their muscles removed, snap frozen, and sectioned with a cryostat along with muscles from unoperated neonatal and adult rats. The sections were processed for immunohistochemistry using a rabbit affinity-purified antibody to recombinant MyoD. MyoD proved to be an excellent marker for active satellite cells; satellite cells in neohatal and regenerating muscles contained high levels of MyoD protein. MyoD positive cells were not observed in the muscles of old adults, in which the satellite cells are fully quiescent. MyoD immunoreactivity was rapidly lost from satellite cell nuclei after they fused into myotubes and was not detected in either sub-synaptic or non-synaptic nuclei of mature fibers. Denervation, and to a lesser extent tenotomy, of lesioned muscles induced expression of MyoD in myotubal nuclei. Denervation of normal muscles also upregulated MyoD in muscle fiber nuclei, an effect which was maximal after 3 days. We conclude that MyoD protein is neurally regulated in both myotubes and muscle fibers.

Highly Coordinated Gene Regulation in Mouse Skeletal Muscle Regeneration

“…Here we performed indirect immunofluorescence for detection of BrdUrd incorporation to mark proliferative cells on control and injured (day 3) muscle sections. We also stained the same sections for MyoD, Mac-1, or ag 7/4 as markers for proliferating myoblasts (34,35), peripheral macrophages (36), and infiltrating neutrophils (37), respectively. We predicted that a great portion of MyoD-positive cells would be positive for BrdUrd staining, and none of the Mac-1 or ag 7/4-positive cells would be positive for BrdUrd because cycling myoblasts expresses MyoD prior to terminal differentiation, whereas peripheral functional macrophages and neutrophils are terminally differentiated.…”

In Vivo Activation of STAT3 Signaling in Satellite Cells and Myofibers in Regenerating Rat Skeletal Muscles

“…MyoD plays critical roles in development and regeneration of skeletal muscles, and rapid upregulation of MyoD mRNA and protein after muscle injury is detected in nuclei of all myogenic cells and myonuclei (Fuchtbauer and Westphal 1992;Grounds et al 1992;Koishi et al 1995;Cooper et al 1999). In the present study, significant MyoD immunoreactivity was not detected in intact and 3-hr post-injured muscles (data not shown), but intense MyoD staining was observed in injured muscles at day 1 after injury ( Figure 3A).…”

Heart regeneration in adult MRL mice

“…The general mechanism of wound healing usually studied in adult mammals is repair, in contrast to the regeneration seen in more primitive vertebrates (1)(2)(3). There are, however, mammalian tissues that can regenerate, such as adult mammalian skeletal muscle, which recruits a population of mitotically active satellite cells that contribute to the resultant stable population of myonuclei (4). By contrast, amphibian skeletal muscle myonuclei undergo division concurrent with satellite cell activation and proliferation (5)(6)(7).…”