Dedifferentiation of Mammalian Myotubes Induced by msx1

Abstract

The process of cellular differentiation culminating in terminally differentiated mammalian cells is thought to be irreversible. Here, we present evidence that terminally differentiated murine myotubes can be induced to dedifferentiate. Ectopic expression of msx1 in C2C12 myotubes reduced the nuclear muscle proteins MyoD, myogenin, MRF4, and p21 to undetectable levels in 20%-50% of the myotubes. Approximately 9% of the myotubes cleave to produce either smaller multinucleated myotubes or proliferating, mononucleated cells. Finally, clonal populations of the myotube-derived mononucleated cells can be induced to redifferentiate into cells expressing chondrogenic, adipogenic, myogenic, and osteogenic markers. These results suggest that terminally differentiated mammalian myotubes can dedifferentiate when stimulated with the appropriate signals and that msx1 can contribute to the dedifferentiation process.

The molecular basis of amphibian limb regeneration: integrating the old with the new

“…Although the newt cells arrest in the cell cycle, the c2c12-derived mononucleate cells are proliferative and recapitulate the developmental potential of the parent cell line. 41 The ability of Msx-1 to induce this response in vitro is consistent with other lines of evidence indicating that Msx transcription factors are important for regeneration in vivo in amphibians as well as in mammals. 16,[43][44][45][46][47] An extract of regenerating limb blastemas also induces formation of proliferative mononucleate cells from c2c12 myotubes in vitro, 48 indicating the presence of blastema factor(s) involved in the control of the differentiated state in a multipotent mesenchymal stem cell population.…”

“…Of particular significance to regeneration is the observation that when Msx-1 is expressed in c2c12 myotubes, these multinucleate cells fragment to give rise to mononucleate cells. 41 A similar response is observed when myotubes derived from an urodele (newt) cell line is exposed to serum, 42 and both are being investigated as model systems for muscle 'dedifferentiation' and regeneration. Although the newt cells arrest in the cell cycle, the c2c12-derived mononucleate cells are proliferative and recapitulate the developmental potential of the parent cell line.…”

“…16,[43][44][45][46][47] An extract of regenerating limb blastemas also induces formation of proliferative mononucleate cells from c2c12 myotubes in vitro, 48 indicating the presence of blastema factor(s) involved in the control of the differentiated state in a multipotent mesenchymal stem cell population. Given that Msx-1 is known to be causally linked to fragmentation, 41 this may indicate that there are factors in blastemas that regulate Msx expression. Several signaling molecules are known to have this ability, including members of the FGF, Wnt, and BMP signaling pathways, 32,[49][50][51][52][53][54] which are obvious candidates for further studies.…”

Beyond early development: Xenopus as an emerging model for the study of regenerative mechanisms

“…Both, genes associated with Notch signalling and Msx genes were expressed similarly during development and regeneration of the tail . Msx1 and 2 are transcriptional repressors known to function downstream of Bmp signalling (Suzuki et al, 1997) and are associated with dedifferentiation of muscle cells in urodele appendage regeneration (Odelberg et al, 2000). Other genes known to be involved in development, such as posterior Hox genes, are also re-expressed during tail regeneration , and fibroblast growth factor-2 (fgf-2 or b-fgf) is up-regulated in the spinal cord after amputation (Zhang et al, 2000).…”

“…The transcription factor Msx-1, a direct downstream target of Bmp signalling, has been implicated in regeneration of various appendages and tissues (Odelberg et al, 2000;Kumar et al, 2004). Expression of a hyperactive version of HS-Msx-1 transgene in tails cut during the refractory period was also able to restore regeneration.…”