Myotube Formation is Delayed but not Prevented in MyoD-deficient Skeletal Muscle: Studies in Regenerating Whole Muscle Grafts of Adult Mice

Abstract

We compared the time course of myogenic events in vivo in regenerating whole muscle grafts in MyoD(-/-) and control BALB/c adult mice using immunohistochemistry and electron microscopy. Immunohistochemistry with antibodies to desmin and myosin revealed a striking delay by about 3 days in the formation of myotubes in MyoD(-/-) autografts compared with BALB/c mice. However, myotube formation was not prevented, and autografts in both strains appeared similar by 8 days. Electron microscopy confirmed myotube formation in 8- but not 5-day MyoD(-/-) grafts. This pattern was not influenced by cross-transplantation experiments between strains examined at 5 days. Antibodies to proliferating cell nuclear antigen demonstrated an elevated level of replication by MyoD(-/-) myoblasts in autografts, and replication was sustained for about 3 days compared with controls. These data indicate that the delay in the onset of differentiation and hence fusion is related to extended proliferation of the MyoD(-/-) myoblasts. Overall, although muscle regeneration was delayed it was not impaired in MyoD(-/-) mice in this model.

Increased survival of muscle stem cells lacking the MyoD gene after transplantation into regenerating skeletal muscle

“…The adult skeletal muscle in mice lacking MyoD (MyoD Ϫ/Ϫ ) displays a deficiency in regeneration and strongly supports the assertion that MyoD plays an essential role in regulating the satellite cell myogenic program (13). In addition, we and other groups have demonstrated that satellite cell-derived primary myoblasts isolated from adult MyoD Ϫ/Ϫ mice display an accelerated growth rate and delayed terminal differentiation (2,(14)(15)(16)(17)(18)(19). Therefore, MyoD Ϫ/Ϫ myoblasts have been suggested to display characteristics that are more primitive than wild-type myoblasts and may represent an intermediate stage between stem and myogenic precursor cells.…”

“…However, severe limitations exist, including immune rejection of allogenic donor cells, poor cellular survival, and limited spread of the injected cells, hindering practical application (8). Previously, Grounds and colleagues (16,17) performed transplantation experiments by using sliced and whole muscle derived from MyoD Ϫ/Ϫ mice, demonstrating increased migratory activity and delayed myotube formation of MyoD Ϫ/Ϫ myoblasts in the host muscle. In this study, we demonstrate that myoblasts derived from muscle satellite cells lacking the MyoD gene are a potentially useful source for repair of damaged muscle in DMD patients.…”

All muscle satellite cells are equal, but are some more equal than others?

“…The activity of MyoD can, however, be controlled by its post-translational modification, by its association with repressor proteins or by inhibiting its interaction with DNA (Berkes and Tapscott, 2005), all of which allow it to be expressed in proliferating myoblasts without necessarily causing immediate differentiation. MyoD can be downregulated in satellite cells after division, and cell pairs in which MyoD remains expressed in only one cell have been observed (Zammit et al, 2004); and low or absent MyoD is associated with enhanced proliferation and delayed or perturbed myogenic differentiation (Asakura et al, 2007;White et al, 2000;Yablonka-Reuveni et al, 1999). The model shown in Fig.…”

Abnormal expression of seven myogenesis-related genes in extraocular muscles of patients with concomitant strabismus

“…MYOD knockout mice are deficient in skeletal muscle regeneration (30)(31)(32). In activated skeletal satellite cells, differentiating signals upregulate MYOD and activate the transcription of MYOD target genes, result in myogenic differentiation (33).…”