PERSISTENT EXPRESSION OF MNF IDENTIFIES MYOGENIC STEM-CELLS IN POSTNATAL MUSCLES

Skeletal muscles contain an undifferentiated myogenic stem cell pool ( satellite cells) that can be mobilized to regenerate myofibers in resp onse to injury. We have determined that the winged helix transcription factor MNF is expressed selectively in quiescent satellite cells, whi ch do not express known regulators of the myogenic program. Following muscle injury, MNF is present transiently in proliferating satellite c ells and in centralized nuclei of regenerating myofibers, but expressi on declines as these fibers mature, until only the residual stem cell pool continues to express detectable levels of MNF. MNF also is expres sed selectively but transiently at embryonic stages of myogenesis in t he developing myotome, limb bud precursors, and heart tube, but by lat e fetal stages of development, MNF is down-regulated within differenti ated cardiac and skeletal myocytes, and persistently high expression i s observed only in satellite cells. These data identify MNF as a marke r of quiescent satellite cells and suggest that downstream genes contr olled by MNF serve to modulate proliferative growth or differentiation in this unique cell population. (C) 1997 Academic Press.