A unique pattern of expression of the four muscle regulatory factor proteins distinguishes somitic from embryonic, fetal and newborn mouse myogenic cells.
A unique pattern of expression of the four muscle regulatory factor (MRF) proteins was found to distinguish early somitic from embryonic, fetal and newborn limb myogenic cells in vitro. Expression of the myosin heavy chain (MHC), MyoD, myogenin, Myf-5, and MRF4 proteins was examined by immunocytochemistry in cultures of four distinct types of mouse myogenic cells: somitic (E8.5), embryonic (E11.5), fetal (E16.5) and newborn limb. In embryonic, fetal and newborn cultures, the MRF proteins were expressed in generally similar patterns: MyoD was the first MRF expressed; MyoD and myogenin were expressed by more cells than Myf-5 or MRF4; and each of the four MRFs was found both in cells that expressed MHC and in cells that did not express MHC. In cultures of somitic cells, in contrast, Myf-5 was expressed first and by more cells than MyoD or myogenin; MRF4 was not detected; and the MRFs were never found to be coexpressed with MHC in the same cell. Thus, some somitic cells had the unexpected ability to maintain MHC expression in the absence of detectable MRF protein expression. The different myogenic programs of embryonic, fetal and newborn myogenic cells are not, therefore, a simple result of qualitatively different MRF expression patterns, whereas myogenesis by somitic cells does include a unique pattern of MRF expression.
Neuromuscular Laboratory, Massachusetts General Hospital, Charlestown 02129.
T H
TH
Smith
N E
NE
Block
S J
SJ
Rhodes
S F
SF
Konieczny
J B
JB
Miller
D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D015870:Gene Expression / Q000502:physiology; D007150:Immunohistochemistry; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics*; D009132:Muscles / Q000166:cytology / Q000196:embryology*; D017570:MyoD Protein; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D015534:Trans-Activators
D004268:DNA-Binding Proteins; D009124:Muscle Proteins; C497418:Myf5 protein, mouse; D017570:MyoD Protein; C503801:Myog protein, mouse; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D015534:Trans-Activators; C063403:myogenic factor 6