MAP kinase converts MyoD into an instructive muscle differentiation factor in Xenopus.
In amphibian development, muscle is specified in the dorsal lateral marginal zone (DLMZ) of the gastrula embryo. Two critical events specify the formation of skeletal muscle: the expression of the myogenic transcription factor, XMyoD, and the secretion of bone morphogenetic protein (BMP) antagonists by the adjacent Spemann organizer. Inhibition of BMP signaling during early gastrula stages converts XMyoD protein into an instructive differentiation factor in the DLMZ. Yet, the intracellular signaling factors connecting BMP antagonism and activation of XMyoD remain unknown. Our data show that BMP antagonism induces the activity of mitogen-activated protein kinase (MAPK), and that the activity of MAPK is necessary for muscle-specific differentiation. Treatment of gastrula-stage DLMZ explants with MAPK pathway inhibitors ventralized mesoderm and prevented muscle differentiation. Expression of XMyoD in ventral mesoderm weakly induced muscle formation; however, the coexpression of a constitutively active MEK1 with XMyoD efficiently induced muscle differentiation. Activation of the MAPK pathway did not induce the transcription of XMyoD, but increased its protein levels and transcriptional activity. Thus, MAPK activation is subsequent to BMP antagonism, and participates in the dorsalization of mesoderm by converting the XMyoD protein into a potent differentiation factor.
Zetser
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A
Department of Biochemistry, The Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, 31096, Israel.
Frank
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D
Bengal
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E
D000818:Animals; D015153:Blotting, Western; D019521:Body Patterning; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D004789:Enzyme Activation; D008648:Mesoderm; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000196:embryology* / Q000201:enzymology / Q000378:metabolism; D017570:MyoD Protein / Q000378:metabolism*; D010766:Phosphorylation; D015398:Signal Transduction; D014981:Xenopus / Q000196:embryology
D019485:Bone Morphogenetic Proteins; D017570:MyoD Protein; D020928:Mitogen-Activated Protein Kinases