title: Non conservation of function for the evolutionarily conserved prdm1 protein in the control of the slow twitch myogenic program in the mouse embryo.
abstract: Muscles are composed of multinucleated muscle fibers with different contractile and physiological properties, which result from specific slow or fast gene expression programs in the differentiated muscle cells. In the zebra fish embryo, the slow program is under the control of Hedgehog signaling from the notochord and floor plate. This pathway activates the expression of the conserved transcriptional repressor, Prdm1 (Blimp1), which in turn represses the fast program and promotes the slow program in adaxial cells of the somite and their descendants. In the mouse embryo, myogenesis is also initiated in the myotomal compartment of the somite, but the slow muscle program is not confined to a specific subset of cells. We now show that Prdm1 is expressed in the first differentiated myocytes of the early myotome from embryonic day (E)9.5-E11.5. During this period, muscle formation depends on the myogenic regulatory factors, Myf5 and Mrf4. In their absence, Prdm1 is not activated, in apparent contrast to zebra fish where Prdm1 is expressed in the absence of Myf5 and MyoD that drive myogenesis in adaxial cells. However, as in zebra fish, Prdm1 expression in the mouse myotome does not occur in the absence of Hedgehog signaling. Analysis of the muscle phenotype of Prdm1 mutant embryos shows that myogenesis appears to proceed normally. Notably, there is no requirement for Prdm1 activation of the slow muscle program in the mouse myotome. Furthermore, the gene for the transcriptional repressor, Sox6, which is repressed by Prdm1 to permit slow muscle differentiation in zebra fish, is not expressed in the mouse myotome. We propose that the lack of functional conservation for mouse Prdm1, that can nevertheless partially rescue the adaxial cells of zebra fish Prdm1 mutants, reflects differences in the evolution of the role of key regulators such as Prdm1 or Sox6, in initiating the onset of the slow muscle program, between teleosts and mammals.
authors.affiliation: Department of Developmental Biology, CNRS URA 2575, Institut Pasteur, Paris, France. stephane.vincent@igbmc.fr
authors.forename: Stéphane D
authors.initials: SD
authors.lastname: Vincent
authors.forename: Alicia
authors.initials: A
authors.lastname: Mayeuf
authors.forename: Claire
authors.initials: C
authors.lastname: Niro
authors.forename: Mitinori
authors.initials: M
authors.lastname: Saitou
authors.forename: Margaret
authors.initials: M
authors.lastname: Buckingham
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D017124:Conserved Sequence / Q000235:genetics*; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism*; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D005799:Genes, Dominant / Q000235:genetics; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D032342:Muscle Cells / Q000166:cytology / Q000378:metabolism; D024510:Muscle Development / Q000235:genetics*; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology / Q000378:metabolism*; D051787:Myogenic Regulatory Factor 5 / Q000235:genetics / Q000378:metabolism; D018006:Myogenic Regulatory Factors / Q000235:genetics / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D000074462:Positive Regulatory Domain I-Binding Factor 1; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D055755:SOXD Transcription Factors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015027:Zebrafish / Q000378:metabolism
chemical_list: D053823:Hedgehog Proteins; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; C513258:Prdm1 protein, mouse; D012333:RNA, Messenger; D055755:SOXD Transcription Factors; C465570:Shh protein, mouse; D014157:Transcription Factors; C063403:myogenic factor 6; D000074462:Positive Regulatory Domain I-Binding Factor 1; D018995:Myosin Heavy Chains