title: Intrinsic signals regulate the initial steps of myogenesis in vertebrates.
abstract: In vertebrates, despite the evidence that extrinsic factors induce myogenesis in naive mesoderm, other experiments argue that the initiation of the myogenic program may take place independent of these factors. To resolve this discrepancy, we have re-addressed this issue, using short-term in vivo microsurgery and culture experiments in chick. Our results show that the initial expression of the muscle-specific markers Myf5 and MyoD is regulated in a mesoderm-autonomous fashion. The reception of a Wnt signal is required for MyoD, but not Myf5 expression; however, we show that the source of the Wnt signal is intrinsic to the mesoderm. Gain- and loss-of-function experiments indicate that Wnt5b, which is expressed in the presomitic mesoderm, represents the MyoD-activating cue. Despite Wnt5b expression in the presomitic mesoderm, MyoD is not expressed in this tissue: our experiments demonstrate that this is due to a Bmp inhibitory signal that prevents the premature expression of MyoD before somites form. Our results indicate that myogenesis is a multistep process which is initiated prior to somite formation in a mesoderm-autonomous fashion; as somites form, influences from adjacent tissues are likely to be required for maintenance and patterning of early muscles.
authors.affiliation: Laboratoire de Génétique et de Physiologie du Développement, Developmental Biology Institute of Marseille, CNRS UMR 6545, University Aix-Marseille II, Campus de Luminy, case 907, 13288 Marseille Cedex 09, France.
authors.forename: Claudia
authors.initials: C
authors.lastname: Linker
authors.forename: Cynthia
authors.initials: C
authors.lastname: Lesbros
authors.forename: Michael R
authors.initials: MR
authors.lastname: Stark
authors.forename: Christophe
authors.initials: C
authors.lastname: Marcelle
mesh_terms: D000818:Animals; D002642:Chick Embryo; D051157:Frizzled Receptors; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D024510:Muscle Development / Q000502:physiology*; D017570:MyoD Protein / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051153:Wnt Proteins; D029961:Zebrafish Proteins
chemical_list: D051157:Frizzled Receptors; D017570:MyoD Protein; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051153:Wnt Proteins; D029961:Zebrafish Proteins