title: Six proteins regulate the activation of Myf5 expression in embryonic mouse limbs.
abstract: Myf5, a member of the myogenic regulatory factor family, plays a major role in determining myogenic cell fate at the onset of skeletal muscle formation in the embryo. Spatiotemporal control of its expression during development requires multiple enhancer elements spread over >100 kb at the Myf5 locus. Transcription in embryonic limbs is regulated by a 145-bp element located at -57.5 kb from the Myf5 gene. In the present study we show that Myf5 expression is severely impaired in the limb buds of Six1(-/-) and Six1(-/-)Six4(-/+) mouse mutants despite the presence of myogenic progenitor cells. The 145-bp regulatory element contains a sequence that binds Six1 and Six4 in electromobility shift assays in vitro and in chromatin immunoprecipitation assays with embryonic extracts. We further show that Six1 is able to transactivate a reporter gene under the control of this sequence. In vivo functionality of the Six binding site is demonstrated by transgenic analysis. Mutation of this site impairs reporter gene expression in the limbs and in mature somites where the 145-bp regulatory element is also active. Six1/4 therefore regulate Myf5 transcription, together with Pax3, which was previously shown to be required for the activity of the 145-bp element. Six homeoproteins, which also directly regulate the myogenic differentiation gene Myogenin and lie genetically upstream of Pax3, thus control hypaxial myogenesis at multiple levels.
authors.affiliation: Département de Génétique et Développement, Institut Cochin, Université Paris Descartes, Paris, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Giordani
authors.forename: Lola
authors.initials: L
authors.lastname: Bajard
authors.forename: Josiane
authors.initials: J
authors.lastname: Demignon
authors.forename: Philippe
authors.initials: P
authors.lastname: Daubas
authors.forename: Margaret
authors.initials: M
authors.lastname: Buckingham
authors.forename: Pascal
authors.initials: P
authors.lastname: Maire
mesh_terms: D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D002642:Chick Embryo; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D018878:Limb Buds; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D051787:Myogenic Regulatory Factor 5 / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors / Q000502:physiology; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
chemical_list: D018398:Homeodomain Proteins; C497418:Myf5 protein, mouse; D051787:Myogenic Regulatory Factor 5; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; C490947:Six1 protein, mouse; C098490:Six4 protein, mouse; D015534:Trans-Activators; C068686:Pax3 protein, mouse