title: Altered myogenesis in Six1-deficient mice.
abstract: Six homeoproteins are expressed in several tissues, including muscle, during vertebrate embryogenesis, suggesting that they may be involved in diverse differentiation processes. To determine the functions of the Six1 gene during myogenesis, we constructed Six1-deficient mice by replacing its first exon with the lacZ gene. Mice lacking Six1 die at birth because of severe rib malformations and show extensive muscle hypoplasia affecting most of the body muscles in particular certain hypaxial muscles. Six1(-/-) embryos have impaired primary myogenesis, characterized, at E13.5, by a severe reduction and disorganisation of primary myofibers in most body muscles. While Myf5, MyoD and myogenin are correctly expressed in the somitic compartment in early Six1(-/-) embryos, by E11.5 MyoD and myogenin gene activation is reduced and delayed in limb buds. However, this is not the consequence of a reduced ability of myogenic precursor cells to migrate into the limb buds or of an abnormal apoptosis of myoblasts lacking Six1. It appears therefore that Six1 plays a specific role in hypaxial muscle differentiation, distinct from those of other hypaxial determinants such as Pax3, cMet, Lbx1 or Mox2.
authors.affiliation: Département Génétique, Développement et Pathologie Moléculaire, Institut Cochin - INSERM 567, CNRS UMR 8104, Université Paris V, 24 Rue du Faubourg Saint Jacques, 75014 Paris, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Laclef
authors.forename: Ghislaine
authors.initials: G
authors.lastname: Hamard
authors.forename: Josiane
authors.initials: J
authors.lastname: Demignon
authors.forename: Evelyne
authors.initials: E
authors.lastname: Souil
authors.forename: Christophe
authors.initials: C
authors.lastname: Houbron
authors.forename: Pascal
authors.initials: P
authors.lastname: Maire
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D004622:Embryo, Mammalian / Q000033:anatomy & histology / Q000502:physiology; D005260:Female; D018390:Gene Targeting; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D024510:Muscle Development / Q000235:genetics / Q000502:physiology*; D018482:Muscle, Skeletal / Q000473:pathology / Q000502:physiology; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism; D018008:Myogenin / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D012272:Ribs / Q000473:pathology; D013249:Sternum / Q000473:pathology
chemical_list: D018398:Homeodomain Proteins; D017570:MyoD Protein; C503801:Myog protein, mouse; D018008:Myogenin; C490947:Six1 protein, mouse