title: Six1 and Six4 homeoproteins are required for Pax3 and Mrf expression during myogenesis in the mouse embryo.
abstract: In mammals, Six5, Six4 and Six1 genes are co-expressed during mouse myogenesis. Six4 and Six5 single knockout (KO) mice have no developmental defects, while Six1 KO mice die at birth and show multiple organ developmental defects. We have generated Six1Six4 double KO mice and show an aggravation of the phenotype previously reported for the single Six1 KO. Six1Six4 double KO mice are characterized by severe craniofacial and rib defects, and general muscle hypoplasia. At the limb bud level, Six1 and Six4 homeogenes control early steps of myogenic cell delamination and migration from the somite through the control of Pax3 gene expression. Impaired in their migratory pathway, cells of the somitic ventrolateral dermomyotome are rerouted, lose their identity and die by apoptosis. At the interlimb level, epaxial Met expression is abolished, while it is preserved in Pax3-deficient embryos. Within the myotome, absence of Six1 and Six4 impairs the expression of the myogenic regulatory factors myogenin and Myod1, and Mrf4 expression becomes undetectable. Myf5 expression is correctly initiated but becomes restricted to the caudal region of each somite. Early syndetomal expression of scleraxis is reduced in the Six1Six4 embryo, while the myotomal expression of Fgfr4 and Fgf8 but not Fgf4 and Fgf6 is maintained. These results highlight the different roles played by Six proteins during skeletal myogenesis.
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: Raphaelle
authors.initials: R
authors.lastname: Grifone
authors.forename: Josiane
authors.initials: J
authors.lastname: Demignon
authors.forename: Christophe
authors.initials: C
authors.lastname: Houbron
authors.forename: Evelyne
authors.initials: E
authors.lastname: Souil
authors.forename: Claire
authors.initials: C
authors.lastname: Niro
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Seller
authors.forename: Ghislaine
authors.initials: G
authors.lastname: Hamard
authors.forename: Pascal
authors.initials: P
authors.lastname: Maire
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001842:Bone and Bones / Q000002:abnormalities; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D024510:Muscle Development / Q000502:physiology*; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism; D009132:Muscles / Q000002:abnormalities / Q000196:embryology; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors / Q000235:genetics* / Q000378:metabolism; D018008:Myogenin; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D009124:Muscle Proteins; C497418:Myf5 protein, mouse; C503801:Myog protein, mouse; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; C490947:Six1 protein, mouse; C098490:Six4 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; C063403:myogenic factor 6; C068686:Pax3 protein, mouse