title: The role of the notochord for epaxial myotome formation in the mouse.
abstract: The vertebrate somite is the source of all trunk skeletal muscles. Myogenesis in avian embryos is thought to depend on signals from notochord and neural tube for the epaxial muscles, and signals from lateral mesoderm and surface ectoderm for the hypaxial muscles. However, this hypothesis has to be tested because in mouse mutants lacking a notochord the presence of a fused myotome beneath the neural tube has been reported. We have compared the expression pattern of myogenic markers and markers for the hypaxial muscle precursors in the mutants Brachyury curtailed, truncate, Danforth's short tail and Pintail. In regions lacking notochord and sclerotome, we found small, ventrally located domains of Myf5 and MyoD expression, concomitant with ventrally expanded Pax3 signals and upregulated expression of the hypaxial marker Lbx1, suggesting that only the hypaxial program is active. We therefore hypothesise that in mammals, as in birds, the formation of the epaxial musculature depends on the presence of notochord derived signals.
authors.affiliation: King's College London, Department of Craniofacial Development, UK. s.dietrich@umds.ac.uk
authors.forename: S
authors.initials: S
authors.lastname: Dietrich
authors.forename: F R
authors.initials: FR
authors.lastname: Schubert
authors.forename: P
authors.initials: P
authors.lastname: Gruss
authors.forename: A
authors.initials: A
authors.lastname: Lumsden
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics; D005136:Eye Proteins; D005260:Female; D005326:Fetal Proteins; D018507:Gene Expression Regulation, Developmental; D005819:Genetic Markers; D018398:Homeodomain Proteins; D017403:In Situ Hybridization; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009124:Muscle Proteins / Q000235:genetics; D018482:Muscle, Skeletal / Q000196:embryology*; D009154:Mutation; D017570:MyoD Protein / Q000235:genetics; D051787:Myogenic Regulatory Factor 5; D009672:Notochord / Q000502:physiology*; D000072041:PAX3 Transcription Factor; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins; D020825:T-Box Domain Proteins / Q000235:genetics; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics; D000098908:Brachyury Protein
chemical_list: D004268:DNA-Binding Proteins; D005136:Eye Proteins; D005326:Fetal Proteins; D005819:Genetic Markers; D018398:Homeodomain Proteins; D009124:Muscle Proteins; D017570:MyoD Protein; D051787:Myogenic Regulatory Factor 5; D000072041:PAX3 Transcription Factor; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins; D020825:T-Box Domain Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D000098908:Brachyury Protein; C491868:Lbx1h protein, mouse; C497418:Myf5 protein, mouse; C000605732:Pax6 protein, mouse; C068686:Pax3 protein, mouse; C070835:PAX1 transcription factor