title: Tbx1 regulation of myogenic differentiation in the limb and cranial mesoderm.
abstract: The T-box transcription factor Tbx1 has been implicated in DiGeorge syndrome, the most frequent syndrome due to a chromosomal deletion. Gene inactivation of Tbx1 in mice results in craniofacial and branchial arch defects, including myogenic defects in the first and second branchial arches. A T-box binding site has been identified in the Xenopus Myf5 promoter, and in other species, T-box genes have been implicated in myogenic fate. Here we analyze Tbx1 expression in the developing chick embryo relating its expression to the onset of myogenic differentiation and cellular fate within the craniofacial mesoderm. We show that Tbx1 is expressed before capsulin, the first known marker of branchial arch 1 and 2 muscles. We also show that, as in the mouse, Tbx1 is expressed in endothelial cells, another mesodermal derivative, and, therefore, Tbx1 alone cannot specify the myogenic lineage. In addition, Tbx1 expression was identified in both chick and mouse limb myogenic cells, initially being restricted to the dorsal muscle mass, but in contrast, to the head, here Tbx1 is expressed after the onset of myogenic commitment. Functional studies revealed that loss of Tbx1 function reduces the number of myocytes in the head and limb, whereas increasing Tbx1 activity has the converse effect. Finally, analysis of the Tbx1-mesoderm-specific knockout mouse demonstrated the cell autonomous requirement for Tbx1 during myocyte development in the cranial mesoderm.
authors.affiliation: Department of Craniofacial Development, King's College London, Guy's Tower, London Bridge, United Kingdom.
authors.forename: Akbar
authors.initials: A
authors.lastname: Dastjerdi
authors.forename: Lesley
authors.initials: L
authors.lastname: Robson
authors.forename: Rebecca
authors.initials: R
authors.lastname: Walker
authors.forename: Julia
authors.initials: J
authors.lastname: Hadley
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.forename: Marc
authors.initials: M
authors.lastname: Rodriguez-Niedenführ
authors.forename: Paris
authors.initials: P
authors.lastname: Ataliotis
authors.forename: Antonio
authors.initials: A
authors.lastname: Baldini
authors.forename: Peter
authors.initials: P
authors.lastname: Scambler
authors.forename: Philippa
authors.initials: P
authors.lastname: Francis-West
mesh_terms: D000818:Animals; D002642:Chick Embryo; D047108:Embryonic Development / Q000502:physiology*; D005121:Extremities / Q000196:embryology*; D005152:Facial Muscles / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental; D005822:Genetic Vectors / Q000235:genetics; D017403:In Situ Hybridization; D008648:Mesoderm / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D032448:Myoblasts, Skeletal / Q000378:metabolism / Q000502:physiology*; D012190:Retroviridae; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D020825:T-Box Domain Proteins; C491573:Tbx1 protein, mouse