Wnt/Lef1 signaling acts via Pitx2 to regulate somite myogenesis.
Wnt signaling has been implicated in somite, limb, and branchial arch myogenesis but the mechanisms and roles are not clear. We now show that Wnt signaling via Lef1 acts to regulate the number of premyogenic cells in somites but does not regulate myogenic initiation in the limb bud or maintenance in the first or second branchial arch. We have also analysed the function and regulation of a putative downstream transcriptional target of canonical Wnt signaling, Pitx2. We show that loss-of-function of Pitx2 decreases the number of myogenic cells in the somite, whereas overexpression increases myocyte number particularly in the epaxial region of the myotome. Increased numbers of mitotic cells were observed following overexpression of Pitx2 or an activated form of Lef1, suggesting an effect on cell proliferation. In addition, we show that Pitx2 expression is regulated by canonical Wnt signaling in the epaxial somite and second branchial arch, but not in the limb or the first branchial arch. These results suggest that Wnt/Lef1 signaling regulates epaxial myogenesis via Pitx2 but that this link is uncoupled in other regions of the body, emphasizing the unique molecular networks that control the development of various muscles in vertebrates.
University of East Anglia, School of Biological Sciences, Norwich, NR4 7TJ Earlham Road, UK.
Muhammad
M
Abu-Elmagd
Lesley
L
Robson
Dylan
D
Sweetman
Julia
J
Hadley
Philippa
P
Francis-West
Andrea
A
Münsterberg
D000818:Animals; D001934:Branchial Region / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D002452:Cell Count; D002454:Cell Differentiation; D049109:Cell Proliferation; D002645:Chickens; D005121:Extremities / Q000196:embryology; D018390:Gene Targeting; D018398:Homeodomain Proteins / Q000378:metabolism*; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000378:metabolism*; D051379:Mice; D024510:Muscle Development / Q000502:physiology*; D011485:Protein Binding; D015398:Signal Transduction; D019170:Somites / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D051153:Wnt Proteins / Q000378:metabolism*; D000097577:Homeobox Protein PITX2
D018398:Homeodomain Proteins; D051821:Lymphoid Enhancer-Binding Factor 1; D014157:Transcription Factors; D051153:Wnt Proteins; D000097577:Homeobox Protein PITX2