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First published online 15 November 2006
doi: 10.1242/dev.02693
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1 Institute of Biosciences and Technology, Texas A&M System Health Science
Center, 2121 Holcombe Blvd, Houston, TX 77030, USA.
2 Department of Craniofacial Development, King's College, London Guy's Tower,
London SE1 9RT, UK.
3 Program in Cardiovascular Sciences, Department of Medicine, Baylor College of
Medicine, One Baylor Plaza, Houston, TX 77030, USA.
* Author for correspondence (e-mail: jmartin{at}ibt.tamhsc.edu)
Accepted 12 October 2006
Recent experiments, showing that both cranial paraxial and splanchnic mesoderm contribute to branchiomeric muscle and cardiac outflow tract (OFT) myocardium, revealed unexpected complexity in development of these muscle groups. The Pitx2 homeobox gene functions in both cranial paraxial mesoderm, to regulate eye muscle, and in splanchnic mesoderm to regulate OFT development. Here, we investigated Pitx2 in branchiomeric muscle. Pitx2 was expressed in branchial arch core mesoderm and both Pitx2 null and Pitx2 hypomorphic embryos had defective branchiomeric muscle. Lineage tracing with a Pitx2cre allele indicated that Pitx2 mutant descendents moved into the first branchial arch. However, markers of both undifferentiated core mesoderm and specified branchiomeric muscle were absent. Moreover, lineage tracing with a Myf5cre allele indicated that branchiomeric muscle specification and differentiation were defective in Pitx2 mutants. Conditional inactivation in mice and manipulation of Pitx2 expression in chick mandible cultures revealed an autonomous function in expansion and survival of branchial arch mesoderm.
Key words: Homeobox, Branchiomeric muscle, Mouse, Chick
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