goosecoid expression represses Brachyury in embryonic stem cells and affects craniofacial development in chimeric mice.

The homeobox gene goosecoid, originally identified in Xenopus, is expressed in the organizer or its equivalent during gastrulation in the frog, chick, zebrafish and mouse. To investigate the role of goosecoid in mouse development, we have generated embryonic stem cells that stably overexpress the murine homolog of goosecoid. These cells show a repression of the gastrulation-associated gene Brachyury. Interestingly, repression of Brachyury is conserved between Xenopus and mouse despite the lack of conservation of the Brachyury promoter. Further characterization of the goosecoid-overexpressing ES cells revealed that they maintain the expression of stage-specific embryonic antigen-1, and teratomas derived from goosecoid-overexpressing cells show the presence of cell types derived from all three germ layers. Some highly chimeric mice derived from goosecoid-overexpressing cells displayed skull defects. These observations suggest that goosecoid may play a role in specification of anterior mesendodermal fates and specifically in mouse craniofacial development.