Fig. 7. A model for cranial paraxial mesoderm specification in the chick embryo. Our model proposes that cells within the CPM that migrate through the first branchial arch (marked by orange line), first adopt a myogenic lineage (Myf5, Capsulin and Tbx1; highlighted in the upper box). Those cells migrating further towards the aortic sac, which connects the branchial arches to the OFT, initiate cardiogenesis (note the expression of cardiac markers Gata5, Gata6, Capsulin, Isl1 and Nkx2.5; middle box). A smaller portion of these cells may reach the myocardium and endocardium of the OFT, where different cardiac markers are expressed (e.g. Gata4 and cMHC; lower box). The gradual shift from a skeletal muscle to a cardiac cell fate is correlated with the spatiotemporal expression of Bmp4. Moreover, ectopic application of Bmp4 both in vitro and in vivo promotes cardiogenesis in the cranial paraxial mesoderm, and blocks the skeletal muscle differentiation programs.