Fig. 9. The dynamic location of events in accretion of myocardium to the outflow
tract from the secondary heart field. The splanchnic mesoderm expresses Gata-4
and Nkx2.5. The outflow tract moves craniocaudally across this mesoderm. As
the outflow tract approaches, Gata-4/Nkx2.5-positive cells begin to express
HNK-1, move into the outflow tract, and begin to express MF20. FGF-8 expressed
at the lateral sides of the pharyngeal arches may cause proliferation of the
cells in the secondary heart field, while BMP-2 expressed by the distal
outflow myocardium and secondary heart field near the outflow tract induce
expression of the contractile proteins in the cells being incorporated into
the outflow myocardium.
