Involved in epithelial-mesenchymal interactions in kidney and lung morphogenesis that include epithelial differentiation and branching morphogenesis. Efficient DNA binding requires dimerization with another bHLH protein. Expressed in the cranial paraxial mesoderm from 20 hpf and subsequently becomes restricted to the pharyngeal mesoderm that will form the muscle. Expression in the proepicardial organ is first seen at 40hpf in a cluster of cells between the myocardium and yolk. Also expressed in the developing arches. Expression begins to surround the heart by day 3 of development, and by 96 hpf, expression is restricted to the outer epicardial layer surrounding the myocardium.