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. At the start of neurulation (stage 13), expressed in the pronephros. At tailbud stage (stage 25-28), expression is high in the anterior-most branchial arch and pronephric glomus. At stage 40, staining persists in the glomus and in the epicardium region of the heart, and at stage 42, expression is higher in the glomus than in the kidney tubule or duct. In adults, expression is highest in the rectum and the spleen, with significant expression in the duodenum, heart, kidney, lungs, pancreas, skin, liver and muscle. Expression begins at the start of neurulation (stage 13), followed by a gradual increase in expression from stages 16.5 to 26.5, after which expression levels are maintained through to stage 35.