Probable transcription factor with a role in initial mesoderm differentiation. Efficient DNA binding requires dimerization with another bHLH protein. Homodimer (By similarity). In late gastrula embryos, expressed in the presumptive first pair of somites and the middorsal wall of the primitive gut. Expression is then up-regulated in the lateral wall of the somites and the notochord. At the late neurula stage, also expressed in the anterior wall of the primitive gut and in the evaginating lateral diverticula. In the earliest larval stage, expression is restricted to both ends of the body. In 36 hour larvae, only faint expression is detected in the notochordal and paraxial mesoderm of the caudal region. Expressed in late gastrulae stage G6 to larval stage L2.