Essential for pronephric tubule development, acting upstream of pax8 and lhx1/lim1 and downstream of retinoic acid signaling to induce pronephric mesoderm to form pronephric tubule-specific cells. Expressed in prospective pronephric mesoderm at the late gastrula stage. After neurulation, expressed in the intermediate mesoderm, eye placode and blood islands. Expression becomes restricted to the pronephric proximal tubule during embryogenesis, but is absent from the connecting tubules. Expressed zygotically from late gastrula stages, persisting throughout embryogenesis with highest expression between stages 30 and 35. By retinoic acid.