Acts partially redundantly with other irx members in neural patterning. Required for formation of the posterior forebrain, midbrain, hindbrain, and to a lesser extent, spinal cord. Acts early in neural plate development to induce expression of some but not all proneural genes, and specify a neural precursor state. Also up-regulates repressors that prevent neuronal differentiation. Patterns the neuroectoderm in both the anterior/posterior and dorsal/ventral axes. Probably dispensable for pronephric kidney development. Expressed in the neural plate in overlapping patterns with other irx members, which all share an anterior border of expression. Also expressed in the placodes. Broadly expressed in the tailbud rhombencephalon (hindbrain). Outside the nervous system and at tailbud stages, expressed in the developing otic vesicle, branchial arches, prospective heart region and pronephros. Belongs to the TALE/IRO homeobox family.