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. Patterns the neuroectoderm in both the anterior/posterior and dorsal/ventral axes. Does not appear to play a role in pronephros kidney development. Expressed in the neural plate in overlapping patterns with other irx members, which all share an anterior border of expression. Broadly expressed in the tailbud rhombencephalon (hindbrain). Outside the nervous system and at tailbud stages, expressed in the developing otic vesicle, branchial arches and prospective heart region. Belongs to the TALE/IRO homeobox family.