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. Both up-regulates and down-regulates gene expression during neural development. Acts early in neural plate development to induce proneural gene expression and specify a neural precursor state. Also up-regulates repressors that prevent neuronal differentiation. Required during at least two stages of pronephros kidney development; during neurula stages, maintains transcription of key renal genes to define the size and identity of the pronephric anlage, probably in part through regulation of bmp-signaling. Subsequently required for proper formation of the intermediate tubule segment of the pronephros. Expressed in the neural plate in overlapping patterns with other irx members, which all share an anterior border of expression. 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.