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. At stage 20, expressed in a subset of cells in the developing hindbrain with expression appearing above the otic vesicle by stage 26. Expression in retina cells begins at stage 28, continuing at later stages and is limited to a subset of retinal cells of the optic cup. Also expressed in the ventricle of the heart from stage 36 (late tailbud) onwards. Only expressed in the pronephros at tadpole stage. Belongs to the TALE/IRO homeobox family.