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. Involved in craniofacial and gonadal development. Modulates the migration of progenitor cell populations in branchial arches and gonads by repressing CXCL12. Early in gastrulation, expressed in cells beneath the blastopore lip. Subsequently expressed in the neural plate in overlapping patterns with other irx members, which all share an anterior border of expression. At the time of neural tube closure (stage 19) in regions of the midbrain, hindbrain, neural tube and optic vesicle, where expression continues during tailbud stages. In stage 34, expressed throughout the eye retina. Does not appear to be expressed in the developing heart or pronephros. By hoxb4 and hoxb5. Down-regulated by hoxb9. Belongs to the TALE/IRO homeobox family.