Expressed in specific and overlapping patterns with Irx1 and Irx3 in the developing and adult metanephric kidney. In the adult metanephros, renal expression is found in the loop of Henle in the S3 proximal tubule segment and in the thick ascending limb (TAL) of the distal tubule. First expressed at 8.0 dpc. During neural tube closure (8.5 dpc), expression appears for the first time in the rhombencephalon in the presumptive region of future rhombomere 4. During neurogenesis (9.5 dpc to 10.5 dpc), predominantly expressed along the anteroposterior axis of the CNS in the mesencephalon, metencephalon and rhombencephalon. Expression is strong in the tectum of the mesencephalon and in the hindbrain, expression is restricted to rhombomeres. Expression in the spinal cord is weak and confined to the alar plate. Beginning at 9.5 dpc, expressed in the epithelial component of the branchial arches and foregut. At 10.5 dpc, expression extends rostrally into the dorsal diencephalon. Starting at the otic vesicle stage, shows regionalized expression in the developing inner ear with expression in the entire otic vesicle from 10.5 dpc onwards. From 10.5 dpc onwards, weak expression begins in the limb bud. Also expressed in other tissues during organogenesis; at 9.5 dpc, expressed in the superficial ectoderm surrounding the body and in the region of the foregut, which will form the pharynx and the lung bud. at 10.5 dpc, found in the cephalic mesenchyme around the optic vesicle. By 12.5 dpc, still expressed in the mesenchyme, and expression begins in specific subsets of post-mitotic cells in the neuroretina. As development ensues, expression increases in the neuroretina and mesenchymal expression gradually decreases. At 16.5 dpc, expressed exclusively in the inner neuroblast layers of the neuroretina. Expressed in the developing heart in the ventricular septum from the onset of its formation (10.5 dpc) onward. In fetal stages, expression becomes confined to the myocardium of the atrioventricular bundle and bundle branches of the forming ventricular conduction system. Belongs to the TALE/IRO homeobox family. Called Irx6 by PubMed:10704856.