Iroquois-class homeodomain protein IRX-3, also known as Iroquois homeobox protein 3, is a protein that in humans is encoded by the IRX3 gene.^[5]

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IRX3
Identifiers
Aliases	IRX3, IRX-1, IRXB1, iroquois homeobox 3
External IDs	OMIM: 612985 MGI: 1197522 HomoloGene: 7385 GeneCards: IRX3
Gene location (Human) Chr. Chromosome 16 (human)[1] Band 16q12.2 Start 54,283,304 bp[1] End 54,286,787 bp[1]
Gene location (Mouse) Chr. Chromosome 8 (mouse)[2] Band 8 C5|8 44.55 cM Start 92,525,153 bp[2] End 92,528,695 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in nipple human penis bronchial epithelial cell vulva lactiferous duct trachea right ventricle renal medulla urethra skin of abdomen Top expressed in lacrimal gland left lung lobe maxillary prominence calvaria abdominal wall right lung right lung lobe right ventricle myocardium of ventricle cochlea More reference expression data BioGPS n/a
Gene ontology Molecular function sequence-specific DNA binding DNA binding DNA-binding transcription factor activity, RNA polymerase II-specific Cellular component cytoplasm axon nucleus Biological process multicellular organism development mesoderm development specification of loop of Henle identity metanephros development regulation of transcription, DNA-templated negative regulation of neuron differentiation positive regulation of neuron differentiation transcription, DNA-templated proximal/distal pattern formation involved in nephron development regulation of transcription by RNA polymerase II energy homeostasis Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 79191 16373 Ensembl ENSG00000177508 ENSMUSG00000031734 UniProt P78415 P81067 RefSeq (mRNA) NM_024336 NM_001253822 NM_008393 RefSeq (protein) NP_077312 NP_001240751 NP_032419 Location (UCSC) Chr 16: 54.28 – 54.29 Mb Chr 8: 92.53 – 92.53 Mb PubMed search [3] [4]
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The Iroquois family of genes was discovered in Drosophila during a mutagenesis experiment designed to identify genes that affected the development of external sensory organs. When genes of this family were knocked out, the Drosophila flies expressed a unique patterning of bristles reminiscent of Iroquois American Indians, they were subsequently named after them.^[6] The molecular characteristics of these genes allowed the identification of homologs in C. elegans and several other vertebrates.^[7]

IRX3 is a member of the Iroquois homeobox gene family and plays a role in an early step of neural development.^[8] Members of this family appear to play multiple roles during pattern formation of vertebrate embryos.^[5][9] Specifically, IRX3 contributes to pattern formation in the spinal cord where it translates a morphogen gradient into transcriptional events, and is directly regulated by NKX2-2.^[10] The Irx3 gene controls the subdivision of the neural territory by working together with various other homeodomain factors, all of these factors are expressed in partially overlapping domains along the dorsoventral axis in response to Sonic hedgehog molecules emanating from the floor plate. The combination of these signals defines five regions, each of which will give rise to five types of neurons (V0, V1, V2, MN, and V3). For example, the region that generates V2 neurons expresses both Irx3 and Nkx6.1, while that which forms MN neurons expresses Nkx6.1 alone. Irx3 overexpression in the MN domain transforms MN into V2 neurons.^[11]