HOX genes play a fundamental role in the development of the vertebrate central nervous system, heart, axial skeleton, limbs, gut, urogenital tract and external genitalia. There are multiple transcripts of the Hoxb3 gene, and the anterior boundaries of its expression vary at different stages of development. Hoxb3 plays a role in the proliferation and differentiation of both early myeloid and lymphoid developmental pathways. Hoxb3 also has overlapping function in mediating the migration of pharyngeal organ primordia and is expressed in very restricted domains in the future hindbrain. Hoxb6 controls the generation, proliferation and survival of erythroid progenitor cells. The Hoxb6 protein is expressed in the suprabasal layer of the early developing epidermis and throughout the upper layers of late fetal and adult human skin. Hoxb6 is cytoplasmically expressed throughout fetal epidermal development, but displays nuclear expression in normal adult skin. Hoxb6 protein also has nuclear expression in hyperproliferative skin conditions, but appears to be localized in the cytoplasm in basal and squamous cell carcinomas. Hoxb6 genes are also expressed in normal adult lung.