Transcription factor involved in specification of neuronal cell types and which is required for inner ear and hypothalamus development. Binds to the 5'-CAAGTG-3' core sequence. Controls semicircular canal formation in the inner ear. Also required for hypothalamic/pituitary axis of the CNS. Expressed in the developing CNS, including a specific expression in vestibular structures throughout inner ear development. Begins at embryonic day 10.5 in the developing ear, hypothalamus, the neural tube and dorsal root ganglia. It continues to be active throughout prenatal life in discrete regions of the brain with an anterior border in the ventral diencephalon at the optic chiasma and expression domains in mesencephalon, metencephalon, and myelencephalon. At midgestation, it is also expressed in mesenchyme of the head and branchial arches, and in some cranial ganglia, as well as in derivatives of neural crest, such as the truncus sympathicus and myenteric ganglia. In inner ear, it is expressed between 13.5 dpc and birth in non-sensory epithelium of the semicircular canals, utricle and saccule. Also expressed in the cochlea, where the expression is restricted to the stria vascularis. Regulated by Six1 and FGFs in inner ear. Mice display abnormal circling behavior and severe vestibular defects owing to a depletion of sensory cells in the saccule and utricle, and a complete loss of the horizontal semicircular canal crista, as well as a fusion of the utricle and saccule endolymphatic spaces into a common utriculosaccular cavity. Moreover, most females have a reproductive defect: females can be fertilized and their embryos undergo normal preimplantation development, but the embryos fail to implant successfully in the uterus and subsequently die. Mice lacking both Hmx2 and Hmx3 show a complete loss of balance, postnatal dwarfism, defects in neuroendocrine system, disturbed hypothalamic-pituitary axis and subsequent die. Defects caused in mice lacking both Hmx2 and Hmx3 can be rescued by expressing the Drosophila Hmx protein. Belongs to the HMX homeobox family. Chimeric cDNA.