The Hmx homeobox gene family is of ancient origin, being present in sp
ecies as diverse as Drosophila, sea urchin and mammals, The three memb
ers of the murine Hmx family, designated Hmx1, Hmx2 and Hmx3, are expr
essed in tissues that suggest a common functional role in sensory orga
n development and pregnancy, Hmx3 is one of the earliest markers for v
estibular inner ear development during embryogenesis, and is also upre
gulated in the myometrium of the uterus during pregnancy, Targeted dis
ruption of the Hmx3 gene results in mice with abnormal circling behavi
or and severe vestibular defects owing to a depletion of sensory cells
in the saccule and utricle, and a complete loss of the horizontal sem
icircular canal crista, as well as a fusion of the utricle and saccule
endolymphatic spaces into a common utriculosaccular cavity. Both the
sensory and secretory epithelium of the cochlear duct appear normal in
the Hmx3 null animals, The majority of Hmx3 null females have a repro
ductive defect. Hmx3 null females can be fertilized and their embryos
undergo normal preimplantation development, but the embryos fail to im
plant successfully in the Hmx3 null uterus and subsequently die. Trans
fer of preimplantation embryos from mutant Hmx3 uterine horns to wild-
type pseudopregnant females results in successful pregnancy, indicatin
g a failure of the Hmx3 null uterus to support normal post-implantatio
n pregnancy, Molecular analysis revealed the perturbation of Hmx, Wnt
and LIF gene expression in the Hmx3 null uterus, Interestingly, expres
sion of both Hmx1 and Hmx2 is downregulated in the Hmx3 null uterus, s
uggesting a hierarchical relationship among the three Hmx genes during
pregnancy.