Regionalized expression of Nkx5-1, Nkx5-2, Pax2 and sek genes during mouse inner ear development.

Nkx5-1 and Nkx5-2 are two highly related homeobox genes which are expressed during mouse development in the inner ear. Here, we present the detailed expression of both genes within the developing ear and a comparison to the expression of other potential control genes in this organ. Both genes are active between E13.5 and birth in non-sensory epithelium of the semicircular canals, utricle and saccule. Nkx5-1 and Nkx5-2 are also expressed in the cochlea, where the expression is restricted to the stria vascularis. The endolymphatic duct is devoid of any Nkx5 transcripts. Pax2 is expressed in epithelial cells of the ventral part of the membranous labyrinth where it overlaps with the Nkx5 expression domain. sek shows a complementary pattern to Nkx5 in the vestibular epithelium. In the cochlea sek is expressed throughout the mesenchyme and epithelium but not in the stria vascularis. In the vestibulum Pax2 and sek is limited to the ventral part whereas Nkx5 genes are active throughout. These data suggest that Nkx5 genes, Pax2 and sek play different roles in the patterning of inner ear structures.