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 expr essed during mouse development in the inner ear. Here, we present the detailed expression of both genes within the developing ear and a comp arison to the expression of other potential control genes in this orga n. Both genes are active between E13.5 and birth in non-sensory epithe lium of the semicircular canals, utricle and saccule. Nkx5-1 and Nkx5- 2 are also expressed in the cochlea, where the expression is restricte d to the stria vascularis. The endolymphatic duct is devoid of any Nkx 5 transcripts. Pax2 is expressed in epithelial cells of the ventral pa rt of the membranous labyrinth where it overlaps with the Nkx5 express ion domain. sek shows a complementary pattern to Nkx5 in the vestibula r epithelium. In the cochlea sek is expressed throughout the mesenchym e and epithelium but not in the stria vascularis. In the vestibulum Pa x2 and sek is limited to the ventral part whereas Nkx5 genes are activ e thoroughout. These data suggest that Nkx5 genes, Pax2 and sek play d ifferent roles in the patterning of inner ear structures.