Fig. 6. Wnt7a is expressed in the developing organ of Corti. (A) Whole-mount in situ hybridization for Wnt7a in the cochlear duct at E14. A band of Wnt7a expression is present in the basal region (base) of the cochlea (arrow). In the apical turn (apex) of the cochlea, Wnt7a expression spans most of the width of the floor of the cochlear duct. Box near base indicates the region of the epithelium illustrated in B. Box near apex indicates region illustrated in C. (B) Cross-section through the apical turn of the cochlea at E14. For all cross-sections, inner is towards the left (Mod in E), outer is towards the right (Str in E). There is broad expression of Wnt7a throughout the epithelium. However, there is a distinct boundary of Wnt7a expression (arrow) that correlates with the spiral vessel (asterisk), an embryonic marker for the location of the developing organ of Corti. (C) Cross-section through the basal region of the cochlear duct at E14. Wnt7a expression persists in a band of cells that extends from the boundary at the spiral vessel (arrow) towards the inner-side of the duct (arrowhead). In addition, Wnt7a is still expressed in some cells located at the inner edge of the duct. (D) Whole-mount in situ hybridization for Wnt7a at E16. By this stage, expression of Wnt7a is restricted to a band of cells that extends along the length of the cochlea (arrows) from base to apex. Box indicates region illustrated in E. (E) Cross-section through the basal region of the cochlear duct at E16. Expression of Wnt7a is restricted to developing pillar cells (arrow) located directly above the spiral vessel (asterisk). (F) Cross-section through the cochlear duct at P0. Wnt7a expression persists in the inner and outer pillar cells (arrow), with the possibility of a small amount of expression in the Deiter's cell located underneath the first row OHC (1). Second (2) and third (3) row OHC are numbered for reference. Scale bars: 100 µm in A,D; in F, 20 µm for B,C,E,F.