In situ hybridization on 12μm transverse sections through the otocyst of stage 13 (A-E), stage 18 (F-J), and stage 24 (K-O) chick embryos using probes for Pax2 (A, F, K), Zic1 (B, G, L), Zic2 (C, H, M), Zic3 (D, I, N), and Zic4 (E, J, O). Note that Pax2 is expressed in sensory regions of the otic epithelium, while Zic gene expression is restricted to the surrounding mesenchyme. Abbreviations: oe, otic epithelium; ed, endolymphatic duct; nt, neural tube; sag, statoacoustic ganglion; hv, head vein; d, dorsal; m, medial. Asterisks identify Zic expression in the neural tube (B, C, D, G, H, I, J, L, M, N, O). Black arrowheads indicate Zic-expressing cells between the outer epithelium and the otic epithelium (G, H, I, L, M, N). Yellow arrow indicates Zic-expressing cells between neural tube and otic epithelium (G, H). Red arrowheads indicate the ventral-most extent of Zic expression in the mesenchyme (L, M, N, O). Scale bar in A, 50μm (applies to A-J); scale bar in K, 100μm (applies to K-O).