Whole-mount in situ hybridization was performed in E12.5 wild-type (A, a, D, d, G, g, J, j, M, m), Hand1NCKO/KO;Hand2KO/+ (B, b, E, e, H, h, K, k, N, n) and Hand1NCKO/KO;Hand2BA/BA (C, c, F, f, I, i, L, l, O, o) embryos. Frontal views (upper case) and transverse oral views (lower case) are shown. Pax9 is expressed in the dental and inter-dental (arrow in a) mesenchyme of the wild-type embryos, however, inter-dental expression is absent in both mutant embryos (arrows in b, c). Msx2 is expressed in the incisors (arrows in g) and Prx2 is expressed in the distal midline mesenchyme of wild-type embryos (arrow in m). In both mutants, Msx2 and Prx2 are down-regulated (arrows in h, i, arrow in n, o). Other candidate marker genes, Msx1 and Prx1, showed no remarkable changes.