Fig. 1. Expression patterns of Irx1 and activin ßA in wild-type heads as seen by DIG whole-mount (A-E) and radioactive section (F-M) in situ hybridisation analyses. (B,C) Frontal vibratome sections through the branchial arches of the embryo in A. (E) Frontal vibratome section through the branchial arches of the embryo in D. At E9.5, DIG-labelled Irx1 probe localises to the branchial arch region (A), labelling the epithelium of the branchial clefts and more posterior arches (C). It is excluded from the oral epithelium of the first branchial arch (B). By E10.5-E11, Irx1 is strongly expressed in the oral epithelium of the first branchial arch (white arrowhead, D; E). Radioactive in situ hybridisation on wax sections was used to analyse the Irx1 expression in the developing teeth at E11 (F,G), E12.5 (J), E13.5 (L) and E14.5 (M). Irx1 expression can be found in the dental epithelia of the incisors (J) and molars (F,G,L,M). Analysis of consecutive serial sections using a 35S-labelled activin ßA probe shows that the expression of these two genes is juxtaposed in the developing teeth. Activin ßA is expressed in the odontogenic mesenchyme underlying the Irx1-positive dental epithelia at E11 (white arrowheads, H) and E12.5 (K). (F,I) Corresponding brightfield illumination of the sections in G,H, respectively, shows the histological detail. ba1, first branchial arch (mandibular process); bc1, first branchial cleft; bc2, second branchial cleft; oe, oral epithelium; mand, mandible; max, maxilla; tg, tongue.
