Fig. 3.

Whole-mount in situ hybridization in E3.5 to E4.5 chicken control and surgically altered embryos. (A–I) Fgf8, Bmp4, and Pitx1 mRNAs are present in the oral epithelium and ectoderm of BA1 in control (A–C) and forehead-excised embryos after 8-ss (G–I) but not in embryos whose foreheads were excised at 6-ss (D–F). (J–L) Embryos whose foreheads were excised at 6-ss and replaced by a Shh bead show patterns of expression of those genes (black arrows) and a well developed BA1 (‘1’), in contrast to nontreated embryos, which exhibit a reduced sized BA1 and misexpression of these genes (D–F). An asterisk marks the expression of Pitx1 in the suborbital zone in F. In the absence of eyes, the two foci of expression join in a single transversal spot.