Fig. 3. Ventral pancreas is not specified in Hex^-/- embryos. (A,B) Sagittal sections comparing the Pdx1 and Hex expression domains in wild-type embryos. The Pdx1-positive domain in the ventral endoderm (A) corresponds to the most anterior-ventral positive domain of Hex-positive cells (purple staining in B). Pdx1-positive cells also occur in the dorsal pancreatic endoderm. (C,E) lacZ expression in a Hex^+/- embryo. (C) Note the caudal extension of the blue lacZ-positive cells. Arrow indicates level of section in D. (D) Transverse section of the embryo in C immunostained for Pdx1; the boxed region is magnified in E. (E) Cells doubly positive for Pdx1 (nuclear, dark) and Hex^lacZ (cytoplasmic, blue) are present in the ventral endoderm of the gut. (F,G) In situ hybridization for Pdx1. Arrows point to Pdx-positive cells at the exit of the foregut (as in A). (H) RT-PCR analysis of Ptf1^p48 in ventral foregut endoderm from 12-16S embryos of the designated genotypes. The lowest panel depicts endogenous Hex expression. (I-T) Immunohistochemical staining for designated markers. Complete section series of three to four embryos were analyzed for each stage and marker, all with the same results as those shown. Dashed arrow indicates regions where pancreatic genes or cells would normally occur, but where they are absent in Hex-null embryos. Original magnifications: I-L, O-R, 200x; M, N, 100x; S, T, 40x. No evidence for pancreatic gene expression or morphogenesis was detected ventrally in Hex^-/- embryos.