Figure 9.

Schematic summary: differential effects of Pdx1 dosage on pancreas and foregut epithelial development. The previous protein-null (Offield et al. 1996) and ΔI-II-III alleles are represented. Homozygous protein-null embryos frequently lack villi in the rostral-most duodenum (their variable presence indicated by lighter shading and dotted lines), with severe pyloric dysmorphology (light-orange plug). Brunner's glands are absent from the duodenal collar region adjacent to the pylorus. Not represented here is the enteroendocrine cell deficiency in stomach and duodenum (see text). One copy of the partially functional ΔI-II-III allele restores differentiation of the pylorus, Brunner's glands, and rostral duodenal villi, but the pancreas remains highly abrogated (Figs. 3, 4). Embryos homozygous for the ΔI-II-III allele exhibit quasi-pancreatic differentiation of a dorsal bud-derived pancreatic rudiment proximal to the gut tube, and a distal cystic epithelium (Fig. 4). (Blue dots) Lack of ventral bud specification as marked by Ptf1a-Cre;R26R lineage tracing (Fig. 3). The Δ/+ combination allows full-sized outgrowth of both dorsal and ventral buds, but the islets are highly abnormal (Fig. 7). (Yellow) Acini and Brunner's glands; (red) glucagon-producing α cells; (green) insulin-producing β cells.