Fig. 4. Fgf10^–/– embryos have a small pancreatic primordium because the Pdx1-expressing epithelial progenitor cell population is not maintained. Dorsal is to the right. (A) Pdx1 is expressed uniformly in undifferentiated cells throughout the developing pancreatic buds in wild-type embryos at E10.5 (B) Immunofluorescence analysis of PDX1 expression in transverse section of an E10.5 wild-type embryo shows the buds emerging from the foregut. (C) By 12.5, Pdx1 expression is no longer uniform (due to differentiation of precursor cells) and the branching of the epithelium is evident in the dorsal bud. (D) By E13.5, Pdx1 expression is increasingly restricted within the epithelium and accentuates the lobulated structure of both the pancreatic buds. As compared to the wild-type littermates the Pdx1 expression in the Fgf10^–/– embryos at E10.5 (E) identifies the formation of two small but distinct pancreatic buds. (F) Immunofluorescence analysis confirmed the reduced expression of PDX1 in these two pancreatic buds in mutant embryos. Pdx1 expression is no longer observed later in development at E12.5 (G) and E13.5 (H). Arrows indicate the area within the gut where the pancreatic buds normally form. Occasionally, some weak expression of Pdx1 was observed in the ventral bud of mutant embryos (H). v, ventral; d, dorsal.