Fig. 5. The initiation of the ventral pancreatic development is not affected in Flk1^-/- embryos. (A-F) Immunostaining of transverse sections of control (upper row) and Flk1^-/- (lower row) embryos at E9.0-10.0 (somite stages are indicated on the top of each panel) with Pecam (A,B) and Pdx1 (C-F) antibodies. No endothelial cells or blood vessels were detected in Flk1^-/- embryos (B). Blue arrowhead denotes a possible extraembryonic cell (see text) staining positive for Pecam; these were occasionally detected and were reported by Shalaby et al. (Shalaby et al., 1995). (G) RT-PCR analysis of Pecam and Tal1 expression in ventral midgut/pancreatic bud tissue. Note faint bands in lanes 10 and 12 (Flk1 homozygotes). (H) RT-PCR analysis of the ventral region of control and Flk1^-/- embryos. PCR cycle ranges similar to that in Fig. 4A. Note the induction of Ptf1a, but not of glucagon. Insulin is not normally detectable ventrally at these stages (data not shown).