Figure 3. Sox9 is dispensable for pancreas induction.

(A,C) Confirmation of global Sox9 deletion by WMIF staining of Sox9 in E10.5 tail-tips. (B,D) 2D projections of 3D Imaris-reconstructed z-stacks through trunks of embryos after WMIF for Foxa2 and Pdx1. Although smaller, dorsal and ventral pancreatic buds are present in E10.5 Sox9-null embryos (D,D′). Fields demarcated by white dashed boxes in B,D are shown at higher magnification in B′,D′, respectively. Only single-channel Pdx1 signal is shown in B′ and D′. (E–H″) Immunofluorescence staining of sections through the pancreatic region of Sox9^fl/fl;Foxa3-Cre (Sox9^Δgut/Δgut) and control Sox9^fl/fl embryos at E9.5. Sox9 is efficiently deleted in dorsal (G′,G″) and ventral (H′,H″) pancreatic buds of Sox9^Δgut/Δgut embryos. Dashed line in G′ and H′ demarcates the Pdx1⁺ domain. (I–T) X-Gal staining for β-galactosidase expressed from the Pdx1^LacZko allele in embryonic day (E) 10.5 and E12.5 embryos carrying combinations of mutant alleles for Pdx1 and Sox9. With increasing loss of Sox9 dosage on either Pdx1-heterozygous (I–N) or Pdx1-null (O–T) backgrounds, dorsal and ventral pancreatic buds become increasingly hypoplastic. In Pdx1^−/−;Sox9^Δgut/Δgut embryos (S,T), pancreatic buds are not discernible. Note the reduced ventral pancreas in E12.5 compound heterozygous mutants (L). Asterisks denote absence of ventral pancreas. (U) With decreasing dosage of functional Pdx1 and Sox9 alleles, pancreatic morphogenesis becomes increasingly perturbed. dp, dorsal pancreas; vp, ventral pancreas; duo, duodenum; stom, stomach; li, liver; bd, bile duct. Scale bars = 50 μm (E–H″), 70 μm (B,B′,D, D′), 200 μm (A,C), 250 μm (I–T).