Fig. 4. Depletion of the definitive gut endoderm in Sox17–/– embryos. (A-D) Hnf3
expression in the definitive gut endoderm of the 8.5 (A,C) and 9.5 (B,D) dpc normal and mutant embryos [A includes both anterior (left) and posterior (right) views of the same embryos]. Hnf3 expressing cells are confined to a much narrower medial and paraxial domain in the embryonic gut of the mutant embryo. (E) Transverse sections of 9.5 dpc embryos demonstrate normal Hnf3ß expression pattern in the reduced hindgut endoderm and the floor plate of the heterozygous (+/–) and null mutant (–/–) embryos. (F,G) 9.5 dpc mutant (–/–) embryos showing normal Cdx2 expression in the endoderm of the gut posterior to the level marked by the red arrow (F, lateral view; G, transverse section at the plane indicated by the broken line in F). (H,I) Hex expression in the foregut endoderm of 8.5 dpc embryos (H; anterior view) and in the thyroid (small arrows) and liver (large arrows) buds of 9.5 dpc embryos (I; lateral view). (J) Pdx1 expression in dorsal (small arrow) and ventral (large arrow) pancreatic regions of the gut endoderm in 9.5 dpc heterozygous embryos (left-most in the figure). Pdx1 expression is completely absent (broken arrows) in the prospective pancreatic tissues of the homozygous (–/–) mutant embryos (two on the right hand side). (K-P) Shh expression in the definitive gut endoderm (open arrows for foregut, solid arrows for mid to hindgut) and notochord of 8.5 (K, posterior view; L,M, transverse sections) and 9.5 dpc embryos (N, lateral view; O,P, transverse sections). In plate P, the broken arrow shows the Shh-negative posterior gut in the mutant (–/–) embryo. (Q,R) Ihh expression in the visceral and definitive endoderm of 8.5 (Q; ventral view) and 9.5 (R; lateral view) dpc embryos. The unbroken arrows indicate the Ihh-positive endoderm in the heterozygous embryo and the broken arrows indicate the absence of Ihh expression in the equivalent endodermal tissues in the homozygous mutant embryo. (S,T) Ptch expression in the ventral structures of the 8.5 dpc mutant embryos (S, ventral view; T, transverse section). The unbroken arrows indicate the Ptch-positive splanchnic mesothelium in the heterozygous embryo and the broken arrows indicate the absence of Ptch expression in the equivalent tissues in the homozygous mutant embryo. Broken lines on the whole-mount figures show the plane of histological sections. Arrowheads in C,H,M,T indicate the border between the presumptive visceral endoderm and the definitive endoderm. fg, foregut; fp, floor plate; hg, hindgut; nc, notochord; mes, mesothelium; ve, visceral endoderm; asterisk, nonspecific signals that are due to antibody trapping in lumen. Scale bars: 100 µm.
