vHNF1 is required for the formation of endoderm derivatives in zebrafish. (A-T) Whole-mount in situ hybridization in dorsal (A-D,G-L,Q-R), lateral (E,F), or ventral views (M-P,S-T) at 24-30 hpf (C-L) and 36-50 hpf (M-T). Anterior to the left. krox20 (egr2b) or frb35 (egr2a) staining was used to identify rhombomere 5 (r5), which is strongly reduced in vhnf1hi2169 homozygous embryos. (A,B) In WT zebrafish embryos, vhnf1 is strongly expressed by 18s in the nephric duct (nd, arrows) and weakly in the gut endoderm (black arrowhead). hhex is expressed in the presumptive liver (Li) and pancreas (Pa) buds at 24 hpf (C). In vhnf1hi2169, hhex expression is lost (arrowheads in D) and prox1, which is normally exclusively expressed in the liver (E,M), is absent (arrowheads in F,N). gata6, gata4 and foxa3 are normally expressed in the gut endoderm, liver and pancreas at 24-30 hpf (G,I,K) and 48 hpf (O). In vhnf1hi2169, gata6 expression is lost (arrowheads in H), whereas gata4 (J) and foxa3 (L,P) expression is maintained in the gut endoderm. Expression of the liver-specific marker ceruloplasmin (cp) (Q) is totally abolished in mutants (R). Analyses of vhnf1 mutant transcripts show its expression in the nephric duct and in the mutant gut endoderm, but a complete absence of any endodermal budding (compare S with T).