Fig. 2. Defect in the gut of Del(1-10) mutants. Whole-mount RNA in situ hybridization analysis of gene expression in dissected posterior midgut of E12 mouse embryos. Hoxd11 (A-C), Hoxd12 (D-F), Hoxd13 (G-I) Hoxa10 (J-L), Hoxa6 (M-O) and Fgf10 (P-R). Caecum budding is well underway in wild-type controls (A,D,G,J,M,P), perceptibly delayed in heterozygotes (B,E,H,K,N,Q) and is absent from homozygous specimens (C,F,I,L,O,R). In heterozygous specimens, ectopic Hoxd11 and Hoxd12 expression is detected in the anterior part and in the entire caecum bud, respectively (B,E). In homozygotes, Hoxd11 and Hoxd12 expression is detectable in the presumptive area for caecum budding (asterisks in C,F). In all three genotypes, including homozygous embryos, the demarcation between Hoxa10-negative and Hoxa10-positive regions seems to be rather faithfully maintained (J-L). Retarded bud growth in heterozygous specimens is correlated with reduced hybridisation signals for Hoxa6 (N) and Fgf10 (Q). Absence of bud growth correlates with the massive reduction of the expression domain of both these genes, leaving only of a tiny expression domain for both Hoxa6 (O) and Fgf10 (R).