Fig. 3. Role of Hoxd12 in caecum agenesis. (A) Derivation of the Del(4-11) allele by TAMERE. (B-J) Whole-mount RNA in situ hybridization of Hoxd12 (B-D), Fgf10 (E-G) and Pitx1 (H-J) transcripts in wild-type control (B,E,H), Del(4-11)-deficient HoxD cluster mutant heterozygous (C,F,I) and homozygous (D,G,J) posterior midguts at E12.5. In wild-type controls, the Hoxd12 transcript is always absent from the caecum bud (B), whereas localized expression of both Fgf10 (E) and Pitx1 (H) are always detectable. Caecum bud growth is conspicuously retarded in Del(4-11) heterozygous specimens and is correlated with robust Hoxd12 transcript accumulation (C), reduced hybridization signals for Fgf10 (F) and undetectable signal for Pitx1 (I) in bud mesenchyme. Absence of bud growth in homozygous specimens is correlated with extremely reduced of Fgf10 (asterisk in G) and complete absence of localized Pitx1 (J).