Fig. 4. `Anterior' Hoxd genes promote adult caecum size in mice. (A-I) Dissected ileo-caecal transition zones of three genotypes, illustrating key examples of the phenotypic series presented in Table 1. A,A',D,G depict X-Gal-stained newborn specimens, to confirm the identity of the complementing alleles. Arrowheads in A,A',D point to the anterior limit of Hoxd11/lac marker gene expression in mesenchyme, associated with the respective alleles, depicted in the line diagrams on the right. In gut mesenchyme, del(8i-13) shows a more anterior Hoxd11/lac expression involving the posterior ileum (A,A'), while the reporter gene associated with the del(11-13) allele is limited at the ileo-caecal junction, reminiscent of endogenous Hoxd11. Blue staining in G is due to endogenous activity in enterocytes, which does not involve the gut mesenchyme. The lac fusion protein does not have Hoxd11 function, consistent with lack of caecum growth promotion by the del(8i-13) allele (A,A',B) in the presence of ectopic Hoxd12. By contrast, in the case of del(11-13), the presence of the caecum (D,E) indicates growth promotion by Hoxd8, Hoxd9 and Hoxd10 present in addition to the Hoxd1, Hoxd3 and Hoxd4 loci, which alone were not sufficient to neutralize ectopic Hoxd12. Control guts are shown in G and H for comparison.