Reprogramming of intestinal differentiation and intercalary regeneration in Cdx2 mutant mice

Abstract

The homeobox gene Cdx2, a homologue of the Drosophila gene caudal, has been implicated in the control of cell differentiation in the intestinal epithelium. Recently, we showed that mice in which one allele of the Cdx2 gene had been inactivated by homologous recombination developed multiple intestinal polyp-like lesions that did not express Cdx2 and that contained areas of squamous metaplasia in the form of keratinizing stratified squamous epithelium, similar to that occurring in the mouse esophagus and forestomach. We have now examined colonic lesions from 98 Cdx2+/- mice and report that the lesions are composed of heterotopic stomach and small intestinal mucosa. We conclude that Cdx2 directs endodermal differentiation toward a caudal phenotype and that haploinsufficient levels of expression in the developing distal intestine lead to homeotic transformation to a more rostral endodermal phenotype, such as forestomach epithelium that does not express Cdx2 during normal development. Intercalary growth (epimorphic regeneration), which previously has never been described in mammals, then occurs, resulting in the ordered "filling in" of tissue types at the discontinuity between the gastric and colonic epithelia. This intercalary growth in a restricted space results in the formation of the polypoid lesions observed.

Figure 1

The frequency of polyps in 98 mice plotted against their age. The numbers of animals at each monthly time point are indicated in brackets. The slope of the line is not significantly different from zero (P = 0.92).

Figure 2

Portion of a colonic polyp from a Cdx2+/− mouse showing the sequence SSE, gastric cardia (GCa) containing columnar mucus-secreting cells with basal nuclei, and gastric corpus (GCo) containing clearly identifiable parietal (oxyntic) cells (arrows). (Bar = 45 μm.)

Figure 3

Montage showing the lateral edge of a colonic polyp in a Cdx2+/− mouse. (Top) The sequence—gastric corpus (GCo), gastric antrum (GA), small intestine (SI), and colon (C)—is clearly seen. (Bar = 130 μm.) (A) Transition from GCo to GA. Parietal (oxyntic) cells (closed arrow heads) and enterochromaffin-like cells (arrows) are easily identifiable, as are the columnar mucus-secreting cells of the gastric antrum (open arrow heads). (Bar = 55 μm.) (B) Transition from GA to SI. Goblet cells in the villi and Paneth cells (arrow) situated in the crypts are clearly seen adjacent to the branched mucus-secreting cells of the gastric antrum. (Bar = 55 μm.) (C) Transition from SI to C. Stunted villi with goblet cells and Paneth cells (arrow) in the crypts between villi, lie adjacent to colonic tissue. (Bar = 55 μm.) (D) Portion of B magnified further to show Paneth cells with characteristic eosinophilic granules. (Bar = 20 μm.)

Figure 4

Portion of a colonic polyp showing the junction of gastric cardia (GCa) and gastric corpus (GCo). (Upper) This section is stained with hematoxylin and eosin. (Lower) An adjacent section was incubated with antiserum to the gastric proton pump to locate oxyntic cells in the gastric corpus. (Bars = 55 μm.)

Figure 5

This section of a colonic polyp shows characteristics of gastric antrum (GA) and normal colon (C) distal to it. The section was stained by Mowry’s technique (13) to show PAS-staining (neutral) mucopolysaccharides in the polyp (upper portion of section) and alcian-blue-staining (acid) mucopolysaccharides in the normal colon (lower portion of section). (Bar = 50 μm.)

Figure 6

A section adjacent to Fig. 5 was stained for TFF2. The heterotopic tissue with the histological phenotype of gastric antrum (upper portion of section) stains strongly, whereas the phenotypically normal colonic-type mucosa is negative (lower portion of section). (Bar = 50 μm.)

Figure 7

Ectopic SSE in the small intestine of a 5-day-old Cdx2+/− mouse. The large endosomal vacuoles in the villous enterocytes (arrow) are typical of the small intestine before weaning. (Bar = 80 μm.)

Figure 8

Polyp-like lesion in the proximal colon of a Cdx2+/− mouse. The cells in the main part of the lesion stain negatively with Cdx2 antibody and are typical of the mucous glands of pyloric antrum. The intercalated small intestinal-type mucosa at the edge of the lesion, however, stains positive for Cdx2 (arrowhead). (Bar = 100 μm.)