Polyclonal structure of intestinal adenomas in ApcMin/+ mice with concomitant loss of Apc+ from all tumor lineages

Abstract

When tumors form in intestinal epithelia, it is important to know whether they involve single initiated somatic clones. Advanced carcinomas in humans and mice are known to be monoclonal. However, earlier stages of tumorigenesis may instead involve an interaction between cells that belong to separate somatic clones within the epithelium. The clonality of early tumors has been investigated in mice with an inherited predisposition to intestinal tumors. Analysis of Min (multiple intestinal neoplasia) mice chimeric for a ubiquitously expressed cell lineage marker revealed that normal intestinal crypts are monoclonal, but intestinal adenomas frequently have a polyclonal structure, presenting even when very small as single, focal adenomas composed of at least two somatic lineages. Furthermore, within these polyclonal adenomas, all tumor lineages frequently lose the wild-type Apc allele. These observations can be interpreted by several models for clonal interaction within the epithelium, ranging from passive fusion within regions of high neoplastic potential to a requirement for active clonal cooperation.

Figure 1

Whole-mount preparations, histological sections, and Apc immunohistochemistry of polyclonal intestinal adenomas. (A) Whole-mount preparation of the large intestine from chimera 113 after X-Gal staining, showing blue and white patches in the chimeric normal intestine and two adenomas, both of which contain both blue and white components. The arrow points to adenoma 5983, the arrowhead points to adenoma 5984 (see Table 2). (B) Histological section (5 μm) of adenoma 5983 stained with Apc antibody 3122. The box represents a region where blue and white regions join. (C) A ×4 magnification of the box in B showing a blue Apc-negative adenoma region on the right, a white Apc-negative adenoma region on the left, and normal Apc-positive crypts at the bottom (arrows). (D) Whole-mount preparation of the middle small intestinal region from chimera 113 after X-Gal staining; several white adenomas are present and one mixed blue/white adenoma, 6003, delineated by three arrows. (E) Histological section (5 μm) of adenoma 6003 stained with nuclear fast red. A blue adenoma region is observed on the left and a white adenoma region on the right. (F) A polyclonal microadenoma from the small intestine of chimera 113 stained with hematoxylin and eosin. (Scale bars = 2 mm for A and D, 0.5 mm for B and E, and 0.1 mm for F.)