Polyclonality of familial murine adenomas: Analyses of mouse chimeras with low tumor multiplicity suggest short-range interactions

Abstract

In previous studies demonstrating the polyclonal structure of familial intestinal adenomas, high tumor multiplicity made it difficult to eliminate the possibility that polyclonality arose by the random collision of distinct initiated clones as opposed to some form of clonal interaction. We sought to test further the random collision hypothesis. Chimeric mice carrying the multiple intestinal neoplasia (Min) mutation of the adenomatous polyposis coli gene (Apc) and homozygous for the tumor resistance allele of the Mom1 locus were established. These chimeras also display a strong propensity for tumors of polyclonal structure, despite their markedly reduced tumor multiplicity. Considering tumor sizes and multiplicities, the observed fraction of overtly polyclonal heterotypic adenomas was significantly higher than predicted by the random collision hypothesis. This finding supports models of polyclonality involving interaction among multiple initiated clones. The extent of clonal interaction was assessed by statistical analyses that relate the observed frequency of overtly polyclonal heterotypic tumors to the geometry of the chimeric patches and the pattern of underlying crypts. These statistical calculations indicate that the familial adenomas of the Apc Min/؉ mouse may commonly form through interactions between clones as close as 1-2 crypt diameters apart.Bayesian image reconstruction ͉ clonal interactions ͉ colon cancer ͉ spatial statistics ͉ tumorigenesis M ost current models of tumorigenesis involve a monoclonal origin. The evidence for monoclonality at the earliest stages of spontaneous intestinal neoplasia is limited. Intestinal adenomas and carcinomas in carcinogen-treated mice (1, 2) and large adenomas in humans (3) seem to be monoclonal. The clonality of normal and neoplastic tissue is assessed by the analysis of patches in chimeras or mosaics heterotypic for a clonal lineage marker. The ability to detect polyclonality in early human tumors is restricted by the large patch sizes of X-inactivation mosaics (4). The first indication that familial intestinal adenomas were commonly polyclonal in structure came from a study of a mosaic XY 7 XO male patient with familial adenomatous polyposis (5). In that study, 5% of microadenomas were found to have a mixed karyotype, which led the authors to suggest that as many as 76% are polyclonal (ref. was compromised by high tumor multiplicity. In the latter case, it was estimated that a model of passive clonal interaction could explain the overall frequency of heterotypic adenomas if the intestinal epithelium is heterogeneous with only a portion of the tissue susceptible to tumorigenesis. Regional heterogeneity could involve exposure to dietary carcinogens. Indeed, recent studies have found that adenomas in B6 Min mice form predominantly in the distal segment of the small intestine (9). We have therefore assessed the incidence of heterotypic tumors in chimeric Min mice in which the tumor multiplicity has been strongly reduced by homozygosity for the resistance allele of the...

Suppression of Intestinal Neoplasia by Deletion of Dnmt3b

“…It has been suggested, based on the analysis of chimeric Apc Min/ϩ mice, that tumors in the small intestine arise by active interactions between crypts promoting loss of Apc and thus resulting in the formation of polyclonal adenomas (36). In that study, however, only 22% of all tumors were identified as polyclonal.…”

“…Since Cre-mediated recombination is irreversible and the majority of tumors in Apc Min/ϩ mice are considered to be monoclonal (22,27,36), this suggests that Dnmt3b deletion occurred after tumor initiation during tumor growth. Two observations are consistent with this idea.…”

Monoallelic silencing and haploinsufficiency in early murine intestinal neoplasms

“…This finding may reflect the increased level of normal epithelial and stromal admixture in the nonpedunculate mouse tumors that are dissected from the small intestine. Alternatively, this broad distribution of allelic ratios may reflect the known polyclonality of Min tumors (21) or differences between tumors of the small intestine and the colon. By contrast, the high concordance between the majority of gLOH vs. cLOH allelic ratios in F1-Pirc tumors and between the gMOH vs. cMOH allelic ratios in normal epithelium indicates that these pedunculate colonic rat tumors are dissected with less admixture of normal epithelial and stromal tissue, resulting in more highly defined LOH and MOH classes.…”

“…The F1-Pirc rat provides a large proportion of colon tumors that are highly enriched for epithelial tumor material. The residual level of admixture between LOH and MOH classes may be owing to the nonmedullary nature of all intestinal tumors, or it may reflect polyclonality as documented in the mouse and human (21,22,34).…”

“…These tumors show a greater gMOH/cLOH contribution admixed with both gMOH/cMOH and gLOH/cLOH classes. Thus, admixture between LOH and MOH components is observed in adenomas of both the Rb9-Min mouse and F1-Pirc rat and may reflect the polyclonal nature of early intestinal cancer (21,22). A full statistical analysis of admixture is presented in SI Materials and Methods and Fig.…”