Abstract 2717: The clonal architecture of tumors in the mammalian intestines.
Authors: Zahm Christopher D. , Szulczewski Joseph , Paul Olson Terrah J. , Nettekoven Laura , Leystra Alyssa , Albrecht Dawn M. , Clipson Linda , Eliceiri Kevin W. , Newton Micheal A. , Halberg RIchard B. 
Published: August 2014

Abstract
Background
Evidence is steadily accumulating that tumors can have a polyclonal origin. In fact, a recent review finds that there is evidence for polyclonal origin in at least 24 different human tumors types. Insights into clonality of intestinal tumors have been achieved through the generation of aggregation chimeras from early-stage mouse embryos and statistical analysis combining information about the pattern of chimerism with tumor phenotype. However, this experimental approach is incredibly laborious and very expensive.
Methods
To overcome these significant limitations, we developed a mosaic mouse model that expresses fluorescent proteins (FPs) in a variegated pattern throughout the distal small bowel and colon and have used this model to investigate the clonal origin of intestinal tumors. Briefly, our model is based on the mosaic expression of Cre recombinase in the intestinal epithelium and it can be generated by simple crosses, eliminating the time and cost associated with generating aggregation chimeras. In addition, FPs allow us to use advanced in and ex vivo imaging techniques such as dual-photon excitation microscopy and fluorescent endoscopy to address fundamental questions.
Experimental Design
Mosaic mice carrying the Min allele of Apc are predisposed to developing tumors throughout the intestinal tract. Many of the tumors (41%) from the distal small bowel and colon contained both green and red neoplastic cells confirming that mosaic mice can be used to detect polyclonal architecture. Dual-photon excitation microscopy was performed on whole tumors that had been optically cleared revealing the sub-surface structure of the epithelium and tumors to a depth of ∼350 μM. This detailed analysis revealed that some tumors can be derived from as many as 4 progenitors.
Mosaic mice were also treated with azoxymethane (AOM) and AOM in the presence the inflammatory agent dextran sodium sulphate (DSS). The length of exposure to DSS was varied across groups to determine the effects of chronic versus acute inflammation. Results demonstrated that the effect of chronic inflammation is subtle, whereas acute inflammation has a significant effect on clonal architecture of the tumors. One possible explanation for these results is that chronic inflammation supplants the need for interactions among different progenitors to establish a tumor, whereas acute inflammation enhances clonal interactions.
Conclusion
Together these data demonstrate that mosaic mice are useful for studying the clonal origin of tumors. We also find evidence that polyclonal architecture is important in multiple biological contexts within the mammalian intestine. Because FP expression is ubiquitous the same approach can be used to study clonal origin of tumors in any tissue in which mosaic Cre expression can be induced. Having a better understand of the complexity of tumor origin could profoundly change our strategies for the prevention and treatment of cancers.
Citation Format: Christopher D. Zahm, Joseph Szulczewski, Terrah J. Paul Olson, Laura Nettekoven, Alyssa Leystra, Dawn M. Albrecht, Linda Clipson, Kevin W. Eliceiri, Micheal A. Newton, RIchard B. Halberg. The clonal architecture of tumors in the mammalian intestines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2717. doi:10.1158/1538-7445.AM2013-2717