Intestinal polyposis, a precancerous neoplasia, results primarily from an abnormal increase in the number of crypts, which contain intestinal stem cells (ISCs). In mice, widespread deletion of the tumor suppressor Phosphatase and tensin homolog (PTEN) generates hamartomatous intestinal polyps with epithelial and stromal involvement. Using this model, we have established the relationship between stem cells and polyp and tumor formation. PTEN helps govern the proliferation rate and number of ISCs and loss of PTEN results in an excess of ISCs. In PTENdeficient mice, excess ISCs initiate de novo crypt formation and crypt fission, recapitulating crypt production in fetal and neonatal intestine. The PTEN-Akt pathway probably governs stem cell activation by helping control nuclear localization of the Wnt pathway effector β-catenin. Akt phosphorylates β-catenin at Ser552, resulting in a nuclear-localized form in ISCs. Our observations show that intestinal polyposis is initiated by PTEN-deficient ISCs that undergo excessive proliferation driven by Akt activation and nuclear localization of β-catenin. Accession codes. Gene Expression Omnibus (GEO): GSE6078.URLs. GEO: http://www.ncbi.nlm.nih.gov/projects/geo/.Supplementary information is available on the Nature Genetics website. COMPETING INTERESTS STATEMENTThe authors declare that they have no competing financial interests. HHS Public AccessAuthor manuscript Nat Genet. Author manuscript; available in PMC 2015 December 16. Published in final edited form as:Nat Genet. 2007 February ; 39(2): 189-198. doi:10.1038/ng1928. Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptThe failure of most current therapies to cure cancer has led to the hypothesis that treatments targeted at malignant proliferation spare a more slowly cycling 'cancer stem cell' population that has the ability to regenerate the tumor 1 . Recently, cancer stem cells have been identified and shown to seed tumors upon transplantation into a secondary host [2][3][4] . However, little is known about the process by which mutation(s) in a stem cell result in primary tumor initiation.Although there are many 'causes' of intestinal cancer, it is well established that almost all cases begin with the development of benign polyps, mainly involving benign neoplastic proliferation of epithelium. The epithelium of the small intestine is composed of a proliferation compartment (crypt) and a differentiation compartment in the villus (Fig. 1a). ISCs, located near the crypt base and above Paneth cells 5,6 , give rise to enterocytes, goblet cells, enteroendocrine cells and Paneth cells [6][7][8] . Intestinal polyposis features a substantial increase in the number of crypts (crypt expansion) and a reduction in epithelial cell differentiation 6,7,9,10 . A key question 7,9,11 is whether stem cells are involved in the abnormal crypt expansion during polyp initiation.Studies of human hereditary intestinal polyposis syndromes (which typically, but not uniformly, predispose affected individuals to gastrointes...

Osteoblasts expressing the homophilic adhesion molecule N-cadherin form a hematopoietic stem cell (HSC) niche. Therefore, we examined how N-cadherin expression in HSCs relates to their function. We found that bone marrow (BM) cells highly expressing N-cadherin (N-cadherin(hi)) are not stem cells, being largely devoid of a Lineage(-)Sca1(+)cKit(+) population and unable to reconstitute hematopoietic lineages in irradiated recipient mice. Instead, long-term HSCs form distinct populations expressing N-cadherin at intermediate (N-cadherin(int)) or low (N-cadherin(lo)) levels. The minority N-cadherin(lo) population can robustly reconstitute the hematopoietic system, express genes that may prime them to mobilize, and predominate among HSCs mobilized from BM to spleen. The larger N-cadherin(int) population performs poorly in reconstitution assays when freshly isolated but improves in response to overnight in vitro culture. Their expression profile and lower cell-cycle entry rate suggest N-cadherin(int) cells are being held in reserve. Thus, differential N-cadherin expression reflects functional distinctions between two HSC subpopulations.

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The embryonic pancreas is thought to develop from pluripotent endodermal cells that give rise to endocrine and exocrine cells. A key guidance mechanism for pancreatic development has previously been found to be epithelial-mesenchymal interaction. Interactions within the epithelium, however, have not been well studied. Glucagon is the earliest peptide hormone present at appreciable levels in the developing pancreatic epithelium (embryonic day [E]-9.5 in mouse). Insulin accumulation begins slightly later (E11 in mouse), followed by a rapid accumulation during the "second wave" of insulin differentiation ( approximately E15). Here we found that blocking early expression and function of glucagon, but not GLP-1, an alternate gene product of preproglucagon mRNA, prevented insulin-positive differentiation in early embryonic (E11) pancreas. These results suggest a novel concept and a key role for glucagon in the paracrine induction of differentiation of other pancreatic components in the early embryonic pancreas.