The intestinal epithelium constitutes a system of constant and rapid renewal triggered by proliferation of intestinal stem cells (ISCs), and is an ideal system for studying cell proliferation, migration, and differentiation. Primary cell cultures have proven to be promising for unraveling the mechanisms involved in epithelium homeostasis. In 2009, Sato et al. established a long‐term primary culture to generate epithelial organoids (enteroids) with crypt‐ and villus‐like epithelial domains representing the complete census of progenitors and differentiated cells. Similarly, isolated ISCs expressing Lgr5 (leucine‐rich repeat‐containing G protein–coupled receptor) can generate enteroids. Here, we describe methods to establish gastric, small intestinal, and colonic epithelial organoids and generate Lgr5^+ve single cell–derived epithelial organoids. We also describe the imaging techniques used to characterize those organoids. This in vitro model constitutes a powerful tool for studying stem cell biology and intestinal epithelial cell physiology throughout the digestive tract. Curr. Protoc. Mouse Biol. 3:217‐240 © 2013 by John Wiley & Sons, Inc.

Although intestinal homeostasis is maintained by intestinal stem cells (ISCs), regeneration is impaired upon aging. Here, we first uncover changes in intestinal architecture, cell number, and cell composition upon aging. Second, we identify a decline in the regenerative capacity of ISCs upon aging because of a decline in canonical Wnt signaling in ISCs. Changes in expression of Wnts are found in stem cells themselves and in their niche, including Paneth cells and mesenchyme. Third, reactivating canonical Wnt signaling enhances the function of both murine and human ISCs and, thus, ameliorates aging-associated phenotypes of ISCs in an organoid assay. Our data demonstrate a role for impaired Wnt signaling in physiological aging of ISCs and further identify potential therapeutic avenues to improve ISC regenerative potential upon aging.

Human intestinal organoids (HIOs) are a tissue culture model in which small intestine-like tissue is generated from pluripotent stem cells. By carrying out unsupervised hierarchical clustering of RNA-sequencing data, we demonstrate that HIOs most closely resemble human fetal intestine. We observed that genes involved in digestive tract development are enriched in both fetal intestine and HIOs compared to adult tissue, whereas genes related to digestive function and Paneth cell host defense are expressed at higher levels in adult intestine. Our study also revealed that the intestinal stem cell marker OLFM4 is expressed at very low levels in fetal intestine and in HIOs, but is robust in adult crypts. We validated our findings using in vivo transplantation to show that HIOs become more adult-like after transplantation. Our study emphasizes important maturation events that occur in the intestine during human development and demonstrates that HIOs can be used to model fetal-to-adult maturation.