The Intestinal Stem Cell Niche
The intestine is one of the most rapidly proliferating tissues in the human body and serves as an important model to understand tissue stem cell function and homeostasis. The absorptive function of the intestine is served by the epithelium lining the villi, composed of differentiated cell types, which are replenished by the proliferative crypts that contain the intestinal stem cells. The concept of the intestinal stem cell niche was proposed almost 40 years ago and two different models of the intestinal stem cell location have since been developed. The characterization of genetic markers has allowed the identification of different stem cell populations in the intestinal epithelium and provided data supporting both these models. Recent studies of the behavior and interaction of intestinal stem cells have also revealed an important role of the intestinal stroma in maintaining the stem cells. More thorough characterization of the intestinal stem cell niche has allowed for the development of sophisticated methodologies to culture intestinal crypts ex vivo. Here we review various models of the intestinal stem cell populations and the interactions between them. The anatomical components and signaling pathways supporting the stem cell niche will also be described.
