The mammalian intestine is covered by a single layer of epithelial cells that is renewed every 4-5 days. This high cell turnover makes it a very attractive and comprehensive adult organ system for the study of cell proliferation and differentiation. The intestine is composed of proliferative crypts, which contain intestinal stem cells, and villi, which contain differentiated specialized cell types. Through the recent identification of Lgr5, an intestinal stem cell marker, it is now possible to visualize stem cells and study their behavior and differentiation in a much broader context. In this review we describe the identification of intestinal stem cells. We also discuss genetic studies that have helped to elucidate those signals important for progenitor cells to differentiate into one of the specialized intestinal epithelial cell types. These studies describe a genetic hierarchy responsible for cell fate commitment in normal gut physiology. Where relevant we also mention aberrant deregulation of these molecular pathways that results in colon cancer.

Stem cells, self-renewal, and differentiation in the intestinal epithelium.

Transcription factor achaete scute-like 2 controls intestinal stem cell fate.

(1990). A Comprehensive Study of the Radiobiological Response of the Murine (BDF1) Small Intestine. International Journal of Radiation Biology: Vol. 58, No. 6, pp. 925-973.

A comprehensive study of the radiobiological response of the murine (BDF1) small intestine.

Transformations from one tissue type to another make up a well established set of phenomena that can be explained by the principles of developmental biology. Although these phenomena might be rare in nature, we can now imagine the possibility of deliberately reprogramming cells from one tissue type to another by manipulating the expression of transcription factors. This approach could generate new therapies for many human diseases.

Metaplasia and transdifferentiation: from pure biology to the clinic.

https://www.gastrojournal.org/article/S0016-5085(77)80156-X/pdf

Compensation by the Residual Intestine After Intestinal Resection in the Rat: I. Influence of amount of tissue removed

Following 1600 R of X-rays there was a reduction in the number of crypts in the small intestine of the mouse by 77% as measured 5 days later. However, by 21 days the number had increased steadily to levels approaching normal. The number of villi did not change following irradiation. The mechanism of increase in crypt number was by budding and fission of repopulated crypts which had become larger than normal. Some aspects of crypt organization are discussed.

B. H. Millen

Papers

Fission of crypts in the small intestine of the irradiated mouse