Tales from the crypt

How many stem cells reside in a human colonic crypt and how do they divide and regenerate? According to the deterministic theory, a small number of “immortal” stem cells haunt a crypt, and when they divide, each generates a single replacement stem cell. The stochastic model, in contrast, contends that a crypt niche harbors many stem cells, and each cell division randomly generates one, two, or no new stem cells. In this model, stem cell lines may be lost over time, and “bottlenecks” will eventually develop in which all stem cells in a niche will diverge from a recent, common ancestor.

A new and clever strategy for studying stem cell dynamics, devised by Darryl Shibata and colleagues (University of Southern California, Los Angeles, CA), uses DNA methylation tags as markers...