Red blood cells regenerate every four months but the lining of the intestine regenerates itself every few days. The cells that help humans absorb food are constantly being produced and the various cell types that do this come from stem cells that reside deep in the inner recesses of the accordion-like folds of the intestines, called villi and crypts. 

Like ancient burial crypts, these adult stem cells are something of a mystery. Two types of intestinal stem cells have been proposed to exist but the relationship between them has been unclear. One type of stem cell divides slowly and resides at the sides of intestinal crypts. The other divides much more quickly and resides at the bottom of the crypts.

Some researchers have been proponents of one type of stem cell or the other as the 'true' intestinal stem cell and recent may reconcile this controversy. New findings in Science suggest that these two types of stem cells are related. In fact, each can produce the other.

A stem cell (blue) from the intestinal crypt. Credit: Norifumi Takeda, Raj Jain and Jon Epstein, Perelman School of Medicine, University of Pennsylvania

The discovery that rapidly cycling gut stem cells can regenerate the quiescent stem cells -- slowly dividing and probably long-lived -- suggests that the developmental pathways in human organs that regenerate quickly like in the gut, skin, blood, and bone, may be more flexible than previously appreciated.

"We actually began our studies by looking at stem cells in the heart and other organs," says Jonathan Epstein, MD, chairman of the Department of Cell and Developmental Biology at the University of Pennsylvania. "In other tissues in the body, slowly dividing cells can sometimes give rise to more rapidly dividing stem cells that are called to action when tissue regeneration is required. Our finding that this can happen in reverse in the intestine was not expected.

"This better appreciation and understanding may help us learn how to promote the regeneration of tissue-specific adult stem cells that could subsequently help with tissue regeneration. It may also help us to understand the cell types that give rise to cancer in the colon and stomach."

Citation: Norifumi Takeda, Rajan Jain, Matthew R. LeBoeuf, Qiaohong Wang, Min Min Lu, and Jonathan A. Epstein, 'Interconversion Between Intestinal Stem Cell Populations in Distinct Niches', Science Published online 10 November 2011 DOI:10.1126/science.1213214