Investigator Allan C. Spradling and his postdoctoral colleague Benjamin Ohlstein are at the Carnegie Institution of Washington, and they reported the finding in the February 16, 2007, issue of the journal Science

The stem cells know when the enteroendocrine cells turn over and when they need to make a replacement. If there are happy, healthy enteroendocrine cells nearby, they keep the stem cells from making more.

The research reveals the fine details of how stem cells replenish damaged or diseased tissues in a particular part of the body.

Unlike embryonic stem cells, which can become any kind of cell in the body, adult stem cells are usually limited to making one or a few types of cells that make up the tissue where they are found.

Basically, our bodies are constantly undergoing stem cell therapy [...] We would live one or two days without (adult) stem cells. It's essential to have these cells doing their thing.

According to researchers the adult stem cells found in a healthy region of tissue could be prompted to repopulate and repair diseased or damaged tissue nearby.

Spradling's research group first discovered intestinal stem cells in fruitflies in 2006.

He and Ohlstein had found that adult intestinal stem cells make two types of daughter cells:
- enterocytes, cells that line the intestine and absorb nutrients, and
- enteroendocrine cells, which belong to a family of hormone-secreting cells.

In the case of fruitflies — and very likely vertebrates such as humans — intestinal stem cells make the two types of cells according to cues they receive from other cells in their immediate environment. Those signals trip the switch of a key genetic pathway known as Notch that tells the cell what to become. Notch is a genetic regulatory pathway implicated in multiple differentiation processes.

In the current study, Spradling and Ohlstein were able to track the fate of the stem cells and their daughters by activating genetic markers in the intestinal stem cells of fruit flies and tracing their paths of development: "You can randomly turn on a marker in a cell and once the gene is on, it will be on in all of the progeny of that cell," said Spradling.

By tracking the cells in this way it became clear that the intestinal stem cells' differentiation into daughter cells was carefully controlled in response to the needs of the surrounding tissue.

By placing a molecule known as Delta on its own cell surface, the intestinal stem cells can switch on the Notch signaling pathway that turns a daughter cell into an enterocyte. When more hormone-producing cells are needed instead, the stem cells reduce the amount of Delta, and their daughters become enteroendocrine cells.

The fruitfly is a critical model for sorting out the mechanisms that control stem cell differentiation.

The same basic cellular and genetic processes are almost certainly at work in vertebrates, including humans.

More about Adult Stem Cells Decide the Fate of Their Daughters