GO IN DEPTH

Gut Stem Cells

Gut Stem Cells Queensland Fruit Fly - Bactrocera tryoni
Photo Credit: By James Niland [CC-BY-2.0], via Wikimedia Commons

Overfeeding fruit flies sets off a chain reaction that makes their intestines grow.


Transcript

How to grow a gut. I’m Bob Hirshon and this is Science Update.

When we eat a lot, our digestive systems actually get bigger. Now, researchers at the University of California at Berkeley may have found out why. Biologist David Bilder and his colleagues studied fruit flies. When fed, the flies’ gut cells make their own insulin, which activates nearby stem cells. 

Bilder:
So the local insulin is immediately upregulated upon feeding. And it both increases the division rates of the stem cells, and also makes it more likely that they will produce new stem cells.

Having extra stem cells, in turn, makes it possible to grow the gut rather than just maintain it. In the Berkeley experiment, led by Bilder and postdoc Lucy O’Brien, the flies’ guts grew up to four times bigger in as many days. The findings could  lead to better treatments for obesity, and for rebuilding intestinal tissue lost to disease or injury. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

It's well known that gaining weight can create a damaging cycle: the more weight you gain, the more calories your body demands, and the more you eat—resulting in even more weight gain. This study suggests that it's not just extra fat that may drive people to keep overeating. The gut itself—specifically, the intestine—may actually grow longer and bigger, increasing its capacity to absorb food and pack on the pounds.

This study looked at fruit fly guts, which function in similar ways to human intestines, except they're a lot smaller and simpler. The key targets of the study are stem cells in the intestines. Stem cells are a kind of all-purpose cell that can transform into more specific cells under certain conditions. Embryonic stem cells, for example, create all the different body parts in a human fetus. Adult stem cells have been assumed not to work quite that hard. Researchers believed that the stem cells in an adult intestine, for example, activate only to replace lost or damaged intestinal cells as needed.

Bilder and O'Brien's study suggests they can do a lot more than that. Like human intestines, fruit fly intestines can produce insulin, a hormone that regulates sugar metabolism. When the fly eats, the cells release insulin, and the more it eats, the more insulin it produces. This study found that insulin triggers nearby intestinal stem cells to start making new cells—not replacement cells, but additional cells that expand the size of the gut. Not only that, the stem cells also make more new stem cells than usual, resulting in a greater capacity to make even more intestinal cells.

In this study, the fruit fly gut grew to four times its original size in just four days of overfeeding. When the feeding was reduced, the gut shrank again. But in people, constant overeating may keep our intestines super-sized for a long period of time, and that in turn may drive us to eat more. The findings are consistent with observations that hibernating animals' intestines shrink to as little as one-third their normal size during their winter sleep. Future studies will try to confirm if human intestines grow and shrink this dramatically, and whether changes in eating habits or medical interventions can counteract that effect.

Now try and answer these questions:

  1. What happened to the fruit flies' intestines when they overate?
  2. Describe the chain of events, starting with the introduction of food, and ending with a larger gut.
  3. Why might this be significant in understanding human obesity?
  4. Might this study help explain why dieting can be so difficult, especially in the beginning?  Why or why not?

You may want to check out the Science Update, Tissue Regeneration to learn more about how researchers use stem cells.

Obesity: The Science Inside is an online booklet that discusses the importance of good health habits such as eating right and exercising. It talks about how the body takes in energy and what it does with excess energy it doesn't use up.


Going Further


For Educators

Learn more about how researchers use stem cells in the Science Update lesson Tissue Regeneration.

Obesity: The Science Inside is an online booklet that discusses the importance of good health habits such as eating right and exercising. It talks about how the body takes in energy and what it does with excess energy it doesn't use up.


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