Written by Lucy Erin O’Brien
Most cells in your body are in a constant state of turnover. The cells of your lungs, for instance, replace themselves every 2 to 3 weeks and, believe it or not, you get a new intestine every 2 to 3 days. We can thank adult stem cells residing in these organs for producing the new replacement cells. But with this continual flux, how do the stem cells manage to generate just the right number of cells to maintain the same organ size? Just a slight imbalance would lead to either too few cells or too many which can lead to organ dysfunction and disease.
The intestine turnovers every five days. Stem cells (green) in the fruit fly intestine maintain organ size and structure.
Image: Lucy Erin O’Brien/Stanford U.
Stanford University researchers published results on Friday in Nature that make inroads into explaining this fascinating, fundamental question about stem cell and developmental biology. Studying the cell turnover process of the intestine in fruit flies, the scientists discovered that, as if speaking its final words, a dying intestinal cell, or enterocyte, directly communicates with an intestinal stem cell to trigger it to divide and provide young, healthy enterocytes.
To reach this conclusion, the team first analyzed young enterocytes and showed that a protein these cells produce, called E-cadherin, blocks the release of a growth factor called EGF, a known stimulator of cell division. When young enterocytes became old and begin a process called programmed cell death, or apoptosis, the E-cadherin levels drop which removes the inhibition of EGF. As a result, a nearby stem cell now receives the EGF’s cell division signal, triggering it to divide and replace the dying cell. In her summary of this research in Stanford’s Scope blog, science writer Krista Conger explains how the dying cell’s signal to a stem cell ensures that there no net gain or loss of intestinal cells:
“The signal emitted by the dying cell travels only a short distance to activate only nearby stem cells. This prevents an across-the-board response by multiple stem cells that could result in an unwanted increase in the number of newly generated replacement cells.”
Because E-cadherin and the EGF receptor (EGFR) are each associated with certain cancers, senior author Lucy Erin O’Brien ponders the idea that her lab’s new findings may explain an underlying mechanism of tumor growth:
“Intriguingly, E-cadherin and EGFR are each individually implicated in particular cancers. Could they actually be cooperating to promote tumor development through some dysfunctional version of the normal renewal mechanism that we’ve uncovered?”
Quote: Lucy Erin O’Brien – O’Brien/Stanford U.
REF: The Stem Cellar. (2017). Stories that caught our eye last week. [online] Available at: https://blog.cirm.ca.gov/2017/09/05/stories-that-caught-our-eye-last-week-dying-cells-trigger-stem-cells-crispr-videogames-and-an-obesity-stem-cell-link/ [Accessed 15 Sep. 2017].
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