( Everyone knows that stem cells are cont...)Discovery suggests why stem cells run through stop signs

Everyone knows that stem cells are controversial. Many people know that stem cells can grow into virtually any cell type found in the body, from a red blood cell to a muscle cell to a brain cell. But no one really knows why stem cells continue to divide and renew themselves long after the point where other cells stop dividing.

Now scientists at Northwestern University and the University of Washington offer one of the first clues as to why stem cells ignore stop signs in the cell cycle: a special molecular mechanism has cut the brakes. The researchers found that tiny bits of genetic material called microRNAs are necessary for stem cell division to take place, suggesting that microRNAs shut off the signals that stop cell division in most other cells.

The findings were published online this week by the journal Nature. In the paper, the researchers also speculate that microRNAs may play a similar role in cancer cells, encouraging their proliferation. This speculation is supported by three other new papers published this week in Nature linking microRNAs to cancer.

According to authors Richard Carthew, Owen L. Coon Professor of Molecular Biology at Northwestern University, and Hannele Ruohola-Baker, professor of biochemistry at the University of Washington, microRNAs can regulate gene expression and give stem cells a green light to pass from the normal stop phase to the stage in which they begin replicating their DNA for later division.

In their work, Carthew and Ruohola-Baker focused on fruit flies, which have approximately 80 types of microRNAs. They genetically modified stem cells from the fruit flies' ovaries and studied how many egg chambers the mutant stem cells produced as compared to normal stem cells. The production rate in the mutant cells fell over the course of 12 days, and the researchers concluded it was because the mutant stem cells were no longer dividing.

Without the microRNAs at work, the brakes were applied to the
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Source:Northwestern University

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