Off Tangent Comix
| Proliferating Cells Can Evade microRNA Control |
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| Science - Biological Sciences | |||
| TS-Si News Service | |||
| Sunday, 17 August 2008 16:30 | |||
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Cambridge, MA, USA. New research findings have important implications for human cell types and tissues, including the brain, liver, and lung. While studying cell division, biologists discovered that proliferating cells can shift the output of their genes to evade regulation by microRNAs, the tiny molecules that normally regulate gene expression.
Stem cells have the capacity to divide for long periods of time even when most of the other cells are quiescent. A critical question for developmental biology is how they escape cell division stop signals. The new work extends accumulating evidence for this phenomenon and helps explain how some cells avoid regulatory controls during rapid division.
Proliferating cells express mRNAs with shortened 3' untranslated regions and fewer microRNA target sites. Rickard Sandberg, Joel R. Neilson, Arup Sarma, Phillip A. Sharp, Christopher B. Burge. Science 320, 1643-7.
The researchers studied T lymphocytes, a type of immune cell. Normal T cells start dividing rapidly when they encounter their target antigen (for example, a specific bacterium or virus). Their findings appear in Science. ![]() The research team was led by Chris Burge, associate professor of biology and biological engineering at MIT, in collaboration with the lab of Institute Professor Phillip Sharp. [N1-2]
Burge and his colleagues found that when T cells begin dividing, they start producing a shorter version of messenger RNA (mRNA), which carries protein-building instructions transcribed from DNA.
The shorter mRNA is missing about half of a section called the 3' untranslated region (UTR), which does not code for proteins, but contain binding sites for many microRNAs. When those binding sites are missing, the cell is able to escape control by the microRNAs, which generally function to suppress growth.
"When cells proliferate, they change their mRNA in a way that reduces the impact of microRNA regulation," Burge explained. For normal T cells, that response is desirable; however, in cancerous cells it may not be.
Since microRNAs were identified in mammals several years ago, much work has been done on how over- or underexpression of microRNA affects cell proliferation. There have been significant observations of the same effect in many other human cell types and tissues. The most notable types are those for the brain, liver, and lung. Work continues to determine whether this is a predominant or even ubiquitous pattern in human developmental biology.
Learning more about how mRNAs evade microRNA control could help researchers develop ways to control the mRNA switch from the long form to the short form, so the mRNA remains susceptible to microRNA control, Burge said.
The findings could also aid design of small RNA therapeutics, by focusing on targeting those UTR regions that remain unchanged when cells proliferate.
The Christopher Burge Laboratory uses computational and experimental approaches to study mechanisms of gene expression and regulation, developing algorithms for gene identification and other genomic applications.
Burge says "A unifying goal of our research is to understand the rules of RNA splicing specificity: how the precise locations of introns and splice sites are identified in primary transcripts."
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| Last Updated on Monday, 18 August 2008 01:35 |










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