( Johns Hopkins Kimmel Cancer Center scie...)Master Switches Found for Adult Blood Stem Cells,Health

Johns Hopkins Kimmel Cancer Center scientists have found a set of "master switches" that keep adult blood-forming stem cells in their primitive state//. Unlocking the switches' code may one day enable scientists to grow new blood cells for transplant into patients with cancer and other bone marrow disorders.

The scientists located the control switches not at the gene level, but farther down the protein production line in more recently discovered forms of ribonucleic acid, or RNA. MicroRNA molecules, once thought to be cellular junk, are now known to switch off activity of the larger RNA strands which allow assembly of the proteins that let cells grow and function.

"Stem cells are poised to make proteins essential for maturing into blood cells, but microRNAs keep them locked in their place," says cancer researcher Curt Civin, M.D., Ph.D., who led the study. The journal account will appear online the week of February 5 in the early edition of the Proceedings of the National Academy of Sciences.

To halt protein assembly, microRNAs pair up with matching full-length RNA, then fold and twist it, rendering the larger RNA useless. But the RNA pairings are not perfect, and one microRNA can latch on to several hundred RNA strands. "They act like a single circuit breaker to efficiently control hundreds of RNAs," says Civin, the Herman and Walter Samuelson Professor of Cancer Research.

"We're looking for ways to flip these microRNA switches, to control when stem cells grow into new blood cells," says Robert Georgantas, Ph.D., research associate at the Johns Hopkins Kimmel Cancer Center and first and corresponding author of the study.

To identify the key microRNAs, Georgantas sifted through thousands of RNA pieces with a custom-built, computer software program. Its algorithms let the software, fed data from samples of blood and bone marrow from healthy donors, match RNA pairs. The outcome was a core set of 33 microRNAs that match
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