If some of your brain cells suddenly decided to become fat cells, it could cloud your decision-making capacity. Fortunately, early in an organism's development, cells make firm and more-or-less permanent decisions about whether they will live their lives as, say, skin cells, brain cells, or fat cells. These decisions essentially boil down to which proteins, among all the possible candidates encoded in a cell's genes, the cell will tend to make under ordinary circumstances. But exactly how a cell chooses its default protein selections from an overwhelmingly diverse genetic menu is somewhat mysterious. A new study from the Stanford University School of Medicine and collaborating institutions may help solve the mystery. The researchers discovered how a particular variety of the biomolecule RNA that had been thought to be largely irrelevant to cellular processes plays a dynamic regulatory role in protein selection. In unraveling this molecular mechanism, the study also offers enticing clues as to how certain cancers may arise. Dr. Howard Chang, associate professor of dermatology at Stanford, is the senior author of the study, published online on March 20, 2011, in Nature. "All the cells in your body have the same genes, but they don't all make the same proteins," said Dr. Chang, who is also a Howard Hughes Medical Institute Early Career Scientist. In this new study, Dr. Chang and his colleagues identified a novel action by a subset of RNA that reinforces cells' decisions about which combinations of their genes are to be active and which must stay silent. RNA, according to older textbooks, mainly functions as a messenger: a copy of a gene, made by a cell's gene-reading machinery, that can float away from the chromosomes where genes reside to other places in the cell where proteins are made.
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