Humans produce thousands of long, non-coding RNA molecules (lncRNA), most of unknown function, but researchers have identified nearly 500 that regulate cell growth and proliferation.
Such RNAs do not encode proteins. To learn more about them, Daniel Lim and Jonathan Weissman at the University of California, San Francisco and their colleagues systematically inactivated the genes of more than 16,000 lncRNAs across seven different human cell types in culture. They showed that 499 of these lncRNA genes are required for cells to grow and divide. Most of the lncRNAs seemed to have specific functions, affecting growth in just one cell type.