Long noncoding RNAs (lncRNAs) are mysterious molecules. They are almost-proteins—transcripts of about 200 or more nucleotides that appear not to encode proteins. Given their noncoding status, it is perhaps surprising that many lncRNAs are expressed in very specific anatomical or developmental patterns, suggesting that their regulation is of biological importance. At the cellular level, most lncRNAs, also called large intergenic noncoding RNAs (lincRNAs), are localized to the nucleus. In addition, most lncRNAs either overlap with genes that encode proteins, are transcribed antisense to genes that encode proteins or are expressed as intergenic or intronic regions.
But why spend energy tightly regulating the expression and localization of RNA molecules that don’t eventually end up as proteins? And what do they actually do? Recent advances in RNA sequencing are providing a look at these mysterious molecules, which can be perused in new databases such as the Human Body Map lincRNAs catalog developed by the Broad Institute, Harvard University and the Massachusetts Institute of Technology. Realizing the many lncRNAs out there whose functions we have yet to learn, it appears today’s knowledge is just the tip of the lncRNA iceberg.