Double-stranded RNA molecule.

The age of an RNA molecule (artist’s impression of double-stranded RNA) can be estimated with a protocol that involves an RNA-editing protein. Credit: Laguna Design/SPL

Biotechnology

The timestamp that can tell an RNA molecule’s age — to the hour

Technique allows scientists to complete a timeline for gene activity in a single cell.

An RNA-editing tool that ‘timestamps’ RNA molecules reveals not only which genes in a cell are turned on at any one time, but also when they were turned on.

When a gene is switched on, it triggers the production of RNA molecules that carry the information needed to make a specific protein. Scientists hoping to understand a cellular process often sequence the RNA molecules present at a given moment in a single cell. But researchers have lacked a reliable way to determine when a particular gene became active.

A team led by Edward Boyden at the Massachusetts Institute of Technology in Cambridge and Fei Chen at the Broad Institute of Harvard and MIT, also in Cambridge, tagged genes with a genetic sequence that is recognized by an RNA-editing protein. After these genes had synthesized RNA, the protein made chemical changes to the molecule, adding progressively more edits over time.

When the researchers then sequenced the RNA molecules, they could assume that those with more chemical edits were older than those with fewer edits. The system can narrow down an RNA molecule’s age to within roughly one hour.