Scientists from the Broad Institute and MIT have created a groundbreaking technique to monitor gene activity in living cells over time, without harming them. This method, published in the journal Cell, allows researchers to observe how genes are expressed as cells develop or react to external influences. Instead of destroying cells to study their RNA — the molecular blueprint for protein production — the new approach uses virus-like particles that cells naturally produce to transport RNA out of the cell. The technique involves modifying mammalian cells to produce a protein found in retroviruses. This protein helps package both the cell’s RNA and viral RNA into tiny, virus-like particles. These particles then detach from the cell and enter the surrounding liquid medium. Scientists can collect and analyze this RNA from the medium without damaging the cells, allowing them to repeatedly sample gene activity over time. This method has been tested on a variety of cell types, including cancer cells, stem cells, neurons, and primary human cells. Researchers have also applied it to three-dimensional cell structures and "organ-on-a-chip" systems, which simulate the functions of real organs. These applications make the method particularly useful for studying complex cellular processes and disease mechanisms in a more realistic biological context. The new technique offers a powerful tool for scientists to track changes in gene expression in living cells, which could advance research in areas such as development, disease progression, and drug testing. By enabling non-invasive, repeated sampling, the method could provide deeper insights into how cells and tissues evolve over time, both under normal conditions and in response to various stimuli.