A new movie promises to expand the survival genre, the cell survival genre, that is. Never before have cells reacting to life-threatening stress been depicted so dynamically. Using novel antibody tagging technology and a custom fluorescence microscope, scientists based at Colorado State University imaged the stress response in real time. Not only did the scientists bring movement to a genre still dominated by fixed cell imaging, but they also ensured a colorful, high-resolution presentation. In fact, the scientists were able to zoom in on single molecules.
Rather than show every aspect of the stress response, the scientists focused on just one: the formation of stress granules, or ribonucleoprotein (RNP) granules. These are membrane-less blobs of proteins and RNA molecules that form when the cell feels the need to hunker down. It might do so in response to oxygen deprivation, overheating, or an invading toxin.
Telling the RNP story requires an ensemble cast, particularly since the dynamics of the mRNA components within and near the RNP granule surface remain poorly characterized. Yet the Colorado State University team, led by biochemists Roy Parker, PhD, and Timothy J. Stasevich, PhD, found a way to include several key molecules and their action sequences, as described in an article (“Multicolour single-molecule tracking of mRNA interactions with RNP granules“) that appeared recently in Nature Cell Biology.
“We used multicolor single-molecule tracking to quantify the precise timing and kinetics of single mRNAs as they exit translation and enter RNP granules during stress,” the article’s authors wrote. “We observed single mRNAs interacting with stress granules and P-bodies, with mRNAs moving bidirectionally between them.”
With single-molecule precision, the researchers have captured individual mRNA molecules interacting with stress granules, revealing how, when, and where the mRNAs move around—a process never before witnessed from start to finish. They have shown definitively, among other things, that RNA translation is completely silenced before the mRNAs enter the stress granules.
“I think seeing is believing, and that’s our contribution here,” said Stasevich. “We are using live cells as test tubes to study dynamic processes that have never been seen before. The ability to image these processes at the single-molecule level in living cells will be a powerful tool to better understand the cellular stress response in normal and diseased cells.”
By going to the movies with Stasevich’s team, the cellular stress response has come alive in colorful detail, shedding light on previously hidden details. Among the paper’s major findings is that while some RNAs come and go at the surfaces of the granules, some are peculiarly stuck, as if tethered in molasses, the researchers said.
“Live and fixed cell imaging demonstrated that mRNAs can extend beyond the protein surface of a stress granule, which may facilitate interactions between RNP granules,” the article’s authors indicated. “Thus, the recruitment of mRNPs to RNP granules involves dynamic, stable, and extended interactions affected by translation status, mRNA length, and granule size that collectively regulate RNP granule dynamics.”