Researchers at Albert Einstein College of Medicine have built a microscope powerful enough to view RNA molecules exiting the nucleus of live cells on their way to make proteins. Previous attempts to view inside the nucleus managed to achieve a 200 nm resolution, but the new technique gets down to 20 nm.
Molecules shuttling between the nucleus and cytoplasm are known to pass through protein complexes called nuclear pores. After tagging messenger RNA molecules with a yellow fluorescent protein (which appears green in the accompanying image) and tagging the nuclear pore with a red fluorescent protein, the researchers used high-speed cameras to film messenger RNA molecules as they traveled across the pores. The Nature paper reveals the dynamic and surprising mechanism by which nuclear pores “translocate” messenger RNA molecules from the nucleus into the cytoplasm: this is the first time their pore transport has been seen in living cells in real time.
“Up until now, we’d really had no idea how messenger RNA travels through nuclear pores,” said Dr. Singer. “Researchers intuitively thought that the squeezing of these molecules through a narrow channel such as the nuclear pore would be the slow part of the translocation process. But to our surprise, we observed that messenger RNA molecules pass rapidly through the nuclear pores, and that the slow events were docking on the nuclear side and then waiting for release into the cytoplasm.”
More specifically, Dr. Singer found that single messenger RNA molecules arrive at the nuclear pore and wait for 80 milliseconds (80 thousandths of a second) to enter; they then pass through the pore breathtakingly fast—in just 5 milliseconds; finally, the molecules wait on the other side of the pore for another 80 milliseconds before being released into the cytoplasm.
Messenger RNA molecules (green structures) passing through the nuclear pore (red) from the nucleus to the cytoplasm.The waiting periods observed in this study, and the observation that 10 percent of messenger RNA molecules sit for seconds at nuclear pores without gaining entry, suggest that messenger RNA could be screened for quality at this point.
Press release: Nature Study Shows How Molecules Escape From the Nucleus…
Abstract in Nature: In vivo imaging of labelled endogenous β-actin mRNA during nucleocytoplasmic transport