Synchronized cameras catch messenger RNA on the run

Messenger RNA (mRNA) is the shuttle that carries genetic information across a cell’s nuclear membrane and into the cytoplasm, where the information is translated into a protein sequence. However, the movement of mRNA, which is about 25 nm in diameter, through the nuclear pore complex, roughly 120 nm in diameter, has been difficult to resolve visually since both mRNA and the NPC are well below the 200-nm diffraction limit for optical microscopes. Now, Robert Singer at Yeshiva University’s Albert Einstein College of Medicine in New York and David Grünwald at the Delft University of Technology in the Netherlands have developed a new nanometer-resolution imaging technique that they used to track mRNA’s passage. Emission signals from mRNA and the NPC—labeled with spectrally different fluorescent probes and shown in the image as green and red, respectively—were chromatically separated and tracked by two synchronized high-speed CCD cameras. The researchers achieved 26-nm spatial resolution by resolving the misalignment between the mRNA and the NPC in the images collected before and during tracking by both cameras—a technique they’ve dubbed super-registration microscopy. In their experiments, they also observed that mRNA spent about 5–20 ms crossing the NPC, a fraction of the time it spends at the pore’s entrance and exit—as if, say the researchers, the mRNA was being double screened for quality. That information may support research into understanding how defective mRNA is prevented from escaping the nucleus. (D. Grünwald, R. H. Singer, Nature 467, 604, 2010 http://dx.doi.org/10.1038/nature09438 .)