Tracking mRNA Particles

The motion of individual messenger RNA particles can be tracked in three dimensions with nanometer-scale precision via optical imaging, W. E. Moerner and coworkers at Stanford University report (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1012868107). Using a recently developed 3-D microscopy method with a so-called double-helix point spread function, the researchers followed the position of single mRNA particles in live yeast cells. Because yeast cells are spherical, 3-D measurements are necessary to provide complete information about the dynamics of the system. In fact, they found that without information about the third dimension, particle motion could be incorrectly classified. The Stanford team tracked the motions of an mRNA that is expressed at low levels and doesn’t localize to particular cellular regions. The researchers used two probability tests to categorize the motion of the mRNAs as being diffusive, confined, or directed. The motion of the particles was predominantly random (diffusive), they note, although examples of confinement and directed motion were observed that could not be explained by Brownian motion. Moerner and coworkers hope that their study will provide a quantitative benchmark for the future analysis of localized mRNA particles.