Because they can snake several feet from the spinal cord to the extremities, peripheral nerves are often quite long -- sometimes 100,000 times longer than other cells in the body. The transportation of materials along this entire length is an extremely long and complicated process that can take days or even weeks. Studying this process has always been a complicated proposition, but Bianxiao Cui and her Stanford colleagues have demonstrated a new way of observing this transport by tagging single molecules, called nerve growth factors, with "quantum dots" that can be followed with a powerful microscope as they move along live neurons.
The researchers' technique is analogous to looking at a dark highway from the window of an airplane. The dark, invisible lanes of roads are microtubules, the skeleton of the cell. The nerve growth factor molecules ride in the cars that are illuminated by their quantum dot headlights. One thing Cui and her colleagues have observed, which has never been seen before, is that packages in transport can jump from one microtubule to another as they move along -- like cars switching lanes as they roll down the highway. They also discovered that the majority of those cars are single passenger; they only contain a single nerve growth factor molecule.
Scientists have known for a long time that these proteins are essential, since they help the nerve cells survive by regulating gene expression. But Cui and her colleagues showed that even a single molecule of nerve growth factor is enough to trigger the transport process and sustain signaling during axonal transport to the cell body. (Paper LSThB3, "Single Molecule Imaging of Axonal Transport in Live Neurons" is at 9 a.m. Thursday, Oct. 15).
WATCHING PROTEINS FOLD
One of the most important biological action
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