To deal with the first problem, Benjamin Lin, a member of Levchenko's team who led the study, joined forces with Inoue's research group to take advantage of a novel method relying on a small molecule able to get between the fat molecules of the cell membrane and into the cell. Once inside, it would bind to two slightly modified proteins in the network that stimulates movement; the new complex of three molecules would in turn trigger the critical protein Rac, which falls somewhere in the middle of the choreographed chain reaction that leads to movement. By analyzing which enzymes in the chain reaction were ultimately activated by the synthetic molecule and which weren't, the researchers could tell whether they were downstream or upstream of Rac in the chain.
To create a fine enough biochemical gradient of the synthetic molecule to guide a cell in a specific direction, the researchers built a silicone-based chip with tiny liquid-dispensing channels running along the surface. When they loaded the channels with a solution containing the synthetic molecule, and placed human cells on the surface, they could stimulate one side of a cell more than the other, and induce it to move. "Neither synthetic molecules nor microfluidic devices had been used before in this particular way, and the results exceeded all our expectations," says Levchenko. "The cells responded very dramatically, moving in the direction we specified, and changing their shapes."
In addition to providing researchers with powerful new tools for studying cell movement, the experiment is a step forward for the budding field
|Contact: Vanessa McMains|
Johns Hopkins Medicine