Organisms need to sense their environment. By sensing, they can develop, heal wounds, protect against invaders, and create blood vessels. Chemotaxis, or directional sensing, allows cells to detect chemicals with exquisite sensitivity. Some chemotactic cells can sense chemical gradients that differ by only a few percent from a cell's front to its back. Although discovery of the molecule types involved in chemotaxis, as with other kinds of cell signaling events, has mounted, the details of how this dynamic process works is somewhat shrouded in mystery. But in the last few years, researchers have applied sophisticated imaging technologies to dissect this process, and now the details are coming to light.

The phenomenology itself is decades old. Neutrophil migration was observed in the early part of the 20th century, and was captured on film 50 years ago by the late David Rogers of Vanderbilt University. (Rogers' film can be viewed on the...

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