PopSci's Fourth Annual Brilliant 10

John Crocker

University of pennsylvania

He prods cells under his microscope to determine what makes them tick.

John Crocker has spent much of his career probing, as he likes to put it, "gooey, snotty stuff"-known in the trade as soft condensed matter. It may sound disgusting, until you realize that Crocker doesn't study just any snotty stuff. He studies the most important snotty stuff there is: living cells.

Specifically, Crocker is trying to understand the ability of these squishy blobs to sense and respond to their surroundings. "We tend to think of cells as bags of chemicals," he says. "But they have a much more complex sensory apparatus than we give them credit for." In 2000 Crocker devised a measurement technique that is helping him and others investigate the mystery. The advance, says Harvard physicist David Weitz, "has revolutionized the whole field."

Scientists have only recently begun to appreciate how responsive cells are to outside forces. Muscle cells in the uterus trigger labor when stretched by a growing fetus. Gravity-sensitive osteoblasts in the skeleton crank out bone when you gain weight. But how do cells convert physical sensations into chemical signals? Experts suspect that the secret lies within the intricate protein scaffolding that props up the cell's interior, the cytoskeleton.

That's where Crocker's protocol comes in. He puts living cells under a microscope rigged to a high-speed video camera and tracks hundreds of micron-size fat particles as they flit around inside. It's touchy work; a heavy footstep can throw off the readings. But tracking particles within cells is considered the most accurate noninvasive way to see how the cytoskeleton deforms under stress.

Crocker, 37, says his research is yielding "some really big hints" that certain struts in the cytoskeleton serve as a signaling mechanism by popping free in response to external force. His findings could influence fields as disparate as tissue engineering and cancer detection. And Crocker, who began his career slaving over obscure subatomic particles, says it's refreshing to tackle a problem with real-world relevance: "Not necessarily something you can explain on a bumper sticker. But I don't want to be off in a cloud."

-Michael Stroh