For decades, researchers have used petri dishes（培养皿） to study cell movement. These classic tissue culture tools, however, only permit two-dimensional movement, very different from the three-dimensional movements that cells make in a human body. In a new study from the University of Pennsylvania and National Institute of Dental and Craniofacial Research, scientists used an innovative technique to study how cells move in a three-dimensional matrix, similar to the structure of certain tissues, such as the skin. They discovered an entirely new type of cell movement whereby the nucleus helps propel cells through the matrix like a piston（活塞） in an engine, generating pressure that thrusts the cell's plasma membrane forward.

"Our work elucidated a highly intriguing question: how cells move when they are in the complex and physiologically relevant environment of a 3-D extracellular matrix," said Hyun (Michel) Koo, a professor in the Department of Orthodontics at Penn's School of Dental Medicine. "We discovered that the nucleus can act as a piston that physically compartmentalizes the cell cytoplasm（细胞质） and increases the hydrostatic（流体静力学的） pressure driving the cell motility within a 3-D matrix."

Koo worked with lead author Ryan Petrie and senior author Kenneth Yamada, both of the National Institutes of Health's NIDCR, on the study, which is published this week in Science.

"We think it's a very important normal physiological mechanism of cell movement that has not been characterized previously," Petrie said.