Stem cells sense stiffness.

Stem cells can sense the texture of whatever medium they're growing on and use this quality to guide their fate, according to new research.

Unlike other cells in the body, stem cells start out with the ability to morph into many types of tissues. Scientists have proposed transplanting these cells to repair parts of the body damaged by illness or wear. However, before that scenario can play out in the clinic, researchers must learn how to tightly control what tissues stem cells become.

Dennis E. Discher of the University of Pennsylvania in Philadelphia and his colleagues had a hunch that a stem cell's fate might depend on the texture of the growth medium that researchers use to raise the cells in the lab. To test their theory, the researchers worked with a type of stem cell isolated from adult bone marrow. These mesenchymal cells have the capacity to become nerve cells, muscle, or bone.

The scientists found that growing the cells in a dish of soft gel, analogous to brain tissue, yielded nerve cells. Stem cells grown on a harder gel became muscle, and those grown on the stiffest gel became bone.

Discher's team reports in the Aug. 25 Cell that molecular motors inside the cells cause them to grip the medium they're on and determine its texture.--C.B.