Twisty chains of proteins keep cells oriented

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Fibers composed of a protein called actin are responsible for human cells’ ability to tell right from left, researchers report in the April Nature Cell Biology. These twisty fibers (below, in yellow; cell’s nucleus in magenta) are part of a cell’s internal scaffolding known as the cytoskeleton. Among other functions, the fibers help cells migrate from one part of a developing embryo to another.

Scientists, including cell biologist Alexander Bershadsky at the National University of Singapore, had amassed evidence that the cytoskeleton enabled cells to distinguish right from left. So Bershadsky’s colleague Yee Han Tee recorded 100 videos of actin fibers organizing themselves inside human foreskin cells placed under the microscope.

The researchers discovered that actin has a natural asymmetry that leads fibers extending from the cell’s edge to twist counterclockwise (see bottom images). This preferred orientation influences navigation and other activities of the entire cell, as if the direction of a screw’s threads could determine how a whole machine works, Bershadsky says. 

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GROWING FIBERS  Actin fibers (green) spread through a human foreskin cell under the microscope. Researchers captured images of the cell every two minutes for about 11 hours.