In the body, cells move like flocks of birds or schools of fish

Biologists look to collective behavior of animals to help explain cell movement

bird flock

TRAVEL TIPS  Bird follow rules when flocking. Cells in the body migrate in groups following similar rules, cell biologists are discovering.

Adam/flickr (CC BY 2.0)

SAN DIEGO — Cell biologists are taking clues from marching ants, flocking birds and other animals to learn how groups of cells move through the body.

Such studies are yielding insights about cell movement during development as well as the spread of cancer. Learning about cells’ social interactions may give researchers new ways to peer pressure cells into good behavior.

Cell biologists have traditionally studied individual cells or how groups of physically connected cells move. It’s only in the past few years that researchers have begun to regard cells as individuals with collective behavior. Taking cues from the linked movements of animals helps researchers “understand how cells, which everybody assumed had minds of their own, could possibly move as a group,” says Brian Stramer, a cell biologist at King’s College London.

Developmental biologist Roberto Mayor and colleagues have collected evidence that the migration of some important developmental cells is akin to the movement of swarming locusts. Mayor, of University College London, described the mass migration of neural crest cells December 13 at the annual meeting of the American Society for Cell Biology.

Neural crest cells are developmentally flexible cells in embryos that help form the bones and cartilage of the face, some nerves and brain cells, smooth muscle and other tissues. Some scientists have proposed that changes in early movements of these cells may lead to juvenile physical features in domesticated animals (SN: 8/23/14, p. 7).

Like locusts that cringe away from nipping neighbors, neural crest cells repel each other thanks to a process known as “contact inhibition of locomotion,” Mayor and colleagues found. Avoidance can increase the ability of cells to move in groups; cells that move astray and bump into a neighbor change course and move in the right direction again. A large crowd governed only by avoidance tactics, though, tends to break into smaller cliques, the researchers discovered in computer simulations. Cells are not just repelled by each other; they are also often attracted to other cells. That attraction causes cells to play follow-the-leader. On its own, attraction produces a group of cells that don’t get very far, computer simulations showed. A balance between avoidance and attraction produces the most efficient mass migrations, the simulations suggest.

Neural crest cells and other embryonic cells called placode cells display just the sort of run-and-chase behavior that enables effective migration, Mayor said. Placode cells give rise to sense organs or groups of nerves called ganglions. When neural crest cells make contact with placode cells, contact inhibition causes the placode cells to run away. The neural crest cells are attracted to the placodes and give chase, said Mayor, whose group is learning some of the molecular details of this attraction and repulsion.

Cancer cells may also follow group behavior rules seen in swimming, swarming and flocking animals. Brain tumors organize themselves into streams and swirls reminiscent of patterns made by schools of fish, researchers reported December 14 at the cell biology meeting. Neurobiologist Pedro Lowenstein at the University of Michigan in Ann Arbor teamed up with mathematician Sebastien Motsch of the Arizona State University in Tempe to study movement of glioma cells.

Gliomas are tumors that run fingerlike projections through the brain. Each finger is a stream of cells about 10 to 20 cells wide. Motsch and colleagues constructed computer simulations of the cells’ movement, considering each as an independent entity and taking into account connections and repulsion among tumor cells. A picture emerged showing brain tumors as self-organizing structures that form streams, swirls and spheres. The simulations also showed that cells leading the pack would become elongated.

Lowenstein and colleagues tested the computer predictions in the lab and found that round cells don’t move, but stretched-out ones do. Adding mobile cells into a group of stationary ones got the sedentary cells to move. That’s bad news for patients, the researchers discovered. Mice in which brain tumors don’t form streams live about 200 days, while those whose brain tumor cells stream died after about 50 days. If this holds up in people, discerning mobile cancer cells from stationary ones might help determine the aggressiveness of a tumor.

Editor’s Note: This story was updated December 23, 2015, to correct which kind of muscle neural crest cells help to form.

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