Rats and mice aren’t the only ones who can solve lab mazes. A new study suggests single-celled organisms—and even individual cancer cells—are just as adept, using chemical signals to find their way through complex mazes hundreds of times their size.
Individual cells, whether cancer cells, skin cells, or single-celled organisms like bacteria, generally know where to go by sensing attractive chemicals in their environments and moving toward them, a process called chemotaxis. This basic type of navigation works best for short distances, generally less than half a millimeter. But when cells traverse longer, more complex paths, they can’t just passively follow a chemical gradient: They need to process the chemicals around them in real time to pick the best way forward.
To figure out how cells do this, researchers tested two known for going the distance—a soil-dwelling amoeba (Dictyostelium discoideum) and mouse pancreatic cancer cells. The researchers designed microscopic mazes with a pool of attractant chemicals at the end; they also filled the maze with the same chemicals so cells could build their own chemical trails. The miniature labyrinths had plenty of twists and turns—a perfect proxy for the complex path through soil or to a blood vessel.
Both cell types successfully maneuvered through the mazes, the researchers report today in Science, making it through various 0.85-millimeter-long mazes. The faster moving amoebas then tackled a longer one designed to mimic the famous Hampton Court Palace hedge maze outside of London (see video). Because the cancer cells moved so slowly, they likely would have perished during the longer journey.
By breaking down the chemicals as they moved through the maze, the first wave of amoeba cells was able to distinguish between the maze’s dead ends—which had limited amounts of the attractive chemical—and the correct path forward. But subsequent waves of cells weren’t so lucky. In nature, leading cells give off signals to their trailing counterparts to follow them. In the experiment, scientists modified cells to make such communication impossible. After the pioneers broke down the chemicals—essentially clearing them from the path—the stragglers were left unsure of where to go next.