Cells are the basis of the living world. Our cells make up the tissues and organs of our bodies. Bacteria are also cells, living sometimes alone and sometimes in groups called biofilms. They think of cells mostly as staying in one spot, quietly doing their work. But in many situations, cells move, often very quickly. Then, platelet cells along with proteins from blood gather and form a clot to stop any bleeding. And finally, skin cells surrounding the wound lay down scaffolding before gliding across the cut to close the wound.

This remarkable organization and timing is evident right from the start. Cells migrate within the embryo as it develops, so that body tissues and organs end up in the right places. Harmful cells use movement as well, as when cells move and spread (metastasize) from an original cancer tumor to other parts of the body. Learning how and why cells could give scientists new ways to guide those cells or turn off or slow down the movement when needed.

Glowing Breadcrumbs

Scientists studying how humans and animals form, from a single cell at conception to a complex body at birth, are particularly interested in how and when cells move. They use research organisms like the fruit fly, Drosophila, to watch movements by small populations of cells. Still, watching cells migrate inside a living fly is challenging because the tissue is too dense to see individual cell movement. But moving those cells to a dish in the lab might cause them to behave differently than they do on the fly.

 The technique, called M-TRAIL (a matrix-labeling technique for real-time and inferred location), allows the researchers to see where a cell travels and how long it takes to get there. The new technique also could allow a cell's movement to be tracked over a longer period than other imaging techniques, which become toxic to cells in just a few hours. This is important because cells often migrate for days to reach their final destinations.

Once it's turned on, this protein network starts up the cell's movement machinery, including its cellular skeleton, called the cytoskeleton. In response to signals from the network, the cell begins to change shape, an early step in cell migration. The movement network can start up at random, but it also responds to cues from outside the cell. Devreotes and his team tested this by putting the amoeba cells in a dish of swirling water.

The researchers found that the network proteins within the cells responded to the swirling water in the same way that they respond to other environmental cues.  Once on the move, different cells use different techniques to propel themselves forward. Some, like an amoeba or our white blood cells, reach out with bumps called pseudopods, cellular "feet" that pull the cell forward.

Others create a large fan-shaped bulge all along the leading edge of the cell that drives it along, and still, others make waves from their centers that ripple through the cell, pulling them forward. Scientists had thought that each kind of cell used only one of these modes to move. Instead, when Devreotes and his team changed the proteins in the movement network inside cells, they found that amoebas altered their movement behavior, switching from pseudopods to fans to rippling waves and back again

Moving as a group has benefits for bacteria, but it is also expensive. So, bacteria want to make sure that none of their competitors can use the surfactant they make for a free ride. Bacteria have evolved many methods for telling their close relatives from their enemies.

They even release antibiotics that they are immune to, but that will kill bacterial cells not related to them. Kolter and his team believe that the weapons bacteria use to compete successfully also make them into close-knit colonies and promote cooperation. Learning about the balance between cooperation and competition in bacterial colonies, Chimileski said, will help clarify what happens in places like our gut microbiomes, which, we are learning, are highly complex microbial environments very important to our health.