An engineered cell (green) in a fruit fly follicle (red), or egg case, leaves a trail of fluorescent material as it moves across a fruit fly egg chamber, allowing scientists to trace its path and measure how long it took to complete its journey. Credit: David Bilder, University of California, Berkeley.
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. We think of cells mostly as staying in one spot, quietly doing their work. But in many situations, cells move, often very quickly. For example, when you get a cut, infection-fighting cells rally to the site, ready to gobble up bacterial intruders. 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 move could give scientists new ways to guide those cells or turn off or slow down the movement when needed.
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 inside the fly. To solve this problem, NIGMS-funded researcher David Bilder and colleagues at the University of California, Berkeley, came up with a way to alter fly cells so they could track how the cells behave without removing them from the fly. They engineered the cells to lay down a glowing track of proteins behind them as they moved, leaving a traceable path through the fly’s tissue. The technique, called M-TRAIL (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.
Bilder and his team first used M-TRAIL in flies to confirm the results of past studies of Drosophila ovaries in the lab using other imaging techniques. In addition, they found that M-TRAIL could be used to study a variety of cell types. 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.