Using neat genetic tricks with fruit flies, scientists from Johns Hopkins School of Medicine have found the key signal that allows a group of normally stationary cells in the ovary to travel, they report in the current issue of Cell.
Because fruit fly genetics are similar to but vastly simpler than human genetics, understanding the signals that mobilize the ovary cells may help clarify how human cancer cells invade distant tissues, says Denise Montell, Ph.D., associate professor of biological chemistry in the school's Institute for Basic Biomedical Sciences.
"Cells usually hold on to their neighbors, so a lot of things have to change for a cell to become migratory," says Montell, who has been studying this process in flies for 12 years. "We've now found the first signal that seems to be sufficient to get cells moving."
With funding from the American Cancer Society and the National Institutes of Health, graduate student Debra Silver examined thousands of mutant fruit flies and identified a protein called "Unpaired" that activates stationary cells.
The fruit fly ovary consists of about one hundred egg chambers, each made of 16 cells -- 15 "nurse" cells and one oocyte, which becomes the egg -- surrounded by a layer of several hundred epithelial cells. At a certain point in development of the egg, a single small cluster of these epithelial cells detaches from the others and moves from the edge of the egg chamber to the center, sliding between nurse cells and coming to rest at the edge of the oocyte.
The cluster consists of two interior "polar" cells and a covering of four to eight "border" cells. Other researchers have shown that, while key to the migratory process, the polar cells can't move without the help of border cells. But until now it wasn't known how polar cells recruit border cells to be their vehicle.