Fly cells reveal clues to cancer metastases

Scientists from Johns Hopkins School of Medicine, US, have found the key signal that allows a group of normally stationary cells in the ovary to travel.

Because fruit fly genetics are similar to but vastly simpler than human genetics, understanding the signals that mobilise the ovary cells may help clarify how human cancer cells invade distant tissues, says Denise Montell, associate professor of biological chemistry in the school's Institute for Basic Biomedical Sciences.

"Cells usually hold on to their neighbours, 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 have now found the first signal that seems to be sufficient to get cells moving."

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 centre, 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 cannot move without the help of border cells. But until now it was not known how polar cells recruit border cells to be their vehicle.

"Genes involved in cell migration are very important," says Montell. "They are probably involved in early embryo development."

The next step is to examine ovarian cancer tissue to see if the so-called JAK/STAT pathway (which was already known to help regulate cell division and cell survival in humans) regulates the mobility of human cancer cells. In general, tumours are not particularly dangerous until they begin moving, a process called metastasis. While much is understood about how cancer cells travel, it is not well understood how they let go of the original tumour or lodge elsewhere.