Cell migration is an integral part of embryonic development in many organisms. Tumor metastasis and wound healing also require cell movement around the body. Unfortunately, it has been very difficult to observe the movement of single cells in tissue culture. Until now, that is. Scientists from Johns Hopkins and the University of North Carolina at Chapel Hill created a light-activation system in fruit flies that allows them to control and watch individual cells moving.
The team, led by Denise Montell of Johns Hopkins, used cells from fruit fly ovaries. These particular cells, called ‘border cells’ must migrate in the fly body to preserve fertility. The border cells were genetically modified in two ways. First, they were altered so that they could no longer respond to normal chemical cues in their environment. Second, they fused a normal fly protein know as Rac to a photoactive plant protein (PA), creating a hybrid protein (PA-Rac) which responds to light by inducing cells containing it to move. Once inserted into the border cells, the researchers were able to use thin beams of light to activate individual cells, or even portions of cells. They were then able to observe the movement of the other cells in the cluster.
According to Montell:
When we activated Rac in even one part of one of these cells — and not in the cell that would be the leader if all was normal — it was as if all the other cells said, Aha! You’ve got more Rac activity so we’re heading your way. It’s amazing to me that somehow the cells sense each others’ levels of Rac activity and collectively decide which way to go.
You can watch a slideshow of cells being induced to move by a green light here, if it doesn’t send you into an epileptic fit.