Plants use light to tell them where to move and how to grow. What if animal cells could be directed in the same way? Now they can. Researchers at the University of California San Francisco have modified mouse cells with plant proteins so that they will change shape and move in response to signals of light. As described in the recent publication in Nature, Scientists were able to get the mammalian cells to follow a weak red light and pull away from infrared light. Similar techniques can be used to control other cell functions besides shape and movement. One day, researchers hope, such modifications could be performed on human cells to help direct the repair of spinal injuries and allow cells to reconnect across gaps.
While similar work has been performed in yeast and bacteria, this experiment marks the first time that mammal cells have been upgraded in this fashion. I’m impressed by the way that researchers got cells to move like miniature remote control robots, but there are greater implications. By inserting key plant proteins (called phytochromes) into mammal cells, researchers have created a light-based switch that they can insert into many different chemical pathways. The UCSF team focused on the pathways which affect the cytoskeleton, but they could have targeted protein interactions that control how food is processed, or functions that impact cell life span. Imagine using specially tuned light signals to keep some cells (say those with cancer) from processing nutrients, or encourage other cells (say those in an area with nerve damage) to repair and reproduce themselves. With the protein-based light switch, scientists could change a cell’s chemical functions temporarily, and repeat the process as needed later. That’s an amazingly powerful tool.
When manipulating the mouse cells, researchers used combinations of red light and infrared light. These types of light directly affect the plant phytochromes that were inserted into the mammal cells. Basically, one type of light will induce one kind of chemical reaction, while the other light will stop or reverse that reaction. By bathing the mouse cell in IR and providing a single spot of red light, the researchers were able to get the cell to deform and follow the red spot as it moved over time.
While it took many minutes for the cell to move as the researchers desired, the chemical reactions that the light was causing happened much quicker. The UCSF team was able to control the position of these reactions down to the micron level, and with a response time around one second. This precision could have important implications if surgeons one day used this sort of technique to repair damage in the body. It could also facilitate fine control of the functions of the cell if and when researchers try to control chemical pathways unrelated to cell movement.
I’ve always been impressed with how many technological advancements in biology can be traced to a scientist taking the parts of one living thing and sticking them inside of another. Putting plant proteins in mammal (or some day, human) cells gives us the means to interact with those cells via light. But why stop there? We could have skin cells that produce chameleon pigments or blood cells with the antifreeze from Artic bacteria. Most of this research would seem to be leading towards very controlled forms of transhumanism. Humans have always shaped their bodies to match their needs, but with tools like these we may gain access to changes that are both profound and reversible.
[image credit: Wendell Lim et al, Nature]
