Tools for observing and controlling specific molecular or physiological pathways in intact cells and tissues are opening up new frontiers in the understanding and engineering of complex biological systems and even pointing the way toward novel kinds of therapy and prosthetic for treating human disease. One of the most popular strategies is to utilize what has come to be known as an “optogenetic” strategy— namely, to create a genetically encoded optical reporter of biological activity, or a light-driven actuator of biological signaling, and then to express the gene that encodes for this molecule in a specific cell or set of cells, often within an intact tissue or organism. Then, the investigator uses light to perform the readout of the biological system state by monitoring cells expressing optical reporters, say using a microscope, or to alter the biological system via illuminating it so that cells expressing the light-driven actuator are selectively altered.
