Lights, Cameras, Action: Probing the Nervous System with Light
Ehud Isacoff, University of California, Berkeley, USA
A major challenge for biology is to develop new ways of determining how proteins operate in complexes in cells. An attractive approach is to use light as both input and output to probe molecular machines in cells. Our approach has been to synthesize chemical compounds that we call “Photoswitched Tethered Ligands” or “PTLs”, which we attach to a protein of interest. The site of attachment is designed into the protein to be at a precise distance from a binding site for a special molecule that naturally blocks the activity of the protein or turns that activity on. The design is such that the molecule can be switched on and off with two different colors of light. The speed of optical switching is very fast, taking place in ~1 millisecond, i.e. at the rate of the fastest nerve impulse.
We have employed this approach to endow proteins from the nervous system with sensitivity to light. The proteins include ion channels, transmitter receptors and enzymes. The light-activated and light-blocked proteins work in a variety of organisms, including isolated brain neurons, neurons in intact brain slices, neurons in the retina in live rodents, and in behaving zebrafish sensory and motor systems.
I will describe:
1) the chemical and protein engineering that we use to make light-switched proteins,
2) the way that the proteins are introduced genetically into specific cells in the nervous system,
3) the kinds of questions that can be asked about how signals are transmitted between nerve cells, how the transmission process is adjusted by experience to mediate learning and memory,
4) how these so-called “opto-genetic” approaches can be used to understand the neural circuits underlying behavior.