So if we want to figure out what one of the many specialized nerve cells is doing, the easiest way is to simply hijack this system: we force the cell to send ion-based impulses when we tell it to, and watch how the animal’s behavior changes.
The Nobel Committee notes that this idea was so obvious that people tried different methods before the development of optogenetics. But it turns out that “easiest way” didn’t mean “easy,” and most of these methods ultimately didn’t find widespread use because they involved a combination of inserting multiple genes, supplying nerve cells with some very specific chemicals, or using lasers at an intensity that physically damaged the cells.
As it turns out, the ultimate solution lurked in a single-celled alga called Chlamydomonas. The organism’s single cell is remarkably complicated: it has two flagella that help it move and an eyespot that detects the light it moves toward. The organism has been studied for some time as a model for fundamental biological processes.
This is where Hegemann, who was working at Berlin’s Humboldt University at the time, came into play. He and his colleagues managed to connect an electrode to one Chlamydomonas and showed that exposure to a flash of light resulted in a very rapid influx of ions, suggesting that the light triggered the opening of an ion channel. When other scientists began scanning the messenger RNAs he made ChlamydomonasHegemann discovered some genes that resembled a light-activated ion pump found in a species of archaea.
I suspect that these could be responsible for the ion fluxes ChlamydomonasHegemann used RNA interference to block their activity. This restricted the flow of ions in response to light, clearly suggesting that these genes are involved in the organism’s light perception.
