An optogenetic application of proton pump ArchT to C. elegans cells.

Application of novel light-driven ion channel/pumps would benefit optogenetic studies of Caenorhabditis elegans. A recent study showed that ArchT, a novel light-driven outward proton pump, is >3 times more light-sensitive than the Arch proton pump. Here we report the silencing effect of ArchT in C. elegans cells. ArchT expressed by using a body-wall muscle or pan-neuronal-promoters caused a quick and reliable locomotion paralysis when worms were illuminated by green light. Unlike the report on mouse neurons, however, light sensitivity of ArchT is similar to that of Arch in C. elegans. ArchT-mediated acute silencing of serotonergic neurons quickly triggered backward locomotion. This response was abolished in the presence of exogenously added serotonin, suggesting that, in a normal situation, serotonin is secreted in a constitutive fashion to repress backward movement.