Archaerhodopsin variants with enhanced voltage-sensitive fluorescence in mammalian and Caenorhabditis elegans neurons

Probing the neural circuit dynamics underlying behaviour would benefit greatly from improved genetically encoded voltage indicators. The proton pump ​Archaerhodopsin-3 (​Arch), an optogenetic tool commonly used for neuronal inhibition, has been shown to emit voltage-sensitive fluorescence. Here we report two ​Arch variants with enhanced radiance (Archers) that in response to 655 nm light have 3–5 times increased fluorescence and 55–99 times reduced photocurrents compared with ​Arch WT. The most fluorescent variant, Archer1, has 25–40% fluorescence change in response to action potentials while using 9 times lower light intensity compared with other ​Arch-based voltage sensors. Archer1 is capable of wavelength-specific functionality as a voltage sensor under red light and as an inhibitory actuator under green light. As a proof-of-concept for the application of ​Arch-based sensors in vivo, we show fluorescence voltage sensing in behaving Caenorhabditis elegans. Archer1’s characteristics contribute to the goal of all-optical detection and modulation of activity in neuronal networks in vivo