Fig. 3. Generality of the approach to engineer positive-going eFRET GEVIs.

Each panel shows a schematic of the voltage indicator construct (left), a fluorescence image of a neuron in culture expressing this voltage indicator (center), and simultaneous recording of fluorescence (right top) and membrane potential (right bottom) in response to current injection. Fluorescence image scale bar = 20 μm. Simultaneous voltage and fluorescence traces are representative of N ≥ 3 cells. a Positron labeled with two different colors of fluorescent dye, JF₅₂₅ (top) and JF₅₈₅ (bottom). b Ace2 rhodopsin bearing the signal-inverting mutations described and fused to the different color FP domains mNeonGreen (top) and mRuby3 (bottom). c Different rhodopsin domains (Mac, top and Ace1, bottom) bearing mutations analogous to the described signal-inverting mutations described, fused to HaloTag, and labeled with JF₅₂₅.