Optimization of genetically encoded GABA indicator

The GENIE Project Team at HHMI Janelia has developed a  second-generation genetically encoded GABA indicator, in collaboration  with Jonathan Marvin and Loren Looger. The sensor is based on iGABASnFR  (1), and has the following features, tested extensively in cultured  neurons:

Positive-going version (iGABASnFR2) and negative-going version (iGABASnFR2n)
iGABASnFR2: 4x higher sensitivity to APs than iGABASnFR, iGABASnFR2n: 2x higher sensitivity to APs than iGABASnFR.
Both enable single-AP high-speed imaging
Enables detection of signal in individual dendrites and synaptic boutons
Higher affinity for GABA (iGABASnFR2: EC50: 6.4±0.2 μM, ~7x tighter than iGABASnFR, ΔF/Fmax=0.5±0.05, ~2x higher than iGABASnFR)
Imaged with standard GFP filter set