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Channelrhodopsin-2-XXL, a powerful optogenetic tool for low-light applications.

ABSTRACT: Channelrhodopsin-2 (ChR2) has provided a breakthrough for the optogenetic control of neuronal activity. In adult Drosophila melanogaster, however, its applications are severely constrained. This limitation in a powerful model system has curtailed unfolding the full potential of ChR2 for behavioral neuroscience. Here, we describe the D156C mutant, termed ChR2-XXL (extra high expression and long open state), which displays increased expression, improved subcellular localization, elevated retinal affinity, an extended open-state lifetime, and photocurrent amplitudes greatly exceeding those of all heretofore published ChR variants. As a result, neuronal activity could be efficiently evoked with ambient light and even without retinal supplementation. We validated the benefits of the variant in intact flies by eliciting simple and complex behaviors. We demonstrate efficient and prolonged photostimulation of monosynaptic transmission at the neuromuscular junction and reliable activation of a gustatory reflex pathway. Innate male courtship was triggered in male and female flies, and olfactory memories were written through light-induced associative training.

SUBMITTER: Dawydow A

PROVIDER: S-EPMC4183338 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Channelrhodopsin-2-XXL, a powerful optogenetic tool for low-light applications.

Dawydow Alexej A Gueta Ronnie R Ljaschenko Dmitrij D Ullrich Sybille S Hermann Moritz M Ehmann Nadine N Gao Shiqiang S Fiala André A Langenhan Tobias T Nagel Georg G Kittel Robert J RJ

Proceedings of the National Academy of Sciences of the United States of America 20140908 38

Channelrhodopsin-2 (ChR2) has provided a breakthrough for the optogenetic control of neuronal activity. In adult Drosophila melanogaster, however, its applications are severely constrained. This limitation in a powerful model system has curtailed unfolding the full potential of ChR2 for behavioral neuroscience. Here, we describe the D156C mutant, termed ChR2-XXL (extra high expression and long open state), which displays increased expression, improved subcellular localization, elevated retinal a ...[more]

PMID: 25201989

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Project description:Optogenetic defibrillation of hearts expressing light-sensitive cation channels (e.g., ChR2) has been proposed as an alternative to conventional electrotherapy. Past modeling work has shown that ChR2 stimulation can depolarize enough myocardium to interrupt arrhythmia, but its efficacy is limited by light attenuation and high energy needs. These shortcomings may be mitigated by using new optogenetic proteins like Guillardia theta Anion Channelrhodopsin (GtACR1), which produces a repolarizing outward current upon illumination. Accordingly, we designed a study to assess the feasibility of GtACR1-based optogenetic arrhythmia termination in human hearts. We conducted electrophysiological simulations in MRI-based atrial or ventricular models (n = 3 each), with pathological remodeling from atrial fibrillation or ischemic cardiomyopathy, respectively. We simulated light sensitization via viral gene delivery of three different opsins (ChR2, red-shifted ChR2, GtACR1) and uniform endocardial illumination at the appropriate wavelengths (blue, red, or green light, respectively). To analyze consistency of arrhythmia termination, we varied pulse timing (three evenly spaced intervals spanning the reentrant cycle) and intensity (atrial: 0.001-1 mW/mm2; ventricular: 0.001-10 mW/mm2). In atrial models, GtACR1 stimulation with 0.005 mW/mm2 green light consistently terminated reentry; this was 10-100x weaker than the threshold levels for ChR2-mediated defibrillation. In ventricular models, defibrillation was observed in 2/3 models for GtACR1 stimulation at 0.005 mW/mm2 (100-200x weaker than ChR2 cases). In the third ventricular model, defibrillation failed in nearly all cases, suggesting that attenuation issues and patient-specific organ/scar geometry may thwart termination in some cases. Across all models, the mechanism of GtACR1-mediated defibrillation was voltage forcing of illuminated tissue toward the modeled channel reversal potential of -40 mV, which made propagation through affected regions impossible. Thus, our findings suggest GtACR1-based optogenetic defibrillation of the human heart may be feasible with ≈2-3 orders of magnitude less energy than ChR2.

Dataset Information

Channelrhodopsin-2-XXL, a powerful optogenetic tool for low-light applications.

Publications

Channelrhodopsin-2-XXL, a powerful optogenetic tool for low-light applications.

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