Red-Shifted Calcium Indicators for Artifact-Free Optogenetic Imaging
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Solution Overview
Problem
Existing genetically encoded calcium indicators (GECIs) suffer from limitations such as decreased sensitivity, complicated photophysics, lysosomal accumulation, and blue-light activated photoswitching behavior, which hinder their use in conjunction with blue-light activated optogenetic actuators for all-optical stimulation and observation, especially in the near-infrared (NIR) optical window due to dim fluorescence.
Innovation Solution
The use of red-shifted GECIs, such as K-GECO1, NIR-GECO1, and NIR-GECO2, in conjunction with optogenetic actuators activated by different wavelengths, allows for artifact-free all-optical stimulation and observation of calcium dynamics in cells, enabling precise control and monitoring of cellular physiology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If red GECIs (such as RCaMP variants) are used for imaging calcium transients, then the excitation wavelength is shifted to red to avoid interference with blue-light activated optogenetic actuators, but the sensitivity is decreased
Solution Approach 1:
The patent applies parameter changes by modifying the spectral properties of GECIs through genetic engineering to achieve red-shifted excitation wavelengths (570-650 nm) that do not overlap with blue-light optogenetic actuators (450-480 nm). This spectral parameter change resolves the contradiction by enabling compatible wavelength separation while maintaining imaging functionality, though sensitivity trade-offs are acknowledged and managed through optimized indicator design.
2Illumination intensity
If R-GECO variants are used for calcium imaging, then red-shifted fluorescence is achieved, but complicated photophysics and lysosomal accumulation occur
Solution Approach 1:
The patent applies the extraction principle by removing the problematic photoswitching domain (Photoactivatable Red Fluorescent Protein or PAF) from the GECI construct. By taking out this problematic component that causes complicated photophysics and lysosomal accumulation, the patent achieves simpler, more reliable imaging while maintaining red-shifted fluorescence properties through alternative molecular designs.
Solution Approach 2:
The patent converts the harmful photoswitching behavior into a beneficial artifact-free imaging system. By eliminating the photoswitching domain that caused reliability issues, the patent transforms a problematic feature into a solution that enables clean, interpretable calcium imaging signals without the confounding effects of light-induced photoswitching or organelle mislocalization.
3Object-affected harmful factors
If NIR GECIs are used for in vivo imaging, then tissue scattering and absorption are minimized, but the fluorescence intensity is dim
Solution Approach 1:
The patent applies parameter changes by optimizing the spectral properties of GECIs to achieve excitation and emission wavelengths in the red-to-NIR range (570-650 nm excitation, 590-700 nm emission). This parameter optimization balances tissue penetration depth with sufficient fluorescence intensity, positioning the indicators in the optimal spectral window that minimizes scattering while maintaining bright enough signals for high-quality imaging.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides high sensitivity, minimal photoactivation interference, and effective visualization of calcium dynamics in various cell types, including excitable and non-excitable cells, facilitating drug screening and toxicity testing without artifacts.
Implementation Method 1
obtain an optical signal from the red-shifted GECI
Data Source
AI summary
Disclosed are methods and compositions for real-time monitoring cellular calcium ion dynamics by red-shifted genetically encoded indicators under optogenetic control, in which millisecond-timescale of temporal control of optical activation or inactivation and signal recording can be achieved. The methods include artifact-free functional imaging in conjunction with optogenetic tools for studying cellular physiology, signal transduction and neuronal activity. Thus, all-optical and non-invasive approaches for drug screening, toxicity testing and assessment of cell functions may be provided.