Functional imaging in the zebrafish retinotectal system using RGECO.

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• Genetically encoded calcium indicators (GECIs) are crucial for non-invasive neural activity monitoring.
• Traditional GFPs limit multicolor imaging; red-shifted GECIs like RGECO expand capabilities.
• Previous studies showed RGECO for spontaneous activity, but its response to evoked activity and in vivo performance were unknown.

Purpose of the Study:

• To systematically analyze the performance of red genetically encoded calcium indicators (RGECO) and their presynaptic variants.
• To compare RGECO with existing green indicators like GCaMP.
• To demonstrate in vivo neural activity imaging using RGECO in a zebrafish model.

Main Methods:

• Dissociated hippocampal neurons were used to analyze cytosolic and presynaptically localized RGECO (SyRGECO).
• Performance metrics including dynamic range, signal-to-noise ratio, and kinetics were evaluated.
• In vivo imaging was performed in the zebrafish retinotectal system.

Main Results:

• RGECO demonstrated comparable dynamic range, SNR, and kinetics to GCaMP3, but superior single-action-potential reporting.
• Presynaptically targeted SyRGECO and SyGCaMP3 showed enhanced sensitivity compared to cytosolic forms.
• In vivo imaging in zebrafish confirmed RGECO's ability to report neural activity and enable structural analysis.

Conclusions:

• RGECO is a reliable red GECI for both spontaneous and evoked neural activity.
• Presynaptic targeting enhances GECI sensitivity for detecting neural circuit activity.
• RGECO facilitates multicolor in vivo imaging and functional characterization of neural circuits in zebrafish.