Adapting and optimizing GCaMP8f for use in Caenorhabditis elegans

Improved genetically-encoded calcium indicators (GECIs) are essential for capturing intracellular dynamics of both muscle and neurons. A novel set of GECIs with ultra-fast kinetics and high sensitivity was recently reported by Zhang et al. (Nature, 2023). While these indicators, called jGCaMP8, were demonstrated to work in Drosophila and mice, data for Caenorhabditis elegans was not reported. Here, we present an optimized plasmid for C. elegans and use this to generate several strains expressing GCaMP8f. Utilizing the myo-2 promoter, we compare pharyngeal muscle activity measured with GCaMP7f and GCaMP8f and find that GCaMP8f is brighter, shows faster kinetics and is less disruptive to the intrinsic contraction dynamics of the pharynx. Additionally, we validate its application for detecting neuronal activity in touch receptor neurons which reveals robust calcium transients at 25 ms time resolution. As such, we establish GCaMP8f as a potent tool for C. elegans research which is capable of extracting fast calcium dynamics at very low magnifications across multiple cell types.