jGCaMP8 Variants with Improved Expression for <i>Drosophila</i>

The jGCaMP8f/m/s suite of sensors were developed by screening variants in primary culture of mammalian neurons. Although testing in Drosophila showed these sensors also had significant performance improvements in this system, expression levels were consistently lower than jGCaMP7 sensors. In creating the v8 sensors a short (30-amino acid) N-terminal sequence derived from the pRSET bacterial expression vector, thought to be inconsequential, was removed and had no discernible impact in mammalian culture or rodent in vivo work. Adding back the RSET sequence to the jGCaMP8 sensors returned expression and baseline brightness to the level of the jGCaMP7 sensors, while retaining the fast kinetics and high signal-to-noise ratio characteristic of the 8 series in vivo. Based on these observations, we encourage investigators working with jGCaMP8 in Drosophila to use the RSET-restored versions now available at the Bloomington Drosophila Stock Center (Stock Numbers 605071 through 605088), and at Addgene (Plasmid Numbers 218862 through 218867). Investigators encountering low expression in other model systems should consider making this modification in their system.