A modular system to label endogenous presynaptic proteins using split fluorophores in <i>Caenorhabditis elegans</i>

Visualizing the subcellular localization of presynaptic proteins with fluorescent proteins is a powerful tool to dissect the genetic and molecular mechanisms underlying synapse formation and patterning in live animals. Here, we utilize split green and red fluorescent proteins to visualize the localization of endogenously expressed presynaptic proteins at a single-neuron resolution in Caenorhabditis elegans. By using CRISPR/Cas9 genome editing, we generated a collection of C. elegans strains in which endogenously expressed presynaptic proteins (RAB-3/Rab3, SNG-1/Synaptogyrin, CLA-1/Piccolo, SYD-2/Liprin-α, UNC-10/RIM, RIMB-1/RIM-BP, and ELKS-1/ELKS) are tagged with tandem repeats of GFP11 and/or wrmScarlet11. We show that the expression of GFP1-10 and wrmScarlet1-10 under neuron-specific promoters can robustly label presynaptic proteins in different neuron types. We believe that the combination of our knock-in strains and GFP1-10 and wrmScarlet1-10 plasmids is a versatile modular system useful for neuroscientists to examine the localization of endogenous presynaptic proteins in any neuron type in C. elegans.