A modular system to label endogenous presynaptic proteins using split fluorophores in C. elegans

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, CLA-1/Piccolo, SYD-2/Liprin-α, UNC-10/RIM and ELKS-1/ELKS) are tagged with tandem repeats of GFP ₁₁ and/or wrmScarlet ₁₁ . We show that the expression of wrmScarlet _1-10 and GFP _1-10 under neuron-specific promoters can robustly label presynaptic proteins in different neuron types. We believe that combinations of knock-in strains and wrmScarlet _1-10 and GFP _1-10 plasmids are a versatile modular system to examine the localization of endogenous presynaptic proteins in any neuron type.