NLG-1 GRASP labels specific synapses between PHB sensory neurons and AVA interneurons. (A) Schematic diagram of NLG-1 GRASP, which uses split GFP to label synapses formed correctly between pre- and postsynaptic neurons. (B) If a neurite fails to identify the correct partner, NLG-1 GRASP will not reconstitute. (C) The PHB sensory neurons form synapses with the AVA interneurons in the preanal ganglion (one neuron from each pair is depicted for simplicity). (D) Schematic of an electron micrograph representing the preanal ganglion in cross section from a gravid adult, displaying PHB neurons (red) and their primary postsynaptic partners AVA (blue) and PVC (gray) (adapted from ). (E,F) Schematic (E) and micrograph (F) of the NLG-1 GRASP marker labeling synapses between PHB and AVA neurons. The signal in the dorsal region is gut autofluorescence. (G,H) Schematic (G) and micrograph (H) of mCherry-labeled PHB and AVA neurites in contact. (I,J) Schematic (I) and micrograph (J) of merged image. White boxes indicate the region of neurite overlap. Yellow scale bar: 2 μm.