Fig. 1.

zyx-1 mutants lack PLM mechanosensory synapses. (A) Schematic depiction of the touch neuron circuit in C. elegans. Two PLM neurons are located on the left (PLML) and right (PLMR) side of the tail ganglia, and each sends out a process anteriorly and branch into the VNC, where they form a large synaptic varicosity. Two ALM neurons are located on the left (ALML) and right (ALMR) side in the mid-body, and each extends a process anteriorly and branch into the nerve ring. PVM is located on the left side in the posterior and extends a single process to the VNC, where it turns and extends far anteriorly. AVM is located on the right side in the anterior and extends a single process to the VNC, where it turns anteriorly and extends to the nerve ring. Our studies focus on the PLM branches and synapses found in the boxed region, as shown in B. (B) Morphology and presynaptic specializations of PLM neurons visualized with cytosolic mRFP and GFP::RAB-3 expressed under the mec-7 promoter. Confocal images of wild-type animals revealed the two PLM synaptic varicosities labeled by GFP::RAB-3 in the VNC (arrows). By contrast, most zyx-1 young adults lacked PLM synapses; rather, the GFP::RAB-3 signal accumulated as puncta in the PLM processes, forming a beads-on-a-thread-like pattern (arrowheads). Occasionally, PLM synapses were observed in zyx-1; however, these usually were of reduced size and GFP::RAB-3 intensity (arrow). The morphology of the PVM neuron was not affected in zyx-1 mutants (asterisks indicate the PVM cell body). Strains used were NM3361 and NM3410. (C) zyx-1 mutants have otherwise grossly normal synaptic structures. Wild-type and zyx-1(gk190) mutant animals were fixed, permeabilized and immunostained for the synaptic vesicle-associated protein RAB-3 and the presynaptic active zone protein UNC-10. No significant differences were observed between wild-type and zyx-1 animals in the nerve ring (NR), VNC, DNC or in the head cholinergic SAB motor neurons. Strains used were N2 and VC299. Scale bars: 20 μm.