Neuronal activity has been implicated in the establishment and maintenance of appropriate synaptic connections in vertebrate and invertebrate systems. However, the molecular mechanisms by which neuronal activity affects connectivity are poorly understood. To understand this process, we have focused our studies on the PHB phasmid sensory neurons. We have begun to elucidate the pathway by which sodium dodecyl sulfate (SDS) is sensed by the phasmid neurons using a high throughput assay adapted from the method developed by Hilliard and colleagues (Current Biology, 2002). Briefly, SDS is sensed by the PHB neurons, which terminate backward movement via their connections with AVA interneurons. Using this assay, we find that
odr-3/Galphaolf and
tax-2/CNG-channel beta subunit, in addition to previously discovered
tax-4/CNG-channel alpha subunit (Hilliard et al., Current Biology, 2002), are required for SDS chemosensation. To determine if defects in sensory signaling affect sensory synapses, we utilized the split-GFP-based trans-synaptic marker NLG-1 GRASP (Neuroligin-1 GFP Reconstitution Across Synaptic Partners) to visualize synapses between PHBs and AVA interneurons in live animals. Interestingly, we find that neuronal activity is required for maintaining these sensory synapses. Time course experiments indicate that
odr-3/Galphaolf mutant L1s have normal synapses, but synapses are significantly reduced in later larval stages, although phasmid neuron morphology appears to be unaffected. Cell-specific rescue experiments indicate that
odr-3/Galphaolf likely functions in PHB neurons. Subcellular localization of
odr-3/Galphaolf shows localization to the PHB cilia, consistent with a role in sensory signaling being required to maintain synaptic integrity. These results indicate that C. elegans may be a powerful model organism for elucidating the molecular mechanisms by which sensory activity affects synaptic connectivity. Our future goal is to further characterize the mechanism by which sensory activity maintains synapses using molecular genetic and physiological approaches. Funded by NIH (1R01NS087544 to MV at SJSU and NL at UCSF, 5T34GM008253 MARC undergraduate fellowship to CV, 2R25GM071381 RISE undergraduate fellowships to CV and JP), HHMI (SCRIBE 52006312 undergraduate fellowship to BB and KM), and NSF (RUMBA REU 1004350 fellowship to KA and EH).