The molecular mechanisms that regulate the formation and function of glutamate synapses in vivo are not well understood. To identify novel genes important for glutamate synapse function, we performed an RNAi screen using a mechanosensory reflex mediated by ASH glutamatergic sensory neurons called the nose touch response1-3. Expression of light-activated channelrhodopsin in ASH4 enabled us to screen populations of worms using ASH-stimulated, glutamate-dependent locomotor reversals as a behavioral readout. RNAi knockdown of
ver-1 and
ver-4, Vascular Endothelial Growth Factor Receptor homologs2, yielded a specific defect in glutamate-dependent reversal behavior. Loss of function mutants confirmed these RNAi results, and cell-specific rescue experiments showed that both
ver-1 and
ver-4 act cell-autonomously to regulate nose touch behavior. By imaging GLR-1 tagged with both mCherry and pH-sensitive superecliptic pHluorin (SEP::mCherry::GLR-1)6 we found that ver mutants exhibited a preferential loss of cell surface GLR-1. Additionally, we found that blocking endocytosis with
unc-11/AP180 clathrin adaptin mutants, prevents the decrease in cell surface GLR-1 observed in
ver-1 mutants, suggesting that VER-1 acts to promotes plasma membrane levels of GLR-1 downstream of its initial insertion and endocytosis. Mutants lacking the VER ligand PVF-17 exhibited similar defects in plasma membrane GLR-1 levels and related reversal behaviors, suggesting that ligand binding may be required for VER-mediated promotion of glutamate signaling. Interestingly,
pvf-1 and ver mutants underwent faster habituation to nose-touch, suggesting that VER signaling modulates non-associative learning. Together, our data support a model where VERs and their ligand PVF-1 regulate recycling to promote cell surface levels of GLR-1 and associated behaviors. References: 1. Hart, AC., et al. (1995) Nature 378:6552 2. Maricq, AV., et al. (1995) Nature 378:6552 3. Kaplan, JM and Horvitz, HR. (1993) PNAS 90:6 4. Ezcurra, M., et al. (2011) EMBO J 30:1110 5. Popovici, C., et al. (2002) Neurosci. Lett. 329:116 6. Hoerndli, F. J., et al. (2013) Neuron 80:1421 7. Dalpe, G., et al. (2013) Development 140:4020