The vab-1/Eph receptor and ephrins efn-1 and efn-4 are required for C. elegans chemosensory and thermosensory circuit assembly and function.

backgroundThe nematode Caenorhabditis elegans displays many distinct behaviors, making it an ideal system to understand the relationship between genes, cells, and behavioral output. In C. elegans, thermal information is primarily detected by the AFD sensory neurons, with minor input from the AWC neurons. Similarly, ionic solutes such as sodium chloride are detected by the ASE chemosensory neurons. Both sensory neuron pairs synapse primarily onto the AIY interneurons.

resultsWe show that AIYL/R ventral contact is mediated via the ephrin gene efn-1 in a linear genetic pathway with vab-1. In addition, we show that this activity requires both a VAB-1 kinase-dependent and a kinase independent function. We also show that efn-4 is required for AFD neuron axon extension, and that this strongly correlates with AIY neuron morphology. ASE morphology, however, does not require efn-4 function. In addition, efn-4 is required, in part, for normal synaptic vesicle cluster count in both AFD and ASEL neurons. Finally, we demonstrate that efn-4 is required for normal thermotaxis behavior, and to a lesser degree, salt-dependent chemotaxis, while vab-1 and efn-1 also contribute to normal thermosensory function, albeit to a lesser degree than efn-4.

conclusionsThese data illustrate that left-right circuit connectivity, between the left-right thermosensory neuron pair and/or the left-right first layer interneuron pair, may be required for normal thermotactic responses. These data also highlight the importance of EphRs and ephrins in multiple aspects of sensory circuit assembly and function and suggest that efn-4 may coordinate thermosensory circuit assembly. CLINICAL TRIAL NUMBER: Not applicable.