Stress induced plasticity of the nervous system allows animals to adapt to changing environments by modulating their behavior. We are studying the nervous system rewiring in response to environmental cues by investigating the hibernation-like alternative diapause state of C. elegans, the dauer state. In adverse environmental conditions, mainly starvation, population density and high temperature, C. elegans larvae molt into dauer, which not only show altered morphology, but also show a remarkably altered responsiveness to various environmental cues and strikingly different locomotory behavior. However, the neuronal circuit responsible for these altered behaviors and the molecular mechanism responsible for the circuit remodelling is poorly understood.
We focused our study on innexin (inx) genes, which encode the functional units of invertebrate electrical synapses. In a screen, using fosmid-based fluorescent reporter transgenes, for neuronally expressed inx genes that show altered expression in dauer, we have identified the cellular specificity of inx-6 expression is altered in dauer. In replete condition, inx-6 is only expressed in pharynx throughout life. In dauer, inx-6 expression is additionally turned on in the glutametergic interneuron pair AIB, which regulates locomotion during chemotaxis and odortaxis, by promoting reversals and turns. Furthermore, the inx-6 expression in AIB is reversible. As animals recover from dauer stage, inx-6 expression disappears from AIB. Another diapause stage, the starvation-induced L1-diapause, shows similar plasticity of inx-6 expression in AIB. Using a temperature sensitive inx-6(rr5) allele, we identified that INX-6 activity is required for nictation, a dauer specific dispersal behavior that is also conserved in parasitic nematodes. We also observed that the loss of INX-6 activity and similarly ablation of AIB affects locomotion speed and locomotory quiescence, specifically in dauer. I will present our data on the molecular composition of the INX-6-synapses in dauer-AIB and preliminary results en route to identifying the synaptic partners of dauer-AIB for INX-6-mediated synapses. I will also present our data on the transcriptional control of the inx-6 expression plasticity in the dauer nervous system that provides cellular specificity and also integrates environmental cues. Our studies provide insights into the process of stress induced nervous system plasticity at different levels of gene regulation, circuits and behaviors. .
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