Gene Screening And Preliminary Study On The Neural Pathway Of Hydrosensation In Caenorhabditis Elegans

As a kind of widespread substance on earth, water is an important component in organisms and vital to the survival of all living organisms. Organisms equip with the ability to perceive external and internal environment water level and its changes and translate the stimulations into sensory signals – water sensation(hydrosensation), that are analyzed and integrated in nervous system, and generate proper physiological and behavioral responses accordingly to adapt the environmental changes and keep physiological homeostases and survival.Caenorhabditis elegans is an ideal model organism for the study of the water sensation. In both wild and laboratory cultivation environments, C. elegans lives in the medium containing water film on the surface and moves on the surface with the help of the water tension. If the water film is too thick, it bring a lot of obstacles to worm's movement. If the water film is too thin, worm will lose water and be desiccate to death. So the water content of the surface is important for C. elegans. The nematode can perceive a variety of environmental cues and has complete sensillar organs and nervous system, which make the worm accordingly react to the water as stimulus. However, the molecular mechanism and neural circuit of hydrosensation in C. elegans are not clear.This research designed two behavioral paradigms including 6%- 2% agarose with diffusion model and four-quadrant agarose with equal concentration of Na+ model, which are optimized on the basis of the cylindrical wedge-shaped agar model and four-quadrant agarose model. The optimal paradigms eliminated the interference of sodium as well as other water-soluble ions and made water content to be the only variable. By using optimal paradigms, we verified that wild type N2 strain exhibited hydroavoidance behavior. The study has tested key genes in signal pathway of GPCR- G-protein- DAF-11- cGMP-TAX-2/TAX-4. Furthermore, this pathway working in the neurons with sensory cilia was confirmed.We performed sensory neurons' calcium imaging under the alternative pattern of air and water to search for the neurons which involved in hydrosensation. We found that ASER neuron restored the calcium signal of water stimuli by using specific promoter rescued tax-4 in ASER neuron under the background of tax-4(ks28) mutant, indicating that ASER neuron involved in hydrosensation. However, daf-11 gene was not expressed in ASER neuron. So we performed gene screening to other receptor-like guanylate cyclase which expressed in ASER neuron. Combining with the results of calcium imaging, we identified that gcy-22 was important in the hydrosensation. We also found that ASER neuron restored the calcium signal by using specific promoter rescued gcy-22 in ASER neuron under the background of gcy-22(tm2364) mutant, suggesting that gcy-22 acting on ASER neuron mediated hydroavoidance behavior. Our work presented preliminary study on genes and neural pathway of hydrosensation in C. elegans,which provided a basis to explore integrated neural circuit.