The Interaction Of Radiation-induced Bystander Effects And Adaptive Responses Mediated By Volatile Pheromones In Caenorhabditis Elegans

Radiation-induced bystander effects(RIBE)and radio-adaptive responses(RAR)are two canonical non-targeted radiation effects.The RIBE refer to the phenomenon that irradiated cells can induce their neighboring cells to produce the same radiation responses by releasing some signal factors.The discovery and study of RIBE expands the traditional dogma of radiation biology,and also has an important impact on low-dose radiation risk assessment,protection and radiotherapy.Researches into radiation-induced bystander effects are mainly carried out at the cellular level,and gradually extend to the three-dimensional tissue and organismal levels.Recently,RIBE between individuals have received extensive attentions,and definite evidences about inter-organism RIBE have been obtained in rainbow trout,zebrafish,Caenorhabditis elegans(C.elegans)and other animal models,suggesting that the radiation effects can also be amplified in a cascade manner at the population or ecological level.However,the current researches mainly focus on water-soluble bystander signaling molecules in the liquid environment,and there is no report about RIBE mediated by volatile signals between individuals.Considering the important roles of volatile signals in population communication,we here studied the interaction between RIBE and RAR mediated by volatile signals and the underlying mechanisms using the model organism C.elegans.The main research achievements are as follows:1.Establishment of the co-culture system for volatile signal communication between C.elegansIn order to ensure that only volatile signal communication occurs between worms,we established a bottom-top layout of co-culture experimental system.In the experimental system,some worms were cultured in the bottom culture dish,some worms were cultured in the top culture dish,and the bottom and top culture dishes(without covers)were sealed by paraffin film face to face to form a closed room.In this closed room,the worms in bottom and top dishes have no direct physical contact and can only communicate each other through volatile signals.In this experiment,the bottom worms were usually used as a radiation group and the top worms as bystander group.The experimental system is definite and simple,and also allows the combination and separation of the hit and bystander worms at various time points.2.Induction of inter-worm RIBE and evidence of a novel volatile pheromoneIn this study,the embryonic lethal ratio of top worms was used as the checking endpoint,and the effects of irradiated bottom worms on top worms were investigated.It was shown that various doses of y-irradiation made no difference to the embryonic lethality of top worms.However,when the top worms were also exposed to?-irradiation,the irradiation of bottom worms significantly reduced the embryonic lethal ratio of top worms irradiated,exhibiting a significant radiation adaptive response.It is the first time to demonstrate the interaction between RIBE and RAR between individual worms.Our further study showed:1)Worms only at the L3 stage could produce the volatile bystander signals during 10 hours post-irradiation;2)The volatile bystander signals initiated the RAR through DNA damage response(DDR)by targeting proliferating mitotic cells in the distal zone of gonad;3)The production of the volatile bystander signals depended on the biosynthesis and chemosensory neurons of water-soluble ascarosides;4)The volatile bystander pheromone was a novel worm pheromone.3.Heat-induced production of volatile bystander signals for RAR in top wormsIn order to further confirm the broad-spectrum induction of the novel volatile pheromone in worms,the bottom worms were subjected to heat stress,whereas the top worms were still y-irradiated.It was shown that the heat shock of bottom worms likewise enhanced the radio-resistance in top worms,together with the same RAR by the dense culture,indicating the broad-spectrum induction of the novel volatile pheromone.Our further study showed:1)Heat stress could produce volatile bystander signals in the worms at L2,L3,L4 and adult stages;2)The volatile bystander signals could also initiate the RAR in top worms through DDR by targeting the mitotic cells and meiotic cells;4)The production of volatile bystander signals were regulated by AFD and HSF-1,rather than by the ascarosides.4.Comparative analysis of responses and production of volatile bystander signals induce by ?-irradiation and heat stressThe above experiments presented the evidence of a novel volatile pheromone(s),but there is no suitable method for determining their chemical composition.To further explore the metabolic characteristics of the novel pheromone,and eventually find suitable assay and analysis methods,we analyzed comparatively the biological pathways involved in the responses and prodcution of volatile signals induced by by?-irrradiation and heat stress.The clues included 1)The production of volatile bystander signals by y-irradiation and heat stress depends on different upstream biological processes;2)The productin of volatile bystander signals by ?-irradiation and heat stress occurred at different developmental stages of worms;3)The targets of volatile bystander signals induced by y-irradiation and heat stress in the gonads were different.It was speculated:1)y-irradiation and heat stress may produce two distinct types of volatile pheromones,or mixtures with the same components but changed proportions;2)The production of volatile pheromone(s)induced by y-irradiation and heat may be closely related to neural systems of worms.