| Tris(1,3-dichloro-2-propyl)phosphate(TDCIPP)is a major substitute for polybrominated diphenyl ethers(PBDEs).The large use of this complex has resulted in its wide distribution in a variaty of aquatic environments,and the aquatic organisms are frequently exposed to the compound.Many previous studies have indicated that TDCIPP might have neurotoxicity and alter motor behaviors in zebrafish(Danio rerio)larvae.These studies mainly focused on acute exposure with high concentrations.However,the effects of TDCIPP of environmental-relevant concentrations on the neurodevelopment in fish remains unknown.In addition,our previous studies showed that the toxicity of TDCIPP of environmental-relevant concentrations could be transferred from parents to the offspring and cause negative effects in the offspring,but the multigenerational effects of TDCIPP of environmental concentrations on zebrafish are still unexplored.Thus,in this study,we used zebrafish as a model,and studied the effects of TDCIPP of environmental concentrations on the neurobehavior of F1 offspring after chronic exposure of parent zebrafish to this compound,as well as the possible mechanism of TDCIPP-induced neurobehavioral changes in the offspring by exploring the DNA methylation changes in the offspring.We also studied the developmental neurotoxicity on5 dpf zebrafish larvae of each generation after exposure for three consecutive generations,and the possible mechanism was explored through chemical and biological analysis.1.Zebrafish embryos were exposed to TDCIPP of environmental concentrations(0,3,30,300 ng/L)for 120 days,and eggs were collected and cultured to 5 dpf in clean water.The contents of TDCIPP in adult zebrafish and eggs,and the motor behaviors of adult zebrafish and the offspring were investigated.The results showed that the growth and development of adult fish were inhibited after environmental-relevant concentrations of TDCIPP exposure,but the neurobehavior was not affected.TDCIPP was accumulated in adult fish and transferred to their offspring,and the growth,development,and the swimming behavior of the offspring were inhibited.The whole genome DNA methylation level was decreased,and the expression of most of neurodevelopmental-related geneswith significant difference in DNA methylation were significantly down-regulated in F1 5dpf larvae(such as slc1a2 b,il1rapl1b,scn1 bb,ric3b,pemt,brinp3 a.1 etc).Validation of DNA methylation revealed increased methylation levels of promoter regions,indicating decreased expression of these genes.Thus,TDCIPP might regulate the expression of neurobehavioral related genes by altering the levels of DNA methylation in larvae,and then inhibited the swimming behavior of larvae.2.The developmental neurotoxicity on 5 dpf zebrafish larvae of each generation was investigated after exposure to 0,3,30 and 300 ng/L TDCIPP for three consecutive generations.Our results showed that the hatching and survival rates were significantly affected in the F1 5 dpf larvae,but were unaffected in neither F2 nor F3 5 dpf larvae.Behavioral measurements showed that exposure to 3 or 300 ng/L TDCIPP significantly decreased the swimming behavior response of F1 5 dpf larvae to both light and dark stimulation.TDCIPP significantly increased expression of the neural marker genes ngn1 and axon-related genes(?1-tubulin,netrin1 b and zn5)in F1 larvae.In addition,correlation analysis showed that the inhibition of swimming speed was significantly correlated with the expression of genes ngn1,?1-tublin and zn5,which suggested that the disturbance on nerve development might lead to the abnormal behaviors in F1 larvae.For F2 larvae,only 300 ng/L TDCIPP caused a significant decrease in swimming speed under light stimulation,and resulted in a significant decrease in the expression of genes related to nerve development and regeneration(elvl3,gap43,gfap,and shha),however,there was no significant correlation between the inhibition of behaviors and the altered expressions of genes in F2 larvae.For F3 larvae,TDCIPP exposure no longer had a significant effect on motor behavior.Taken together,our results showed that the multi-generational exposure to TDCIPP at environmental concentrations had neurodevelopmental toxicity to the offspring larvae,which exhibited changes in motor behavior and/or expressions of neurodevelopmental related genes,but the toxic effects decreased with the increase of number of generations being exposed.The contents of TDCIPP in adult zebrafish and eggs showed a decreasing trend with the increase of exposure algebra,which may be one of the main reasons for the decrease of toxicity. |
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