Epigenetic Studies On The Influence Of Thermal Acclimation On Zebrafish Development

The biological phenotypes are co-determined by genetic and environmental factors.Environmental temperature affects important biological processes including development,growth,reproduction,movement and others.Extreme temperatures are expected to be on rising due to the global climate change.Fishes live in water,the change of water temperature has great influence on the fish's behaviors,physiological and biochemical activities.In addition,Extreme temperatures cause significant losses to the aquaculture industry.It is important to study the effects of temperature on fish.Zebrafish as an important aquatic model animal which has very much completed genome information is a suitable subject for transcriptome and DNA methylation studies.In recent years,study on zebrafish regulatory network at low temperature has made great strides,make it a perfect candidate for studies on the effects of environmental temperature on fish.Previous works on the effects of extreme temperature on the zebrafish had been mainly focused on larval and adult stages without asking questions on how long the effects could last.It has been known that environmental factors often have long-lasting effects on the behavior of organisms and even affect the survival of their offsprings.Does zebrafish have a temperature acclimation mechanism? What is the mechanism of longterm persistence of temperature acclimation in zebrafish? Whether the effects of low temperature acclimation can be inherited? In order to solve these questions,we designed three experiments.First,we investigated temperature acclimation of zebrafish cells.The cultured ZF4 cells were subjected to short-term and long-term low temperature acclimation.MeDIP-seq was performed to reveal a genomewide methylation profiles.Our data showed that DNA methylation level of whole genome increased after a short-term low temperature acclimation and decreased after a long-term low temperature acclimation.It is interesting that the genes involved in the folate metabolic pathway were significantly hypomethylated after short-term cold acclimation,which was in contrast to the global increase of the initial DNA methylation level.In addition,methylation changes of genes involved in multiple cold responsive biological processes,such as anti-oxidant system,apoptosis,development,chromatin modifying and immune system were detected.Our data indicated the involvement of DNA methylation in cellular response to coldstress.Second,in order to study the mechanism of long-term persistence of temperature acclimation in zebrafish,the fertilized eggs of zebrafish were incubated until hatching at control temperature?27oC,TE27?or at nearly the extremes of normal development,?22 oC or 32 oC,TE22 or TE32?,andraised them at the normal temperature?27oC?for 8 months.The methylation level in the muscle tissue of adult zebrafish was examined by bisulfite-seq method.By analyzing the methylation status of the protein coding genes,we found that the gene bodies from the TE32 group was slightly higher than those of the TE22 and TE27 goups,while the upstream and downstream regions of the genes an opposite trend of methylation pattern was detected.Methykit analysis revealed that TE22 and TE32 showed greater numbers of differentially methylated CpGs?DMCs?sites in relative to the TE27 group.The genes associated with the DMCs are involved in functions as wound healing,ATPase activity,cell-cell adhesion and muscle cell differentiation.Therefore,the methylation status in the muscle tissue of adult zebrafish can be modified by stressful temperature exposures in the early developmental stage.Finally,in order to study whether the effects of temperature acclimation can be inherited to the next generation,we compared the transcriptomes of the ovaries and their offerspring zygotes from zebrafishes acclimated to 22oC?TA22?and those raised at the normal temperature 27 oC acclimation group?TA27?.GO analysis showed that a large number of biological processes related to GPCR signaling pathways were activated.The KEGG analysis showed that the calcium signal pathway was highly enriched.It can be speculated that the GPCR signaling pathway was the first step to perceive the temperature change,which activate the Ca²⁺ signaling pathway.The results suggested that temperature acclimation in the adult fish can be inherited to the next generation.