The Influnce Of Environmental Factors On The Active Level Of TEs In Zebrafish

Over the past decade, more and more attention has been put on epigenetics. The researchers seems been more identify with the point of view that there is interaction existed between environment and genome. However, the understanding of interaction mechanisms between environment and genome is still rather vague. Found from the 1950s, transposon had been considered as useless junk genome sequences during the first few decades. However, as more and more species whole-genome sequencing results were revealed, it was found transposon is an important component of the most biological genomes and plays an important role in the genome evolution and function. It seems that many organism genomes have active transposons. Thus, the biological activity organism is likely to achieve response from the activity of these transposons changed by the environment. Namely, changes in the environment affect the activity of transposons, regulatting the transposition of transposon, thus generating new variation, adapting to the new external environment. However, the existing studies about the environmental impact on the activity of transposons are rarely reported. The transposons of nine kinds of bony fish genome was annotated through bioinformatics, comparative analysed between species. The potential active transposons was tapped. On this basis, zebrafish was used as experimental animal to analysis the expression characteristics of temporal and spatial of the representative DNA and RNA transposons, and to study the impacts of the environmental pollutants including organic dioxin (TCDD) and heavy metals on the activity of these transposons.In this study, it includes:1. Using RepeatModeler, LTRharvest, MGEScan-nonLTR and some other softwares to do identification and classification analyses on the transposons of the nine teleost genome through bioinformatics methods. Finally, the false positive ones was screened out.The results showed that the distribution of type Ⅰ and Ⅱ transposons in nine teleost genomes are very rich, and there are significant differences between the amplification of different species, which are certain associated with the differences in genome size:the larger the genome bony fish is, the identified proportion of the transposons is often greater, such as Coelacanth (2700Mb) 41.69%, zebrafish (1330Mb) 54.96%; in the genome of smaller species, the proportion of transposon is less, such as tetraodon (347Mb) 5.89%,fugu (381Mb) 2.94%. The differentiation of transposon family is also extremely rich. Almost all known bony fish transposon families were identified in nine teleost fish.2. We identified the suspected active transposons including:Tc-a, Tc-b, Tc-c, Tc-d, Tc-e, ZB-ERV-1, ZB-ERV-2, L1-323 and L1-23 sequence, synthesizing primers for real-time PCR. The early development eggs of zebrafish including:0.75hpf,2hpf,3hpf,6hpf,15hpf,24hpf and 48hpf embryo were collected and then extracted total RNA, reversed transcription cDNA.12 month-old adult zebrafish were dissected to take out the heart, brain, muscle, liver, testes and ovaries, which were used to reverse RNA extraction to cDNA. Then we do researchs on the change and transposon differential of transposons mRNA levels expressed in zebrafish early development stages and zebrafish tissues by using the above primers. The results showed that: the mRNA DNA transposons (except Tc-d) expression in the early development stages of zebrafish embryos is not detected until 3hpf.The mRNA DNA transposons expression shown the first decline after an upward trend, while RNA transposons shown a consistent upward trend. To the tissue samples, the mRNA expression of RNA and DNA transposons in the brain and heart were significantly higher than the other tissues. What is more the mRNA expression level in testis is the lowest of all tissues.3.To investergate the interaction between environment and the activity of transposons,the 2hpf zebrafish embryos were exploured within 5nM TCDD to introduce for two hours, then changed with normal culture medium until 72hpf.The embryos were collected to extract RNA used for Reversing transcription cDNA. A DMSO control group were designed.The 0.5 hpf zebrafish eggs were exploured to a concentration of 5μmol/L Cu2+ and 30μmol/L Cd2+for 24h,then cultured with fresh E3 solution till 72hpf. RNA was extracted to reverse transcription to cDNA which were used to do real-time quantitity fluorescent PCR, to research on the influence of the environmental pollutants including dioxins(TCDD) and heavy metals on the mRNA levels of transposons in organism genome respectively.The results showed that overall TCDD inhibited the mRNA expression of transposons (except ZB-ERV-2) by a certain extent,besides four DNA transposons and one RNA transposon were significantly inhibited. The mRNA expression of ZB-ERV-2 after treated were significantly upregulated. After exposured to heavy metals Cu, the transposon expression level was generally raised except that the ZB-ERV-1 and Tc-b was significantly suppressed. The exploure of Cd2+ made the TC transposons activity generally raised, the same with Cu, but just suppressed the three RNA transposons except LI-323 which was significantly upregulated.Overall, this study annotated the transposon distributions of nine bony fish genomes and comparatively analysed different species which revealed the difference of transposable groups in nine kinds of bony fish genome, and systematically studied the spatiotemporal expression profiles of nine suspected active transposons in the model organism zebrafish. The influences of environmental factors including heavy metal and TCDD exposure on transposon activity of early zebrafish embryos were analysed. The results reveal the distribution and compositional characteristics of the transposons in bony fish genomes which is benefical to provides important reference for understanding the evolutionary relationships of bony fish, reveals the possible molecular mechanisms by which changes in the environment affect the stability of the genome at the same time.