| Endocrine disrupting chemicals ?EDCs? in aquatic environment could influence the development process of amphibian because of its reproduction and larval development completed in water. The thyroid hormones ?THs? could control amphibian metamorphosis via combining with thyroid hormone receptors ?TRs?. The activation and deactivation process of THs were adjusted by deiodinases ?Dios?. Octylphenol ?OP? was the main degradation products of alkylphenols polyethenoxy ethers. As one of the pollutants in the environment with the characteristics of easy to bioaccumulate and degradation-resistant, OP could produce adverse effects on organisms. Chinese brown frogs ?Rana chensinensis?, a species distributed widely in northern China, belongs to Rana and also has very important medicinal value. R. chensinensis larvae are sensitive to the aquatic environment and the embryonic and post-embryonic development of which were completed mainly in the mountain streams. Easy availability of larval material was widely used as one of the materials in the research about the water environment pollution. The TRa and TR? of R. chensinensis were successfully cloned in the previous experiments of our laboratory and the expression patterns of TRa and TR? were detected in a series of important organs during the metamorphosis.In order to explore whether the effects of OP on growth and development of amphibian larvae via interfering the thyroid function, R. chensinensis tadpoles were considered as experimental animal in this study. The tadpoles at Gosner stage 29 were exposed to 10-8,10-7 and 10-6 mol/L OP until 70% tadpoles completing metamorphosis respectively. The body length and weight of tadpoles were measured exposure for 20 and 40 days, and the developmental times of 70% tadpoles at stages 33,38,43 and 46 were also recorded. In addition, the microstructures of tadpole thyroid gland were observed through tissue section. And OP exposure for 20,30,40 and 50 days, the expressions of Dio2, Dio3, TRa and TR? mRNAs were detected by qRT-PCR in the liver, brain, skin and tail of tadpoles under different OP concentration and exposure times. The main results were as follows:1. OP exposure for 20 d, compared with control, the body length and weight of tadpoles in 10-8 mol/L OP have no significant difference. In 10-7 mol/L OP, the growth of body length was significantly reduced but the weight was not significant difference. The growth of body length was highly significantly reduced and weight was also reduced significantly in 10-6 mol/L OP. Exposure for 40 d, compared with control, the growth of body length in all OP treatments was highly significantly reduced. The increase of weight was not significant in OP treatments except in 10-6 mol/L OP with significant reduction. These results indicated that OP could affect the growth of tadpoles in the dose and time cumulative manner.2. Statistics of tadpole developmental times showed that, OP exposure could delay development of tadpoles. Among them, compared with control, exposed to 10-8 mol/L OP, the developmental lag times of 70% tadpoles at stages 33,38,43, and 46 were not significant difference. In 10-7 mol/L OP, the developmental lag times of 70% tadpoles at stages 33 and 38 were not significant while significant difference at stages 43 and 46. In 10"6 mol/L OP, the developmental lag times of 70% tadpoles at stages 33,38 and 46 were significant difference, and highly significant at stage 43. These results indicated that OP exposure for a long time could delay the development of tadpoles.3. Histological observation showed that compared with the control, OP exposure for 40 d, no obvious structural changes of thyroid were in 10-8 and 10-7 mol/L, while the follicular epithelial cells of thyroid became smaller and the cytoplasm was reduced in 10-6 mol/L. These indicated that OP could affect the structures of thyroid gland.4. QRT-PCR showed that compared with control, In the liver of the tadpoles, the experessions of Dio2 mRNA were upregulated in all OP treatments when exposing for 30 d, while downregulated at 40 and 50 d. The expressions of Dio3 mRNA were upregulated in 10-7 and 10-6 mol/L OP. The expressions of TRa and TR? mRNAs were downregulated in all OP treatments.In the brain, the expressions of Dio2 mRNA were downregulated significantly in all treatments, while the expressions of Dio3 mRNA were upregulated mainly after exposing for 30 d. In addition, in all OP exposure times, the expressions of TRa mRNA were downregulated and the levels of TR? mRNA mainly showed a decreasing trend.In the skin, OP exposure for 20 and 30 d, the expressions of Dio2 mRNA were downregulated while upregulated at 40 and 50 d in all treatments. The expressions of Dio3 mRNA were upregulated exposure for 30,40 and 50 d. The expressions of TRa mRNA were downregulated in all OP treatments, and OP could decrease the levels of TR? mRNA from exposing for 30 d.In the tail, the expressions of Dio2 mRNA mainly showed downward trends in all OP treatments. OP exposure for 30 and 40 d, the expressions of Dio3 mRNA showed upward trends. The expressions of TRa mRNA were downregulated in all OP treatments, and the expressions of TR? mRNA were downregulated at 30 and 40 d.The results showed that OP as a kind of EDCs, could not only influence the activity of THs via disrupting the expressions of Dio2 and Dio3 in the liver, brain, skin and tail, but also affect the function of THs via interfering with the expressions of TRa and TR?, further affect the growth and development, tissue reconstruction and tail degradation of tadpoles. In the present study, with the extension of exposure times in OP treatments, the expressional change trends of TRa and TR? in four tissues of tadpoles were similar with the expressional patterns of TRa and TR? of the tadpoles with the developmental process in control. These indicated that OP just changed the TRa and TR? mRNA levels, but has no expressional patterns effects on the two genes during developmental process of tadpoles. Therefore, low-dose continuous OP exposure only could delay the growth and development of tadpoles, but there is no survival threat to tadpoles. |
PDF Full Text Request