| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Yukio Niigata University, Institute of Science and Technology, Professor, 自然科学系, 教授 (70134955)
KAJIHARA Hideo Niigata University, Institute of Science and Technology, Associate Professor, 自然科学系, 助教授 (70324001)
NIIMURA Sueo Niigata University, Institute of Science and Technology, Professor, 自然科学系, 教授 (00156027)
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| Research Abstract |
Polychlorinated dibezo-p-dioxins (PCDDs), polychrorinated dibenzofurans (PCDFs) and dioxin-like poly chrorinated dibenzofurans (dioxine-like PCBs), which are generically called as dioxins, are highly toxic and persistent lipophilic substances. These compounds are mainly produced in the process of incineration for industrial waste products or burning on the filled-up land for such products, and then are released into soil and air. These are known to bioaccumulate up the food chain and damage to reproductive activities of higher consumers in food web. Recently, however, it have been reported that the Japanese large field mouse, Apodemus speciosus, which have been regarded as comparatively lower consumer, had the highest accumulation of dioxins among mammals in a food web including higher consumers such as fox and weasel, which means that this species become an effective biomarker for evaluating an effect of dioxins contamination to wildlives. Dioxins cause various biological and toxicolo
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gical responses, typified by teratogenesis, thymic atrophy, severe epithelial disorders, wasting symdrome, tumore promotion, and induction of drug-metabolizing enzymes in experimental animals. Furthermore, the hormonal acts that dioxins exhibit make the endocrine system of animals disrupt and consequently cause abnormal sexual gland and decreased sperm counts.
To clarify physiological and ecological effects of dioxins exposure on wild populations of A.speciosus, we firstly investigated the relationship between dioxins concentration in soil and its accumulation level in mouse liver, and the relationships between dioxins accumulation in mouse and sperm activity, or sperm counts, in adult male A.speciosus. Next, we analyzed polymorphism and its functional difference in aryl hydrocarbon receptor (AhR) of A.speciosus, which is well known as the receptor of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Mice and soils were collected from seven points ; four points in Niigata prefecture, one in Yamagata prefecture, one in Saitama prefecture, and one in Fukuoka prefecture. No significant correlation found between concentrations of dioxins in soils and dioxin accumulation levels in mice, although dioxin accumulations in mice tended to increase with dioxin concentrations in soils. On the other hand, the sperm activity and sperm count were decreased with dioxin accumulation, in the case except for the highest study site of dioxin contamination. Primary structure of A speciosus AhR was extremely variable. The mutations were concentrated in two regions, i.e. between PAS-A and PAS-B, and transactivation domain. A.speciosus AhR showed high transcriptional activity in response to 3MC. One mutation of Q799 to R in transactivation domain decreased activity. On the other hand, there was no difference in transcriptional activity among mutations in PAS domain.
In conclusion, dioxins may disrupt the endocrine system of A.speciosus and AhR having high intraspecific variation may become an effective molecular marker to evaluate effect of dioxins at population level. Less
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