Evaluation of dioxins contamination to the large field mouse, Apodemus speciosus

多氯二苯并对二恶英（pcdd）、多氯二苯并呋喃（pcdf）和类二恶英多氯二苯并呋喃（类二恶英PCBs），一般称为二恶英，是剧毒和持久性亲脂物质。这些化合物主要是在工业废物焚烧或在工业废物填埋的土地上燃烧过程中产生的，然后释放到土壤和空气中。众所周知，这些物质会在食物链中生物积累，并损害食物链中较高消费者的生殖活动。然而，最近有报道称，日本大田鼠（Apodemus speciosus）是二恶英消费水平相对较低的哺乳动物，其食物网中二恶英积累量最高，包括狐狸和黄鼠狼等高消费动物，这意味着该物种成为评估二恶英污染对野生动物影响的有效生物标志物。在实验动物中，二恶英引起多种生物和毒性反应，典型表现为致畸、胸腺萎缩、严重上皮疾病、消耗综合征、肿瘤促进和诱导药物代谢酶。此外，二恶英所表现出的激素作用使动物内分泌系统紊乱，从而导致性腺异常和精子数量减少。为了阐明戴奥辛暴露对野生白鲟种群的生理和生态影响，我们首先研究了土壤中戴奥辛浓度与小鼠肝脏中戴奥辛积累水平的关系，以及小鼠体内戴奥辛积累与成年雄性白鲟精子活性或精子数量的关系。其次，我们分析了A.speciosus（2,3,7,8-四氯二苯并-对二恶英（TCDD）受体）芳烃受体（AhR）的多态性及其功能差异。从7个点采集小鼠和土壤；新泻县4个，山形县1个，埼玉县1个，福冈县1个。土壤中的二恶英浓度与小鼠体内的二恶英积累水平之间没有发现显著的相关性，尽管小鼠体内的二恶英积累倾向于随着土壤中二恶英浓度的增加而增加。另一方面，精子活性和精子数量随着二恶英的积累而降低，除了二恶英污染最高的研究地点。A speciosus AhR的初级结构变化很大。突变集中在PAS-A和PAS-B之间的两个区域和反活化结构域。A.speciosus AhR对3MC有较高的转录活性。Q799转R的一个突变降低了酶活性。另一方面，PAS结构域突变间的转录活性没有差异。综上所述，二恶英可能会干扰白鲟的内分泌系统，种内AhR的高变异可能成为种群水平上评价二恶英影响的有效分子标记。少

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 … More 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