Induction mechanism of imposex caused by organotin compounds in gastropods : elucidation of involvement of the retinoid X receptor

我们在岩壳Thais clavigera中分离了RXR cDNA的两种亚型，RXR亚型1（TcRXR-1）和RXR亚型2（TcRXR-2）。推测的TcRXR-1和TcRXR-2的氨基酸序列与其它腹足类高度同源。这些TcRXR亚型显示9cRA依赖的转录激活在报告基因测定使用COS-1细胞。TcRXR-2的转录活性明显低于TcRXR-1，当TcRXR-2与TcRXR-1共转染时，TcRXR-1的转录活性明显降低。同时，还对雌性黑胸天蛾雄性生殖器（阴茎和输精管）的发育特征进行了研究。在实验室中，使用野生种群和接触三丁基锡（TBT）的雌性动物的标本对Clavigera进行了组织学检查。观察到野生雌性红腹锦鸡输精管的形态发生具有多样性。clavigera，并总结了特征。然而，在初始阶段，未成熟的输精管仅在阴茎下方或后方观察到，而在阴道口附近没有观察到输精管（即，例如，外阴），这与野生雌虫输精管形成的特征不同。结合野生雌虫和实验室暴露雌虫的观察结果，提出了T。clavigera被提议作为VDS 1 - 6。

We isolated two isoforms of RXR cDNAs, RXR isoform 1(TcRXR-1) and RXR isoform 2(TcRXR-2), in the rock shell Thais clavigera. The deduced amino acid sequences of TcRXR-1 and TcRXR-2 are highly homologous with those of other gastropods. These TcRXR isoforms displayed 9cRA-dependent activation of transcription in a reporter gene assay using COS-1 cells. The transcriptional activity of TcRXR-2, the product of which has five additional amino acids in the T-box of the C domain, was significantly lower than that of TcRXR-1.Decreases of the transcriptional activity by TcRXR-1 were observed when more than equal amount of TcRXR-2 was existed in a co-transfection assay. Meanwhile, the characteristics of the development of male genitalia(penis and vas deferens) in imposex-exhibiting female T. clavigera, were histologically examined using specimens from a wild population and tributyltin(TBT)-exposed females in the laboratory. A variety of vas deferens morphogenesis patterns were observed in wild female T. clavigera, and the characteristics were summarised. The immature vas deferens at an initial stage, however, was only observed beneath or behind the penis, and no vas deferens was observed close to the vaginal opening(i. e., vulva) of the capsule gland in TBT-exposed females, which was different from the characteristics of vas deferens formation observed in wild females. Taking into consideration both the observed results from wild female specimens and from TBT-exposed females in the laboratory, the vas deferens sequence(VDS) index for T. clavigera was proposed as VDS 1-6.