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

我们从泰国岩壳中分离出RXR cdna的两个亚型，RXR亚型1（TcRXR-1）和RXR亚型2（TcRXR-2）。TcRXR-1和TcRXR-2的氨基酸序列与其他腹足动物的氨基酸序列高度同源。在使用COS-1细胞的报告基因检测中，这些TcRXR亚型显示出9cra依赖性转录激活。TcRXR-2的转录活性显著低于TcRXR-1，其产物在C结构域的T-box中增加了5个氨基酸。当TcRXR-2的共转染量大于等量时，观察到TcRXR-1的转录活性降低。同时，利用野外种群和实验室暴露三丁基锡（TBT）的雌性样本，对具有雌雄不对称特征的雌性clavigera雄性生殖器（阴茎和输精管）的发育特征进行了组织学观察。本文对野生雌螟输精管形态发生模式的多样性进行了综述。然而，在初始阶段，未成熟的输精管仅在阴茎下方或后面观察到，在阴道口附近未观察到输精管(1)。暴露于tbt的雌性被囊腺（即外阴），这与野生雌性输精管形成的特征不同。综合野外雌性标本和实验室暴露于tbt的雌性标本的观察结果，提出clavigera输精管序列（VDS）指数为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.