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

点击翻译按钮获取中文摘要

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.