Exposure to 9-cis retinoic acid induces penis and vas deferens development in the female rock shell, Thais clavigera

To clarify how tributyltin (TBT) and triphenyltin (TPT) interact with the retinoid X receptor (RXR) to induce growth of male sex organs in female gastropods, we treated female rock shells (Thais clavigera) with three different concentrations (0.1, 1, or 5 μg/g wet wt) of 9-cis-retinoic acid (9CRA) or with a single concentration (1 μg/g wet wt) of TBT, TPT, or fetal bovine serum (as a control). The effects of each treatment were measured as the incidence of imposex, the length of the penis-like structure, and the vas deferens sequence (VDS) index. 9CRA induced imposex in a dose-dependent manner; imposex incidence was significantly higher in the rock shells that received 1 (P < 0.05) or 5 μg (P < 0.001) 9CRA than in the controls. After 1 month, the rock shells treated with 5 μg 9CRA exhibited substantial growth of the penis-like structure that was not as evident in the other treated shells. The length of the structure differed between the 0.1- and 5-μg 9CRA treatment groups (P < 0.05) but not between the 1- and 5-μg 9CRA treatment groups (P > 0.05). Compared with the control, the VDS index increased significantly in the 1- (P < 0.05) and 5-μg (P < 0.001) 9CRA groups. The penis-like structures behind the right tentacle in female rock shells treated with 5 μg 9CRA were essentially the same as the penises and vasa deferentia of normal males and of TBT-treated or TPT-treated imposexed females. These results further support the hypothesis that imposex in gastropods could be mediated by RXR.