Evidence for a role of retinoid X-receptor and its endogenous and exogenous agonists in phallic development (=imposex) of Pomacea canaliculata

GIRAUD BILLOUD, MAXIMILIANO.; CASTRO VAZQUEZ, ALFREDO

Buenos Aires

Congreso; SETAC Latin America 11th Biennial Meeting; 2015

Society of environmental toxicology and chemistry

Imposex (= the superimposition of male sexual characters onto females) has been studied in nearly 300 species pertaining to the Vetigastropoda, Neogastropoda and Littorinimorpha (all of them clades of the highly diverse class Gastropoda). However, the Ampullariidae are unique among gastropods in that females show a primordium of the copulatory organs, analogous to the phallic tubercle or clitoris found in other female animals (including vertebrates). This primordial phallic (o copulatory) apparatus grows with age (after sexual maturity) in Pomacea canaliculata (Ampullariidae), but also when it is exposed to tributyltin (TBT) (=imposex). On their part, penises and/or vasa deferentia of non-ampullariid females develop as neoformations in unpredictable places on the right side of the neck. The existence of the well-delimited phallic primordium in P. canaliculata allowed us to study the role of retinoid X receptor (RXR) agonists in the development of imposex. We determined: (1) the effect on phallic growth of 9-cis retinoic acid (9cis-RA), the reported endogenous agonist of RXR, and of TBT, TPT (triphenyltin), reportedly RXR agonists; and (2) the expression of RXR in the phallic apparatus of control, TBT, TPT and 9cis-RA treated females.In the first experiment, 4-month old females received (i.m.) 1 and 2 μg of TBT, TPT or 9cis-RA per g of drained body mass, or the corresponding vehicle (2 μL). The snails were sacrificed 2 and 4 weeks later and the length of the penial sheath (PsL) and the penis (PL) was measured. Also, an ?index of phallic development? was calculated (IPD, similar to the popularly used VDSI, ?vas deferens sequence index?, but adapted to ampullariid anatomy). All studied RXR agonists were effective in increasing PsL, PL and IPD. In the second experiment, the expression of the RXR in the phallic primordium (Western blot) was studied in control, TBT, TPT and 9cis-RA treated females, which showed an increased expression of RXR in response to the agonists, specially with 9cis-RA treatment. It is concluded that endogenous RXR agonists may control phallic development in female P. canaliculata. A possibly similar role should be explored in development of the corresponding primordium in juvenile males and females.