Estrogenic environmental contaminants alter the mRNA abundance profiles of genes involved in gonadal differentiation of the American bullfrog

摘要

Wildlife and human populations are exposed to anthropogenic mixtures of chemicals in the environment that may adversely influence normal reproductive function and development We determined the effects of exposure to estrogenic chemicals and wastewater effluent (WWE) on developing gonads of the American bullfrog, Rana (Lithobates) catesbeiana, a species whose widespread distribution make it an ideal model for environmental monitoring of endocrine effects of chemical contaminants. Premetamorphic bullfrog tadpoles were exposed to treatment vehicle, 17β-estradiol (E_2; 10~(-9)M) or 4-tert-octylphenol (OP; 10~(-9)M,10~(-8)M, and 10~(-7)M). Additionally, gonadal differentiation was evaluated in bullfrog tadpoles from a WWE-containing site versus those from a reference location receiving no WWE. In both studies, phenotypic sex, steroidogenic factor-1 (nr5a1), and aroma-tase (cyp19a1) Mrna levels using quantitative real-time PCR were determined. Exposure to E_2 or OP did not alter sex ratios. In controls, both nr5a1 and cyp19a1 transcript levels exhibited sexual dimorphism, with males demonstrating higher levels of nr5a1 and females greater abundance of cyp 19a1. However, E_2 exposure increased cyp19al Mrna abundance in testes and decreased levels in ovaries, eliminating the sexual dimorphism observed in controls. E_2-exposed males exhibited increased nr5a1 transcript levels in the testes compared to controls, while females demonstrated no E_2 effect OP treatment had no effect on female cyp19a1 Mrna abundance, but exposure to 10~(-7) M OP increased testicular transcript levels. Treatment with 10~(-9) and 10~(-8) M OP, but not 10~(-7) M, resulted in decreased abundance of nr5al transcript in both ovaries and testes. Animals from the field had sexually dimorphic gonadal levels of cyp 19a J, but both sexes from the WWE site exhibited elevated cyp19a1 transcript abundance compared to the reference location. Individual chemical compounds and anthropogenic wastewater effluent dispersed within the environment influence the levels of gonadal Mrna encoding key proteins involved in gonadal differentiation.