The Effects Of Parental BPA Exposure On Embryonic Development And Gonad Differentiation In The Offspring Of Rare Minnow Gobiocypris Rarus

Bisphenol A（BPA）is an endocrine disruptor which exists widely in the water environment.Earlier studies have found that parental BPA exposure can affect the sex ratio of G.rarus of offspring,there is a tendency of masculinity of the male offspring after parental G.rarus recovering in water.However,its mechanism of action is not yet clear.In this study,G.rarus was used as the experimental model.G.rarus at 3 months was exposed to 15μg·L^-1 BPA for 60 d,and the offspring（NR:Non-Recovery）were obtained by artificial reproduction.After the exposed parental G.rarus recovering in water for 45 d,we get offspring（R:Recovery）by artificial reproduction.The toxicity of parental BPA exposure to the offspring during embryonic development was evaluated by counting relevant indicators of the offspring during embryonic development.We calculated the sex ratio of offspring and conducted histological examination to explore the effect of parental BPA exposure on gonad development and differentiation of offspring,and we detected sex steroid hormone levels and VTG levels of offspring to study the effects of parental BPA exposure on sex hormone synthesis and VTG synthesis of offspring;we explored the molecular mechanism of parental BPA exposure affecting reproductive development and sex regulation of NR offspring G.rarus by RNA-seq,and we detected the genes regulating reproduction-related genes in offspring R by q RT-PCR to explore the molecular mechanism of BPA on gonadal development and differentiation of offspring after the exposed parental G.rarus recovering in water for 45 d.We compared whether the effects of BPA on embryo development and gonadal differentiation of the offspring can be weakened or eliminated after the exposed parental G.rarus recovering in water through researching on the offspring NR and R.The main results are as follows:1. Parental G.rarus was exposed to 15μg·L^-1 BPA for 60 d,the spawning volume and egg diameter were significantly reduced,and the fertility rate and hatching rate were significantly reduced.The autonomic movement and embryo heart rate,deformity rate,and mortality were significantly increased.These showed that the parental BPA treatment significantly inhibited embryonic development,but the inhibitory of BPA on the embryonic development of the offspring was weakened after parental G.rarus recovering in water.2. Parental G.rarus was exposed to 15μg·L^-1 BPA for 60 d,the larval development of the offspring is promoted,but the promotion is weakened with the development.The NR offspring ovary weight and GSI are significantly increased,but the total number of oocytes is reduced;the effect of BPA on the testis development of offspring was not significant,but its sperm quality decreased;the male sex ratio of offspring increased under parental BPA exposure,indicating that BPA can affect sex differentiation of offspring through parental BPA exposure.3. Parental G.rarus was exposed to 15μg·L^-1 BPA for 60 d,the levels of T and 11-KT in the offspring’s gonads and serum increased,but there was no significant change in the levels of E2 and VTG,which showed that parental BPA exposure disrupts sex steroid hormone synthesis of offspring.But the effect was weakened after parental G.rarus recovering in water for 45 d.4. Transcriptome results showed that parental BPA exposure can affect the gonad differentiation and development process by affecting the offspring’s spermatogenesis,sex hormone synthesis,cell cycle and the expression of genes related to ovarian development,BPA mainly promotes spermatogenesis and regulates the expression of genes related to T and 11-KT synthesis in the gonads.BPA also inhibits the expression of genes related to ovarian development.5. When parental G.rarus recovered in water for 45 d,BPA can still affect the R offspring gonadal differentiation and development by affecting the expression of reproduction-related genes,steroid synthesis-related genes and sex hormone receptor-related genes in the offspring’s gonads.In summary,this study found that parental BPA exposure can inhibit offspring embryonic development and interfere with gonad development and differentiation,and lead to an increase in male sex ratios,but the adverse effects of BPA on offspring is reduced after parental G.rarus recovering in water for 45 d.In addition,we found that parental BPA exposure can regulate the gonad differentiation and development process by affecting the expression of genes related to offspring’s spermatogenesis,sex hormone synthesis and ovarian development.BPA can also affect the synthesis of steroid hormones by interfering with the expression of the steroid synthesis gene and the levels of androgen increased in offspring.The combined action of these genes and sex hormones may lead to masculinization of the offspring.