The accumulation of Microcystin-LR in the gonads of Pelophylax nigromaculatus during the reproductive periods induces reproductive endocrine disorders in their offspring

Microcystin-LR's reproductive (reproductive and non-reproductive periods) and transgenerational toxicity in amphibians remains poorly understood. Adult Pelophylax nigromaculatus in reproductive and non-reproductive periods were exposed to MC-LR to investigate whether there are differences in the effects of MC-LR on reproductive endocrinology between reproductive and non-reproductive periods of amphibians. Furthermore, cross-mating experiments between MC-LR-exposed and non-exposed frogs in reproductive periods were conducted to explore transgenerational effects. Compared to P. nigromaculatus without MC-LR exposure, exposure to MC-LR resulted in an increase in testosterone synthesis levels and a decrease in estradiol synthesis levels during the reproductive period, but a decrease in testosterone synthesis levels and an increase in estradiol synthesis levels during the non-reproductive period. High lipid contents in the gonads during the reproductive period substantially enriched MC-LR, increasing DNA damage and methylation levels. This may be the reason for the observed opposite trend in sex hormone synthesis levels compared to the non-reproductive period. Additionally, the hypothalamic-pituitary-gonadal-liver axis in F1 tadpoles was disrupted, leading to gonadal dysgenesis, particularly in the ovaries. The observed transgenerational reproductive toxicity may be attributed to decreased gamete quality, transgenerational transfer of MC-LR, and increased DNA methylation level. This study provides novel insights into the differential reproductive endocrine disruption effects of MC-LR during different periods and highlights its transgenerational reproductive toxicity for the first time, underscoring the need for further research on MC-LR's impact on amphibian population dynamics.