Environmentally relevant concentrations of selenite trigger reproductive toxicity by affecting oocyte development and promoting larval apoptosis

As a trace element, selenium (Se) has been widely added to food to maintain the physiological homeostasis of the organism. The adverse effects of Se on the reproduction of zebrafish have been investigated, however, the effects of Se on the maturation and apoptosis of zebrafish oocytes remain unclear. In this study, zebrafish embryos (2 h post fertilization, hpf) were exposed to 0, 12.5, 25, 50, and 100 mu g Se/L for 120 days. The results demonstrated that exposure to selenite decreased the gonad-somatic index (GSI) and cumulative production of eggs, inhibited oocyte maturation (OM), and increased oocyte apoptosis in females. Exposure to selenite decreased the contents of sex hormones (E2) in the serum and increased the levels of reactive oxygen species (ROS) and cyclic adenosine monophosphate (cAMP) in the ovary. Furthermore, exposure to selenite downregulated the transcription level of genes on the HPG axis, decreased the phosphorylation level of CyclinB and the protein content of cAMP-dependent protein kinase (Pka), and upregulated the expression of genes (eif2s1a and chop) and proteins (Grp78, Chop) related to endoplasmic reticulum stress (ERS) and apoptosis. Moreover, maternal exposure to selenite resulted in the apoptosis of offspring and upregulated the content of ROS and the transcription level of genes related to ERS and apoptosis.