Expression of piRNAs and miRNAs in embryonic mouse ovary cells: dysregulation and apoptosis by exposure to Vinclozolin and MEHP
The early stages of embryonic development are critical for the proper formation of primordial germ cells. This process is tightly regulated by different cellular signals. Among others, small non-coding RNAs (sncRNAs) are involved in the regulation of these signals to carry out the embryonic development of germ cell linage. We analyzed the expression profiles of piRNAs and miRNAs after maternal exposure of embryos, during the first 13.5 days post-coitum, to two different endocrine disruptors (EDs) chemicals: vinclozolin and the main metabolite of phthalates (MEHP), in three successive generations after exposure only in the first generation. Our results indicate clear alterations in the expression of both piRNAs and miRNAs (including mitochondrial-related), concomitant with an increase in apoptotic cells in the female early folliculogenesis during this stage of development. However, the most drastic changes occur when the effect is generated by the exposure through both paternal and maternal pathways, rather than exclusively through the maternal exposure. Based on these findings, we hypothesize the existence of an "ovarian filtering" mechanism triggered by disruptor exposure and mediated by apoptotic mechanisms regulated by sncRNAs. This system, present only in the female germ cell lineage, could render a decrease in the follicle reserve in the adult life and would function as a defense mechanism to prevent the transmission of deleterious effects to subsequent generations. Overall design: Briefly, a first generation of mice has been crossed, which are considered generation F0. When a successful mating is detected, they are randomly assigned to Control, VZN or MEHP group. From this moment on, they are exposed during the first 13.5 days of gestation to the endocrine disruptor or control. One part of these pregnant female mice was sacrificed at 13.5 dpc to obtain the fetal ovaries by dissection and differentiation of the sexes by gonadal morphology evident at this date of development, the other part of pregnant female mice was withdrawn from exposure to ED and allowed to finish gestation and birth, to analyze the effects of exposure to ED in the following generations, obtaining embryonic ovaries also at 13.5 dpc in each subsequent generation. This process was repeated two more generations to study both the F1 generation (directly exposed during their embryonic period to DEs) and the F2 and F3 (both indirectly exposed to DEs, since only their first- and second-degree female progenitors, respectively, have been exposed). Furthermore, an additional group was made ("-Sy" group or "paternal effect -PA- group")  evaluating the additive effect of the both progenitros (exposed to the same DE and dose).