Foetal exposure to the bisphenols BADGE and BPAF impairs meiosis through DNA oxidation in mouse ovaries.

Many endocrine disruptors have been proven to impair the meiotic process which is required for the production of healthy gametes. Bisphenol A is emblematic of such disruptors, as it impairs meiotic prophase I and causes oocyte aneuploidy following in utero exposure. However, the mechanisms underlying these deleterious effects remain poorly understood. Furthermore, the increasing use of BPA alternatives raises concerns for public health. Here, we investigated the effects of foetal exposure to two BPA alternatives, bisphenol A Diglycidyl Ether (BADGE) and bisphenol AF (BPAF), on oogenesis in mice. These compounds delay meiosis initiation, increase the number of MLH1 foci per cell and induce oocyte aneuploidy. We further demonstrate that these defects are accompanied by changes in gene expression in foetal premeiotic germ cells and aberrant mRNA splicing of meiotic genes. We observed an increase in DNA oxidation after exposure to BPA alternatives. Specific induction of oxidative DNA damage during foetal germ cell differentiation causes similar defects during oogenesis, as observed in 8-oxoguanine DNA Glycosylase (OGG1)-deficient mice or after in utero exposure to potassium bromate (KBrO3), an inducer of oxidative DNA damage. The supplementation of BPA alternatives with N-acetylcysteine (NAC) counteracts the effects of bisphenols on meiosis. Together, our results propose oxidative DNA lesion as an event that negatively impacts female meiosis with major consequences on oocyte quality. This could be a common mechanism of action for numerous environmental pro-oxidant pollutants, and its discovery, could lead to reconsider the adverse effect of bisphenol mixtures that are simultaneously present in our environment.

Enod40, a short open reading frame-containing mRNA, induces cytoplasmic localization of a nuclear RNA binding protein in Medicago truncatula.

In eukaryotes, diverse mRNAs containing only short open reading frames (sORF-mRNAs) are induced at specific stages of development. Their mechanisms of action may involve the RNA itself and/or sORF-encoded oligopeptides. Enod40 genes code for highly structured plant sORF-mRNAs involved in root nodule organogenesis. A novel RNA binding protein interacting with the enod40 RNA, MtRBP1 (for Medicago truncatula RNA Binding Protein 1), was identified using a yeast three-hybrid screening. Immunolocalization studies and use of a MtRBP1-DsRed2 fluorescent protein fusion showed that MtRBP1 localized to nuclear speckles in plant cells but was exported into the cytoplasm during nodule development in enod40-expressing cells. Direct involvement of the enod40 RNA in MtRBP1 relocalization into cytoplasmic granules was shown using a transient expression assay. Using a (green fluorescent protein)/MS2 bacteriophage system to tag the enod40 RNA, we detected in vivo colocalization of the enod40 RNA and MtRBP1 in these granules. This in vivo approach to monitor RNA-protein interactions allowed us to demonstrate that cytoplasmic relocalization of nuclear proteins is an RNA-mediated cellular function of a sORF-mRNA.