Endocrine disruptors cause multigenerational and transgenerational epigenetic changes in fish exposed during early life

The inland silverside, Menidia beryllina, is a euryhaline fish and a model
organism in ecotoxicology. We previously showed that exposure to picomolar
(ng/L) levels of endocrine disrupting chemicals (EDCs) can cause a variety
of effects in M. beryllina, from changes in gene expression to phenotypic
alterations. Here we explore the potential for early life exposure to EDCs
to modify the epigenome in silversides, with a focus on multi- and
transgenerational effects. EDCs included contaminants of emerging concern
(the pyrethroid insecticide bifenthrin and the synthetic progestin
levonorgestrel), as well as a commonly detected synthetic estrogen
(ethinylestradiol), and a synthetic androgen (trenbolone) at exposure
levels ranging from 3 to 10 ng/L. In a multigenerational experiment, we
exposed parental silversides to EDCs from fertilization until 21 days post
hatch (dph). Then we assessed DNA methylation patterns for three
generations (F0, F1, and F2) in whole body larval fish using reduced
representation bisulfite sequencing (RRBS). We found significant ( =
0.05) differences in promoter and/or gene body methylation in treatment
fish relative to controls for all EDCs and all generations indicating that
both multigenerational (F1) and transgenerational (F2) effects that were
caused by strict inheritance of DNA methylation alterations and the
dysregulation of epigenetic control mechanisms. Using gene ontology and
pathway analyses, we found enrichment in biological processes and pathways
representative of growth and development, immune function, reproduction,
pigmentation, epigenetic regulation, stress response and repair (including
pathways important in carcinogenesis). Further, we found that a subset of
potentially EDC responsive genes (EDCRGs) were differentially methylated
across all treatments and generations and included hormone receptors,
genes involved in steroidogenesis, prostaglandin synthesis, sexual
development, DNA methylation, protein metabolism and synthesis, cell
signaling, and neurodevelopment. The analysis of EDCRGs provided
additional evidence that differential methylation is inherited by the
offspring of EDC-treated animals, sometimes in the F2 generation that was
never exposed. These findings show that low, environmentally relevant
levels of EDCs can cause altered methylation in genes that are
functionally relevant to impaired phenotypes documented in EDC-exposed
animals and EDC exposure has the potential to affect epigenetic regulation
in fish that have not been directly exposed.