TCDD-induced multi- and transgenerational changes in the methylome of male zebrafish gonads

Abstract

The legacy endocrine disrupting chemical and aryl hydrocarbon receptor agonist, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is produced as a byproduct of industrial processes and causes adverse health effects ranging from skin irritation to cancer. TCDD endpoints are also observed in subsequent, unexposed generations; however, the mechanisms of these multi- and transgenerational effects are unknown. We hypothesized an epigenetic mechanism, specifically DNA methylation for the transgenerational, male-mediated reproductive effects of developmental TCDD exposure. Using whole genome bisulfite sequencing, we evaluated DNA methylation changes in three generations of zebrafish, the first of which was exposed to TCDD during sexual development at 50 ppt for 1 h at both 3- and 7-week post-fertilization. We discovered that TCDD induces multi- and transgenerational methylomic changes in testicular tissue from zebrafish with decreased reproductive capacity, but most significantly in the indirectly exposed F1 generation. In comparing differentially methylated genes to concurrent transcriptomic changes, we identified several genes and pathways through which transgenerational effects of low level TCDD exposure are likely inherited. These include significant differential methylation of genes involved in reproduction, endocrine function, xenobiotic metabolism, and epigenetic processing. Notably, a number of histone modification genes were both differentially methylated and expressed in all generations, and many differentially methylated genes overlapped between multiple generations. Collectively, our results suggest that DNA methylation is a promising mechanism to explain male-mediated transgenerational reproductive effects of TCDD exposure in zebrafish, and these effects are likely inherited through integration of multiple epigenetic pathways.

Epigenetic Transgenerational Modifications Induced by Xenobiotic Exposure in Zebrafish

“…In permethrin exposure, changes of DMR in both sexes on chromatin remodeling 24 (chr24) and vimentin (vim) genes were observed, with modifications in the same sites from F0 to F2; furthermore, sex-specific differentially methylated regions (DMR) were found related to the paternal inheritance of F0 to F2 in fragile-X mental retardation protein translational regulator 1 (fmr1) and prepronociceptin b (pnocb) genes, both related to the development of the zebrafish nervous system (Blanc et al, 2021). As with permethrin, Akemann et al (2020) observed that exposure to 2,3,7,8-tetrachlorodibenzo-pdioxin (TCDD) in male zebrafish did not generate changes in global methylation in gonads at any generation; however, they did observe DMRs from F0 to F2. In the F1 generation, 159 genes with differential methylation and expression were identified, while in F2 there were five, pre-B-cell leukemia homeobox 3b (pbx3b; transcriptional activator), si:dkey-266f7.5 (unknown function), snail family zinc finger 3 (snai3; roles in mesodermal formation during embryogenesis; involved in spermatogenesis), transmembrane protein 132E (tmem132e; required for normal inner ear hair cell function and hearing), and calpain 7 (capn7; member of the calpain family of proteins), all except tmem132e showed differential methylation in the three generations.…”

Challenging dogmas: How transgenerational epigenetics reshapes our views on life

“…For example, in nematodes, the plastic component Bisphenol A causes transgenerational reproductive defects that are dependent on two histone modifications, H3K9me3 and H3K27me3 (Camacho et al, 2018; Weinhouse et al, 2018). Endocrine disruptors also lead to detectable transgenerational changes in DNA methylation in Zebrafish (Akemann et al, 2020) as well as in rats (Gillette et al, 2018). In the latter study, the authors examined the number of differentially methylated regions (DMRs) occurring in sperm and specific brain nuclei involved in stress response and social behavior caused by in utero exposure to two endocrine disruptors Vinclozolin and the polychlorinated biphenyl mixture A1221.…”