GSE203631
Multigenerational Effects of Dietary Benzo[a]pyrene Exposure on Behavior, Gene Expression, and DNA Methylation
Benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon (PAH), is implicated in many developmental and behavioral adverse outcomes in offspring of exposed parents.  Following a dietary preconceptional exposure to BaP in zebrafish, the objective of this study was to compare parental sex-dependent adverse outcomes in F1 and F2 offspring with the transcriptomic and epigenetic changes in eggs, sperm, and 10-hour post fertilization (hpf) embryos. Adult wild-type (5D) zebrafish were fed 708 µg BaP/g diet (measured) at a rate of 1% body weight twice/day (14 µg BaP/g fish/day) for 21 days. Fish were spawned using a crossover design and parental (F0) behavior and reproductive indexes measured. In offspring behavioral effects were measured at 96 hours post fertilization (hpf) in F1 & F2 larvae, and again when F1s were adult. Compared to controls, there was no significant effect of BaP exposure on adult behavior in F0, but locomotor behavior was significantly increased in F1 adults of both sexes. Larval behavior (96 hpf, photomotor response assay) was significantly altered in both the F1 and F2 generations following parental BaP exposure. To assess parental sex-dependent molecular mechanisms, BaP-mediated differential gene expression and DNA methylation changes were measured using RNAseq and RRBS, respectively, on F0 sperm and eggs and the 10 hpf embryos from all four crosses in F1 generation. Embryos resulting from the BaP male and control female cross had the most differentially methylated regions (DMRs) and differentially expressed genes. Some DMRs were associated with genes encoding chromatin modifying enzymes suggesting regulation of chromatin conformation by DNA methylation. Parental dietary BaP exposure caused persistent behavioral changes wherein the male germline contributed most significantly to the multigenerational adverse outcomes. Overall design: Sexually mature (120 dpf) 5D strain of zebrafish were fed either acetone alone or BaP-treated (25 µg/g fish equivalent to 1250 µg/g food, respectively) TetraMin® Tropical Flakes.  Paired (2x2) zebrafish in five replicate tanks per treatment group (N=5 replicate tanks for a total 20 fish/group) were allowed to acclimate for a week while maintained at 25.5-28°C and fed twice daily with untreated flakes and Gemma 300 micron food. During the exposure, fish were fed 1% body weight twice daily of the corresponding dose of BaP-treated flake food and once daily Gemma 300 micro food for 21 days. At the end of day 21, a cross-over breeding design was implemented to assess sex-specific contributions into the following groups: control males x control females, BaP females x control males, BaP males x control females, and BaP males x BaP females. On days 22 and 23 (no longer being exposed), eggs were collected to determine reproductive success. On day 24 (females) and day 25 (males), fish were euthanized, and gonad, liver, and brain were collected biobanked for future analysis. Furthermore, sperm or eggs from the BaP exposed and control fish, along with 10 hpf embryos from each cross (4 crosses) were collected for RNA-seq and DNA methylation analysis.