Pollen diet mediates how pesticide exposure impacts brain gene expression in nest-founding bumble bee queens.

A primary goal in biology is to understand the effects of multiple, interacting environmental stressors on organisms. Wild and domesticated bees are exposed to a wide variety of interacting biotic and abiotic stressors, with widespread declines in floral resources and agrochemical exposure being two of the most important. In this study, we used examinations of brain gene expression to explore the sublethal consequences of neonicotinoid pesticide exposure and pollen diet composition in nest-founding bumble bee queens. We demonstrate for the first time that pollen diet composition can influence the strength of bumble bee queen responses to pesticide exposure at the molecular level. Specifically, one pollen mixture in our study appeared to buffer bumble bee queens entirely against the effects of pesticide exposure, with respect to brain gene expression. Additionally, we detected unique effects of pollen diet and sustained (versus more temporary) pesticide exposure on queen gene expression. Our findings support the hypothesis that nutritional status can help buffer animals against the harmful effects of other stressors, including pesticides, and highlight the importance of using molecular approaches to explore sublethal consequences of stressors.

Maternal-to-zygotic transition as a potential target for niclosamide during early embryogenesis.

Niclosamide is an antihelminthic drug used worldwide for the treatment of tapeworm infections. Recent drug repurposing screens have highlighted the broad bioactivity of niclosamide across diverse mechanisms of action. As a result, niclosamide is being evaluated for a range of alternative drug-repurposing applications, including the treatment of cancer, bacterial infections, and Zika virus. As new applications of niclosamide will require non-oral delivery routes that may lead to exposure in utero, it is important to understand the mechanism of niclosamide toxicity during early stages of embryonic development. Previously, we showed that niclosamide induces a concentration-dependent delay in epiboly progression in the absence of effects on oxidative phosphorylation - a well-established target for niclosamide. Therefore, the overall objective of this study was to further examine the mechanism of niclosamide-induced epiboly delay during zebrafish embryogenesis. Based on this study, we found that (1) niclosamide exposure during early zebrafish embryogenesis resulted in a decrease in yolk sac integrity with a concomitant decrease in the presence of yolk sac actin networks and increase in cell size; (2) within whole embryos, niclosamide exposure did not alter non-polar metabolites and lipids, but significantly altered amino acids specific to aminoacyl-tRNA biosynthesis; (3) niclosamide significantly altered transcripts related to translation, transcription, and mRNA processing pathways; and (4) niclosamide did not significantly alter levels of rRNA and tRNA. Overall, our findings suggest that niclosamide may be causing a systemic delay in embryonic development by disrupting the translation of maternally-supplied mRNAs, an effect that may be mediated through disruption of aminoacyl-tRNA biosynthesis.

mRNA-Sequencing Identifies Liver as a Potential Target Organ for Triphenyl Phosphate in Embryonic Zebrafish.

Triphenyl phosphate (TPHP) is a commonly used organophosphate flame retardant and plasticizer in the United States. Using zebrafish as a model, the overall objective of this study was to identify potential organs that might be targeted by TPHP during embryonic development. Based on mRNA-sequencing, TPHP exposure from 24 to 30 h post fertilization (hpf) and 24 to 48 hpf significantly affected the abundance of 305 and 274 transcripts, respectively, relative to vehicle (0.1% DMSO) controls. In addition to minor effects on cardiotoxicity- and nephrotoxicity-related pathways, ingenuity pathway analysis (IPA) of significantly affected transcripts within 30- and 48-hpf embryos revealed that hepatotoxicity-related pathways were strongly affected following exposure to TPHP-alone. Moreover, although pretreatment with fenretinide (a retinoic acid receptor agonist) mitigated TPHP-induced pericardial edema and liver enlargement at 72 and 128 hpf, respectively, IPA revealed that fenretinide was unable to block TPHP-induced effects on cardiotoxicity-, nephrotoxicity-, and hepatotoxicity-related pathways at 48 hpf, suggesting that TPHP-induced effects on the transcriptome were not associated with toxicity later in development. In addition, based on Oil Red O staining, we found that exposure to TPHP nearly abolished neutral lipids from the embryonic head and trunk and, based on metabolomics, significantly decreased the total abundance of metabolites-including betaine, a known osmoprotectant-at 48 and 72 hpf. Overall, our data suggest that, in addition to the heart, TPHP exposure during early development results in adverse effects on the liver, lipid utilization, and osmoregulation within embryonic zebrafish.

Complex Interplay Among Nuclear Receptor Ligands, Cytosine Methylation, and the Metabolome in Driving Tris(1,3-dichloro-2-propyl)phosphate-Induced Epiboly Defects in Zebrafish.

Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) is a high-production-volume organophosphate flame retardant (OPFR) that induces epiboly defects during zebrafish embryogenesis, leading to the disruption of dorsoventral patterning. Therefore, the objectives of this study were to (1) identify the potential mechanisms involved in TDCIPP-induced epiboly defects and (2) determine whether coexposure to triphenyl phosphate (TPHP)-an OPFR commonly detected with TDCIPP-enhances or mitigates epiboly defects. Although TDCIPP-induced epiboly defects were not associated with adverse impacts on cytoskeletal protein abundance in situ, the coexposure of embryos to TPHP partially blocked TDCIPP-induced epiboly defects. As nuclear receptors are targets for both TPHP and TDCIPP, we exposed the embryos to TDCIPP in the presence or absence of 69 nuclear receptor ligands and, similar to TPHP, found that ciglitazone (a peroxisome proliferator-activated receptor γ agonist) and 17ß-estradiol (E2; an estrogen receptor α agonist) nearly abolished TDCIPP-induced epiboly defects. Moreover, E2 and ciglitazone mitigated TDCIPP-induced effects on CpG hypomethylation within the target loci prior to epiboly, and ciglitazone altered TDCIPP-induced effects on the abundance of two polar metabolites (acetylcarnitine and cytidine-5-diphosphocholine) during epiboly. Overall, our results point to a complex interplay among nuclear receptor ligands, cytosine methylation, and the metabolome in both the induction and mitigation of epiboly defects induced by TDCIPP.