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Differential DNA methylation following developmental exposure to triclosan (TCS) in 7dpf zebrafish larvae

ABSTRACT: There is increasing evidences that toxicant exposure can alter methylation profiles, particularly during embryogenesis when DNA methylation patterns are established. In order to investigate the effects of TCS on DNA methylation and its consequences on gene expression during embryogenesis, we exposed zebrafish eggs during 7 days post fertilisation (dpf) to 50 and 100 µg/L of TCS. Although, global DNA methylation was not affected by TCS exposure, a total of 171 differentially methylated fragments (DMFs) between conditions were identified. The majority of the DMFs were found between the two exposed groups, reflecting distinct triggered responses. Gene ontology analysis revealed that pathways involved in TGF-beta signaling were enriched in larvae exposed to 50 µg/L, while de novo pyrimidine biosynthesis functions were overrepresented in fish exposed to 100 µg/L of TCS. In parallel, gene expression analysis revealed a positive correlation between DNA methylation patterns and gene expression levels for introns, together with significant alterations of the transcription of genes involved in nervous system development, transcriptional factors and histone methyltransferase. Overall our work provides evidence that TCS impacts DNA methylation during zebrafish early embryogenesis and brings clues about the toxicity mechanisms of TCS during this critical period of development.

ORGANISM(S): Danio rerio

PROVIDER: GSE105766 | GEO | 2019/10/22

REPOSITORIES: GEO

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Project description:Aiming at the development of a micropollutant biosensor in the frame of the Micro-Ecological Life Support System Alternative (MELiSSA), a pilot study was initiated to identify triclosan (TCS)-responsive biomarker genes in the MELiSSA carbon-mineralizing microorganism, Rhodospirillum rubrum S1H. TCS is a biocide, commonly found in human excrements and is considered an emerging pollutant in wastewater and the environment. Chronic exposure to MELiSSA-relevant concentrations (≥25 µg L-1) TCS caused a significant extension of the lag phase without affecting the growth rate. Analytical determination gave no indication of TCS biodegradation during the growth experiment and flow cytometric viability analyses revealed that TCS is only slightly toxic to R. rubrum. Through microarray analyses, the genetic mechanisms supporting the reversibility of TCS-induced inhibition were scrutinized. Hence, an extremely TCS-responsive cluster of four small adjacent genes was revealed, with up to 34-fold induction at 25 µg L-1. These four genes, for which the name micropollutant-upregulated factor (muf) was proposed; appear to be unique to R. rubrum and are shown for the first time to be involved in the response to stress. Moreover, numerous other systems that are associated with the proton-motive force were shown to be responsive to TCS, but never as highly upregulated as the muf genes. Hence, R. rubrum induced the phage shock protein operon (pspABC), numerous major facilitator efflux systems, cell envelope consolidation mechanisms, oxidative stress response, beta-oxidation, and carbonic anhydrase; while downregulating bacterial conjugation- and carboxysome synthesis genes. The muf genes and three efflux-related genes showed most potential as low-dose biomarkers. The two microarray experiments (10 and 25 µg l-1 Triclosan) were all performed in biological triplicate and containing three (in-slide) technical repeats. For all conditions, the Triclosan exposed sample (Cy5) was compared with the non-exposed solvent control (Cy3) to identify those genes that were differentially expressed upon Triclosan exposure.

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Differential DNA methylation following developmental exposure to triclosan (TCS) in 7dpf zebrafish larvae

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