A Reduced Transcriptome Approach to Assess Environmental Toxicants Using Zebrafish Embryo Test

Omics approaches can monitor responses
and alterations of biological
pathways at genome-scale, which are useful to predict potential adverse
effects by environmental toxicants. However, high throughput application
of transcriptomics in chemical assessment is limited due to the high
cost and lack of “standardized” toxicogenomic methods.
Here, a reduced zebrafish transcriptome (RZT) approach was developed
to represent the whole transcriptome and to profile bioactivity of
chemical and environmental mixtures in zebrafish embryo. RZT gene
set of 1637 zebrafish Entrez genes was designed to cover a wide range
of biological processes, and to faithfully capture gene-level and
pathway-level changes by toxicants compared with the whole transcriptome.
Concentration–response modeling was used to calculate the effect
concentrations (ECs) of DEGs and corresponding molecular pathways.
To validate the RZT approach, quantitative analysis of gene expression
by RNA-ampliseq technology was used to identify differentially expressed
genes (DEGs) at 32 hpf following exposure to seven serial dilutions
of reference chemical BPA (10–10E–5μM)
or each of four water samples ranging from wastewater to drinking
water (relative enrichment factors 10–6.4 × 10–4). The RZT-ampliseq-embryo approach was both sensitive and able to
identify a wide spectrum of biological activities associated with
BPA exposure. Water quality was benchmarked based on the sensitivity
distribution curve of biological pathways detected using RZT-ampliseq-embryo.
Finally, the most sensitive biological pathways were identified, including
those linked with adverse reproductive outcomes, genotoxicity and
development outcomes. RZT-ampliseq-embryo approach provides an efficient
and cost-effective tool to prioritize toxicants based on responsiveness
of biological pathways.