BACKGROUND

A structurally diverse group of chemicals, including dioxins [e.g., 2,3,7,8-tetrachlorodibenzo--dioxin (TCDD)] and polycyclic aromatic hydrocarbons (PAHs), can xenobiotically activate the aryl hydrocarbon receptor (AHR) and contribute to adverse health effects in humans and wildlife. In the zebrafish model, repression of has a causal role in several AHR-mediated toxic responses, including craniofacial cartilage malformations; however, the mechanism of repression remains unknown. We previously identified a long noncoding RNA, long intergenic noncoding RNA (), which is increased (in an AHR-dependent manner) by multiple AHR ligands and is required for the AHR-activated repression of .

OBJECTIVE

Using the zebrafish model, we aimed to enhance our understanding of the signaling events downstream of AHR activation that contribute to toxic responses by identifying: ) whether is enriched on the locus, ) 's functional contributions to TCDD-induced toxicity, ) PAHs that increase expression, and ) mammalian orthologs of .

METHODS

We used capture hybridization analysis of RNA targets (CHART), qRT-PCR, RNA sequencing, morphometric analysis of cartilage structures, and hemorrhaging screens.

RESULTS

The transcript was enriched at the 5' untranslated region (UTR) of the locus. Transcriptome profiling and human ortholog analyses identified processes related to skeletal and cartilage development unique to TCDD-exposed controls, and angiogenesis and vasculature development unique to TCDD-exposed zebrafish that were injected with a splice-blocking morpholino targeting . In comparison to TCDD exposed control morphants, morphants exposed to TCDD resulted in abnormal cartilage structures and a smaller percentage of animals displaying the hemorrhaging phenotype. In addition, expression was significantly increased in six out of the sixteen PAHs we screened.

CONCLUSION

Our study establishes that in zebrafish, is recruited to the 5' UTR to repress transcription, can regulate cartilage development, has a causal role in the TCDD-induced hemorrhaging phenotype, and is up-regulated by multiple environmentally relevant PAHs. These findings have important implications for understanding the ligand-specific mechanisms of AHR-mediated toxicity. https://doi.org/10.1289/EHP3281.