ABSTRACT: Humans are exposed to chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) that cause toxicity through activation of the aryl hydrocarbon receptor (AHR). There is inter-individual variation in sensitivity to effects of AHR ligands, but it is not fully explained by variation in the human AHR, suggesting that other components of the AHR pathway are involved in controlling sensitivity. A clue to the genetic mechanisms underlying differential sensitivity to AHR agonists has emerged recently from studies of Atlantic killifish (Fundulus heteroclitus) populations with multi-generational exposure to PCBs, TCDD, and PAHs. Genomic studies of these populations identified the AHR chaperone AHR-interacting protein (AIP/Ara9/XAP2) as the strongest candidate resistance gene. However, the precise role of AIP in the mechanism of resistance is unknown. To understand the role of AIP in the toxicity of dioxin-like compounds and how variation in AIP may affect chemical sensitivity, we CRISPR-Cas9 to generate AIP loss-of-function alleles in killifish and zebrafish (Danio rerio). Homozygous mutant killifish and zebrafish die during larval development, while heterozygous mutants develop normally, survive to adulthood, and reproduce normally. Prior to death, homozygous mutant zebrafish exhibit reduced sensitivity to embryotoxic effects of exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB126) and TCDD. Gene expression profiling of control and PCB126-exposed larvae at 3 days post-fertilization reveals some genes differentially expressed between mutant and wild-type larvae, but the induction of AHR-regulated genes is similar in aip-/-, aip-/+, and aip+/+ larvae. Understanding the role of AIP in controlling sensitivity to AHR agonists in fish models may shed light on the factors that determine differential susceptibility of humans to dioxin-like compounds and on the role of AIP in human disease.
