Superfund Research Program
Mechanisms and Impacts of PCB Resistance in Fish
Project Leader: Mark E. Hahn (Woods Hole Oceanographic Institution)
Co-Investigators: Sibel I. Karchner (Woods Hole Oceanographic Institution), Neelakanteswar Aluru (Woods Hole Oceanographic Institution)
Grant Number: P42ES007381
Funding Period: 1995-2020
Project Summary (2017-2020)
The goal of this Boston University Superfund Research Program (BU SRP) Center project is to understand the molecular mechanisms underlying critical adaptive changes occurring in natural populations of fish after long-term, multi-generational exposure to mixtures of contaminants at Superfund sites. The research applies innovative molecular approaches in an ecological context to understand chemical-induced evolutionary changes in signaling pathways implicated in the response to Superfund chemicals. The studies focus on the Atlantic killifish Fundulus heteroclitus, a unique model system for integrated investigation of ecological and mechanistic questions concerning the impact of chemicals at Superfund sites.
At several locations along the Atlantic coast, including the New Bedford Harbor (NBH), MA Superfund site, populations of killifish have evolved resistance to the highly toxic, dioxin-like (non-ortho-substituted) polychlorinated biphenyls (PCBs) and other chemicals that act through the aryl hydrocarbon receptor (AHR). Recent studies from the BU SRP show that NBH killifish also appear to have reduced sensitivity to non-dioxin-like (ortho-substituted) PCBs-the most abundant components of PCB mixtures-but the mechanisms involved are not known. While allelic variation at killifish AHR loci has been associated with resistance to dioxin-like PCBs, recent studies have implicated another AHR pathway member, AHR-interacting protein (AIP; also known as Ara9 or XAP2) as the strongest candidate for a resistance gene in killifish populations exhibiting reduced sensitivity to dioxin-like compounds.
The central hypothesis of this BU SRP project is that the evolution of resistance to dioxin-like PCBs involves additive or epistatic interactions between multiple components of the AHR pathway, including AIP and one or more of the four killifish AHRs. To test this hypothesis, the researchers are using CRISPR-Cas9 genome-editing technology to generate null and hypomorphic alleles of AIP in killifish and zebrafish and to use these mutant fish to test hypotheses about the role of AIP in the mechanism of resistance to dioxin-like compounds. They are also identifying AIP single nucleotide polymorphisms (SNPs) associated with the resistant phenotype in PCB-resistant killifish, and using CRISPR-Cas9- mediated, single-nucleotide genome editing of zebrafish AIP to study the role of one selected AIP SNP in the mechanism of PCB-resistance. Further studies will target additional SNPs. The AIP-mutant zebrafish generated by this research, and AIP-mutant killifish whose generation is initiated in these studies, will be used in future research to elucidate the role of AIP in the toxicity and evolved resistance to PCBs. This research represents a unique opportunity to establish a novel mechanism of population-level effects of pollutants and advances understanding of the long-term impact of chemical mixtures on ecological systems.