Molecular phylogenies and evolutionary behavior of AhR (aryl hydrocarbon receptor) pathway genes in aquatic animals: Implications for the toxicology mechanism of some persistent organic pollutants (POPs)

Phylogenetic analysis of AhR pathway genes and their evolutionary rate variations were studied on aquatic animals. The gene sequences for the proteins involved in this pathway were obtained from four major phylogenetic groups, including bivalvia, amphibian, teleostei and mammalia. These genes were distributed under four major steps of toxicology regulation: formation of cytosolic complex, translocation of AhR, heterodimerization of AhR and induction of CYP1A. The NJ, MP, and ML algorithm were used on protein coding DNA sequences to deduce the evolutionary relationship for the respective AhR pathway gene among different aquatic animals. The rate of non-synonymous nucleotide substitutions per non-synonymous site (dN) and synonymous nucleotide substitutions per synonymous site (dS) were calculated for different clade of the respective phylogenetic tree for each AhR pathway gene. The phylogenetic analysis suggests that evolutionary pattern of AhR pathway genes in aquatic animals is characterized mainly through gene duplication events or alterative splicing. The dN values indicate that all AhR pathway genes are well conserved in aquatic animals, except for CYP1A gene. Furthermore, compare with other aquatic animals, the dN value indicates that AhR pathway genes of fish are less conserved, and these genes likely go through an adaptive evolution within aquatic animals.