Abstract
AbstractPhylogenetic 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 major phylogenetic groups of mollusc, amphibian, fish and aquatic mammal. 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 nonsynonymous nucleotide substitutions per nonsynonymous site (d~N~) and synonymous nucleotide substitutions per synonymous site (d~S~) 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 by gene duplication events. The d~N~ values indicate that AhR pathway genes are well conserved in aquatic animals, except for CYP1A gene. Furthermore, the d~N~ value indicates that AhR pathway genes are less conserved in fish than in any other aquatic animals, and they likely go through an adaptive evolution within aquatic animals.
Highlights
Persistent organic pollutants (POPs) are organic compounds of natural or anthropogenic origin that resist photolytic, chemical, and biological degradation
Most of them can be classified into three groups:(1) industrial chemical product such as polychlorinated biphenyls (PCBs); (2) combustion and by-products such as Polychlorinated dibenzo-p-dioxins (PCDDs),polychlorinated dibenzofurans (PCDFs),2,3,7,8- tetrachlorodibenzop-dioxin (TCDD); (3) and pesticides such as dichlorodiphenyltrichloroethane (DDT), dihedron, toxaphene
In order to obtain the details of the early evolution of toxicology regulation mechanism of AhR pathway, it was essential to study the evolutionary behavior of the known AhR pathway genes in the major aquatic animals
Summary
Persistent organic pollutants (POPs) are organic compounds of natural or anthropogenic origin that resist photolytic, chemical, and biological degradation They are low water solubility and high lipid solubility, resulting in bioaccumulation in fatty tissues of living organisms (Cumanova et al 2007). The diversity of AhR pathway genes and the species difference of the complicated regulation process of toxicology in different aquatic animals may throw light on the history of early molecular evolution. In order to obtain the details of the early evolution of toxicology regulation mechanism of AhR pathway, it was essential to study the evolutionary behavior of the known AhR pathway genes in the major aquatic animals. The current study investigates the molecular phylogeny of the AhR pathway genes, the gene’s diversity and the patterns of selection, and infers the evolutionary behavior of AhR pathway genes and the protein constitute the pathway in the major aquatic animals. These phylogenies will contribute to the study of structural and sequence diversity and make it possible to characterize and infer the evolutional behavior of AhR pathway genes that constitute the diverse pathway in aquatic animals, and understanding the functional evolution of these genes is essential to predict and interpret species differences in sensitivity to toxicity caused by POPs
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