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Identification and Phylogenetic Characterization of Cytochrome p450 IA (CYP1A) in Little Skate, Raja erinacea

Danielle Gilbert
Department of Biology,Massachusetts Institute of Technology, Cambridge, MA 02139
Work conducted with Dr. Rebeka Merson in the laboratory of Dr.Mark Hahn,Woods Hole Oceanographic Institution,Woods Hole, MA 02543

 
   
Non-Scientific Abstract

Phylogenetics is the study of evolutionary relationships.Historically, this field utilized morphological studies,which analyze the physical characteristics of organisms to classify relationships.Recent advances in molecular biology allow researchers to organize evolutionary relationships through the examination of DNA. By characterizing one gene in number of species, researchers can construct the same ³trees of life² as those from morphological studies. Sometimes molecular techniques reveal surprising results, changing the trees to show a more correct relationship. In this study, we examine a gene in the little skate, Raja erinacea.We chose the little skate as our model organism for several reasons: (1) it is representative of the earliest jawed vertebrates, cartilaginous fish; (2) among cartilaginous fish, skates and rays are one of the oldest groups, second only to chimeras; and (3) the little skate is small, easily handled, and was readily available for study. The gene we selected is cytochrome p450 1A (CYP1A).The CYP1A protein metabolizes common pollutants, including TCDD.This metabolic process may release carcinogens.We hope to find and sequence the CYP1A gene in the little skate, and then compare its sequence to those of CYP1A genes in other animals to place the little skate CYP1A in a phylogenetic tree.

Abstract

Cytochrome p450 IA (CYPIA) is a xenobiotic metabolizing enzyme involved in the hydrolysis of numerous environmental toxins, including halogenated and polynuclear aromatic hydrocarbons. This biotransformation releases free radicals and other mutagenic metabolites, resulting in most of the deleterious effects observed with these pollutants.CYP1A is induced by toxic compounds through a ligand-activated transcription factor, the aryl hydrocarbon receptor (AHR). A significant inducer of AHR is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a common contaminant that results from chemical bleaching and the manufacture of organochlorine compounds. The AHR/CYP1A regulatory system is well-known in many vertebrate taxa from mammals to bony fish, though the natural physiologic function has yet to be determined. Studies of the evolutionary history of AHR and CYP1A may reveal this function and its significance.Here we report cDNA cloning of CYP1A in an elasmobranch, the little skate Raja erinacea. The presence of a CYP1A ortholog in this ancient lineage suggests that CYP1A arose before the divergence of bony and cartilaginous fish.