Molecular cloning of cytochrome P4501A cDNA of medaka (Oryzias latipes) and messenger ribonucleic acid regulation by environmental pollutants

The sequence of cytochrome P4501A (CYP1A) cDNA of medaka (Oryzias latipes) was determined, and its messenger ribonucleic acid (mRNA) regulation by β‐naphthoflavone (βNF) was evaluated. The determined cDNA sequence contained 2,349 base pairs (bp), and the open reading frame contained a total of 1,563 bp encoding 521 predicted amino acids. The induction of CYP1A mRNA in medaka was evaluated using reverse transcription—polymerase chain reaction. The concentration—dependent induction of CYP1A mRNA in the liver was observed after exposure to βNF at nominal concentrations of 20, 100, and 500 μg/ L for 2 d. Time‐dependent changes of CYP1A mRNA levels were also observed in the liver, gill, gut, and caudal fin tissues of medaka exposed to 100 μg/L of βNF for 7 d. Our results showed that the degree of CYP1A mRNA induction in the gill, gut, and caudal fin after exposure to βNF was relatively higher than that in the liver, possibly because of low basal levels of CYP1A mRNA in the gill, gut, and caudal fin of nonexposed fish. The induction of medaka CYP1A mRNA was also observed after exposure to an environmental sample, landfill leachate. The CYP1A mRNA inductions in the gill, gut, and caudal fin were also higher than that in the liver as shown in the βNF‐treated groups. These results show that CYP1A mRNA determination in the gill, gut, and caudal fin, which are in direct contact with the polluted water, may become a useful method for monitoring CYP1A‐inducible chemicals.