Identification of the Full 46 Cytochrome P450 (<i>CYP</i>) Complement and Modulation of <i>CYP</i> Expression in Response to Water-Accommodated Fractions of Crude Oil in the Cyclopoid Copepod <i>Paracyclopina nana</i>

The 46 cytochrome P450 (<i>CYP</i>) gene superfamily was identified in the marine copepod <i>Paracyclopina nana</i> after searching an RNA-seq database and comparing it with other copepod <i>CYP</i> gene families. To annotate the 46 <i>Pn-CYP</i> genes, a phylogenetic analysis of <i>CYP</i> genes was performed using a Bayesian method. <i>Pn-CYP</i> genes were separated into five different clans: CYP2, CYP3, CYP20, CYP26, and mitochondrial. Among these, the principal <i>Pn-CYP</i> genes involved in detoxification were identified by comparing them with those of the copepod <i>Tigriopus japonicus</i> and were examined with respect to their responses to exposure to a water-accommodated fraction (WAF) of crude oil and to the alkylated forms of two polycyclic aromatic hydrocarbons (PAHs; phenanthrene and fluorene). The expression of two <i>Pn-CYP3027</i> genes (<i>CYP3027F1</i> and <i>CYP3027F2</i>) was increased in response to WAF exposure and also was upregulated in response to the two alkylated PAHs. In particular, <i>Pn-CYP3027F2</i> showed the most notable increase in response to 80% WAF exposure. These two responsive <i>CYP</i> genes (<i>Pn-CYP3027F1</i> and <i>CYP3027F2</i>) were also phylogenetically clustered into the same clade of the WAF- and alkylated PAH-specific <i>CYP</i> genes of the copepod <i>T. japonicus</i>, suggesting that these <i>CYP</i> genes would be those chiefly involved in detoxification in response to WAF exposure in copepods. In this paper, we provide information on the copepod <i>P. nana CYP</i> gene superfamily and also speculate on its potential role in the detoxification of PAHs in marine copepods. Despite the nonlethality of WAF, <i>Pn-CYP3027F2</i> was rapidly and significantly upregulated in response to WAF that may serve as a useful biomarker of 40% or higher concentration of WAF exposure. This paper will be helpful to better understand the molecular mechanistic events underlying the metabolism of environmental toxicants in copepods