Cytochrome P450 CYP6L1 is specifically expressed in the reproductive tissues of adult male German cockroaches, Blattella germanica (L.)

Abstract

A full-length cDNA encoding a new cytochrome P450, CYP6L1, was cloned from German cockroaches, Blattella germanica. CYP6L1 has an open reading frame of 1509 nucleotides with a deduced protein of 503 amino acids and molecular mass of 57 Kd. CYP6L1 is most similar to CYP6H1, a putative ecdysone 20-hydroxylase from Locusta migratoria. CYP6L1 mRNA was not detected in embryos nor nymphs, nor in adult females. CYP6L1 mRNA was detected only in the testes and accessory glands of male adult German cockroaches. Given that the testes and accessory glands are the most important components of the reproductive system in male insects, the expression of CYP6L1 mRNA exclusively in these tissues strongly suggests that CYP6L1 has a role in reproduction. Possible substrates for CYP6L1 are discussed.

Introduction

Cytochrome P450s (P450s) are an important enzymatic system found in all organisms examined, including bacteria, fungi, plants and animals. Each animal has approximately 80 (Caenorhabditis elegans, (Consortium, 1998)) to 90 (Drosophila melanogaster, (Adams et al., 2000)) P450s, and some can metabolize numerous substrates (Bernhardt, 1995, Guengerich, 1995, Nebert and Gonzalez, 1987). P450s are named CYP followed by a number, letter and number indicating the family, subfamily and individual isoform (Nelson et al., 1996). In this system, individual P450s with >40% amino acid sequence identity are usually grouped into the same family, and those with >55% identity grouped into the same subfamily. However, there are several exceptions. For example, CYP6A1 and CYP6B2 are <40% identical, but are both grouped into family 6 because “sequences surrounding the conserved cysteine residue make it clear that these two genes are evolutionarily related” (Nelson et al., 1993). Given that this nomenclature system is based on the overall sequence similarity, and that a minor change in a single amino acid can alter substrate specificity (Lindberg and Negishi, 1989), substrate preference cannot be assumed for a certain P450 based on its name.

Insect P450s catalyze the metabolism of plant allelochemicals and insecticides, as well as physiologically important endogenous compounds including juvenile hormones (JHs), ecdysteroids and pheromones (Berenbaum, 1999, Feyereisen, 1999, Hodgson, 1985, Scott et al., 1998). Among the insect P450s, CYP6B1 (Ma et al., 1994) and CYP6B4 (Hung et al., 1997) were shown to metabolize plant allelochemicals (furanocoumarins). CYP6A1 (Andersen et al., 1994), CYP6A2 (Dunkov et al., 1997), CYP6D1 (Wheelock and Scott, 1992, Zhang and Scott, 1996) and CYP12A1 (Guzov et al., 1998) have been shown to metabolize insecticides. CYP4C7 was demonstrated to metabolize JHs and JH precursors (Sutherland et al., 1998). CYP6A1 also metabolizes JHs and their analogs (Andersen et al., 1997). The cloning of these P450s offers a great opportunity to better understand the roles of P450s in herbivore–plant interactions, insecticide resistance, insect development and physiology.

P450s have been implicated in insect reproduction (Hodgson, 1985, Yu and Terriere, 1974). However, no individual insect P450 has yet been associated with reproduction. Herein, we report cloning of the full-length cDNA of the first sex-specific insect P450, CYP6L1, which is exclusively expressed in the reproductive system of male adult German cockroaches. This finding has important implications for understanding the roles of P450s in insect reproduction and may offer a potential target for the development of novel insect control agents.