Overexpression of the cytochrome c oxidase subunit I gene associated with a pyrethroid resistant strain of German cockroaches, Blattella germanica (L.).

A cytochrome c oxidase subunit I gene (COXI) was identified and isolated as a differentially expressed gene between insecticide susceptible ACY and resistant Apyr-R German cockroach strains using PCR-selected subtractive hybridization and cDNA array techniques. The cDNA sequence of COXI has an open reading frame of 1533 nucleotides encoding a putative protein of 511 amino acid residues. Northern blot analysis indicated that levels of COXI expression were similar in three life stages (eggs, nymphs, and adults) of the susceptible ACY strain. The expression of COXI in the resistant Apyr-R strain was developmentally regulated, with low expression in eggs, an increase (approximately 1.4-fold) in nymphs, and rose to a maximum (approximately 3-fold) in both adult females and males. Comparison of COXI expression between ACY and Apyr-R strains indicated that there was no difference in the eggs of the two strains, but expression was higher (approximately 1.5-fold) in nymphs and much higher (approximately 3- to 4-fold) in adult males and females of the Apyr-R strain. The levels of COXI mRNA showed about 1.4- and 1.7-fold increase in the abdomen tissues compared with the head+thorax tissues of ACY and Apyr-R strains, respectively. Although expression patterns of COXI in head+thorax and abdomen tissues were similar (i.e. lower in the head+thorax tissues and higher in the abdomen tissues) in both the ACY and Apyr-R strains, the expression of COXI was about 2.5-fold higher in the head+thorax and approximately 3-fold higher in the abdomen tissues of the Apyr-R strain compared with the corresponding ACY samples. The overexpression of COXI in resistant German cockroaches merits the investigation of the importance of the gene in insecticide resistant German cockroaches.