Circadian regulation of permethrin susceptibility by glutathione S-transferase (BgGSTD1) in the German cockroach (Blattella germanica) Yu-Hsien Lin a,1 , Chi-Mei Lee b,1 , Jia-Hsin Huang a , How-Jing Lee a,⇑ a Department of Entomology, National Taiwan University, Taipei, Taiwan b Department of Life Science, National Taiwan Normal University, Taipei, Taiwan article info Article history: Received 8 January 2014 Received in revised form 22 April 2014 Accepted 1 May 2014 Available online 10 May 2014 Keywords: Permethrin RNAi Circadian rhythm GSTD1 abstract The daily susceptibility rhythm to permethrin and the expression level of the delta class glutathione S-transferase (BgGSTD1) gene were investigated in Blattella germanica. Male cockroaches were exposed to the same concentration of permethrin at different times in a light-dark cycle, and results showed that the highest resistance occurred at night. Furthermore, the circadian rhythmicity of permethrin suscepti- bility was demonstrated by the highest resistance at subjective night under constant darkness. The mRNA level of the BgGSTD1 gene in the fat body of B. germanica peaked early in the day or subjective day under light-dark or constant dark conditions, whereas enzyme activity of cytosolic GSTs did not reflect the rhythmic pattern as well as BgGSTD1 expression. RNA interference (RNAi) was employed to study the function of BgGSTD1 in the circadian rhythm of permethrin susceptibility in B. germanica. Both BgGSTD1 mRNA level and cytosolic GSTs activity were significantly decreased by dsGSTD1 injection. In addition, survival of B. germanica with silenced BgGSTD1 was significantly decreased at night but not in the day when the cockroaches were exposed to permethrin. Total cytosolic GSTs activity demonstrated that is not the only gene involved in the circadian regulation of the permethrin resistance, although it is one of the major regulators of permethrin resistance. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Circadian rhythms of physiological functions and behavioral patterns are generally displayed in living organisms to adapt and synchronize the organism with periodic changes in the environment (Ishida et al., 1999). The molecular mechanisms of circadian regula- tion in the detoxification system have been well studied in mamma- lians due to the consequence of drug administration (Gachon and Firsov, 2011). The xenobiotic metabolism (XM) genes in mammals are highly conserved in insects such as glutathione S-transferase (GST), esterase, cytochrome P450 (CYP450) and UDP-glucuronosyl- transferase (UGT)(Casida and Quistad, 2004). In addition, insects share numerously orthologous components in the negative feed- back loops of circadian clock system with mammals (Beaver et al., 2010; Doherty and Kay, 2010; Zmrzljak and Rozman, 2012). There- fore, insects can serve as a good model to study the circadian regu- lation of the toxicant metabolism and evolutionary comparison of chronotoxicity mechanisms between different taxa. The daily rhythm of insecticide susceptibility has described in insects (Eesa and Cutkomp, 1995). Many taxa of insects exhibit a daily variation of tolerance when they are exposed to a standard dose of insecticides or chemicals at different times during the day (Beck, 1963; Fondacar and Butz, 1970; Nowosielski et al., 1964; Onyeocha and Fuzeau-Braesch, 1991). Experiments based on micro- array analysis and mRNA sequencing have provided new insights on transcriptomes of clock-controlled genes (Ceriani et al., 2002; Panda et al., 2002; Rodriguez-Zas et al., 2012; van der Linden et al., 2010). The circadian oscillation of several XM genes has been described in Drosophila melanogaster, Aedes aegypti, and Anopheles gambiae respectively (McDonald and Rosbash, 2001; Ptitsyn et al., 2011; Rund et al., 2011). There are XM genes involved in the phase I group such as the CYP450 superfamily, esterase, as well as in the phase II group such as UGT, GST, with highest expression levels at specific times of the day. In addition, functional genomic studies using dis- rupted clock oscillation have demonstrated that rhythmic expres- sion of CYP450 and UGT are involving in the circadian variation of susceptibility to insecticides in D. melanogaster and Ae. aegypti (Hooven et al., 2009; Yang et al., 2010). Based on these studies, insec- ticide susceptibility is suggested to be under circadian clock control. Until now, however, few studies have demonstrated circadian regulation of insecticide susceptibility to GSTs, which are the http://dx.doi.org/10.1016/j.jinsphys.2014.05.001 0022-1910/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Address: Department of Entomology, National Taiwan University, #1, Sec. 4, Roosevelt Rd., Taipei 106, Taiwan. Tel.: +886 223636581. E-mail address: m480@ntu.edu.tw (H.-J. Lee). 1 These authors contributed equally to this work. Journal of Insect Physiology 65 (2014) 45–50 Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys