In silico characterization and comparative genomic analysis of the Culex quinquefasciatus glutathione S-transferase (GST) supergene family

Abstract

The glutathione S-transferases (GSTs) are phase II class of detoxification enzymes that are involved both directly and indirectly in insecticide resistance mechanisms. The Culex quinquefasciatus GST superfamily was analyzed by utilizing the public domain Culex genome sequence. In total, 35 cytosolic (seven classes) and 5 microsomal putatively active GSTs were retrieved, classified, and annotated. The study revealed the presence of three unclassified GSTs. Of 35 cytosolic GSTs, 65% contributed by insect specific Delta-Epsilon classes. Gene cluster analysis revealed that most of the genes of Delta, Epsilon, and Theta classes were organized into gene clusters. The gene organization analysis revealed the dominance of phase "0" introns in the Culex GST family. The studies on intron loss and gain events revealed that the Delta GSTs have experienced a higher number of loss and gains during their evolution. A positive correlation was observed between the phylogenetic relationship of members of the GST superfamily and their corresponding exon-intron organization. In addition, the genes within the gene clusters revealed the monophyletic phylogenetic relationship implying the importance of gene duplication events in the gene families' evolution. Finally, the comparative genomic analysis has shown a complex evolutionary scenario associated with the GST supergene family evolution in insects.

Genomic Insights into the Glutathione S-Transferase Gene Family of Two Rice Planthoppers, Nilaparvata lugens (Stål) and Sogatella furcifera (Horváth) (Hemiptera: Delphacidae)

“… D. m , Drosophila melanogaster [64]; A. g , Anopheles gambiae [65]; A. a , Aedes aegypti [66]; C. q , Culex quinquefasciatus [41]; A. m , Apis mellifera [67]; N. v , Nasonia vitripennis [68]; T. c , Tribolium castaneum [69]; B. m, Bombyx mori [70]; A. p , Acyrthosiphon pisum [71]; N. l , Nilaparvata lugens . Values in parentheses are species totals of all GST subclasses.…”

Identification and classification of detoxification enzymes from Culex quinquefasciatus (Diptera: Culicidae)

“…Of these, Delta-and Epsilon-classes are important for the detoxification of xenobiotics [11, 23]. The GST supergene family forms the phase II detoxification system where the conjugation reactions occur to render the xenobiotics more soluble or to make them sequestered so that xenobiotics or insecticides will become inactive in the cell.…”

“…The comparative GST supergene family analysis suggests that 55 to 66% of total GSTs belong to the Delta-Epsilon class. Delta-Epsilon classes are primarily responsible for detoxification process while the function of other GST classes is yet to be elucidated [23]. The comparative genomic analysis show that classes Iota, Unclassified, and Microsomal GSTs are absent from the Drosophila , while class Zeta is absent from the Culex .…”

Culex genome is not just another genome for comparative genomics

“…aegypti it is known that a small portion of the detoxification enzymes' repertoire is responsible for the insecticide resistance phenotype [20]. A preliminary analysis on Culex detoxification systems revealed the presence of a total of 268 detoxification genes [21](Reddy and Raghavendra, unpublished results). However, given the fact that mosquitoes might get exposed to numerous varieties of xenobiotics during their complex life cycle, how these detoxifying enzymes can help to protect the mosquito against insecticides needs to be addressed.…”