Genome-wide search and characterization of chitinase gene family in African malaria mosquito (Anopheles gambiae)

Chitinases are digestive enzymes that break down glycosidic bonds in chitin, an important exoskeletal element of insects and other arthropods. Through a manual genome-wide search, we identified 17 putative chitinase genes from the African malaria mosquito (Anopheles gambiae) and assigned these genes into five different chitinase classes (I-V). The total number of chitinase genes in A. gambiae is similar to those identified in other insect species. Both chitinase-like genes (AgChtIDGF4 and AgChtIDGFz) appeared to be constitutively expressed in all developmental stages as determined by RT-PCR, whereas other genes were only expressed in certain developmental stages. Specifically, AgCht2z, AgCht3z, AgCht4, AgCht5, AgCht9, AgCht12 and AgCht13 appeared to be expressed only in the late egg stage and larval stages, whereas AgCht8 was only expressed in the pupal and adult stages. Our tissue-specific gene expression analysis revealed that AgChtIDGFz, AgCht1z and AgCht4z were constitutively expressed in all four tissues examined, including foregut, midgut, hindgut and carcass. In contrast, AgCht2 and AgCht12 were mainly expressed in the foregut, AgCht13 in the midgut, and AgCht5 in the whole gut, whereas AgCht6 was only expressed in the carcass. Other chitinase genes were expressed in both the certain regions of the gut and the carcass with variable expression levels. Functional analysis of the selected genes is currently being pursued by using RNAi. This study is expected to provide new insight into the functions of these genes in chitin metabolism in insects.