Genome-wide analysis of chitin synthase and chitinase gene families in African malaria mosquito, Anopheles gambiae

Chitin metabolism represents an attractive target site for combating insect pests as insect growth and development are strictly dependent on precisely toned chitin synthesis and degradation and this pathway is absent in humans and other vertebrates. We identified and characterized two chitin synthase genes (AgCHS1 and AgCHS2), and 20 chitinase and chitinase-like genes (groups I-VIII) presumably responsible for chitin biosynthesis and degradation, respectively, in African malaria mosquito (Anopheles gambiae). Immunohistochemistry analysis and developmental stage- and tissue-dependent transcript profiling by using reverse transcription PCR, quantitative real-time PCR, and in situ hybridization revealed new information on these genes. Chitinase and chitinase-like genes are highly diverse in their gene structure, domain organization, and stage- and tissue-specific expression patterns. Functional analysis of each chitin synthase gene was conducted by using the chitosan/dsRNA nanoparticle-based RNA interference (RNAi) through larval feeding. The repression of AgCHS1 transcript and the reduction of chitin content resulting from the RNAi suggested the systemic nature of RNAi in the larvae. In addition, we demonstrated that silencing of AgCHS1 increased larval susceptibilities to diflubenzuron, whereas silencing of AgCHS2 enhanced the peritrophic matrix disruption and thus increased larval susceptibilities to calcofluor white or dithiothreitol. These results suggest a great potential for using such a nanoparticle-based RNAi technology for high-throughput screening of gene functions and for developing novel strategies for pest management.