Expression of AMP genes in Drosophila melanogaster induced by bacterial components – lipopolysaccharide, lipoteichoic acid and peptidoglycan

Innate immunity plays a very important role in combating microbial infection in animals, and it is conserved from flies to mammals. Upon infection, insects mount a rapid antimicrobial response that consists of many components, including antimicrobial peptides. Drosophila melanogaster is devoid of adaptive immune system and relies solely on innate immune reactions for its defense by inducing antimicrobial peptide (AMP) genes as one type of the response. AMP gene drosomycin is induced by Gram-positive peptidoglycan (PG) and fungi and regulated by the Toll pathway, whereas diptericin is induced by Gram-negative PG and regulated by the immune deficiency (Imd) pathway.  In the absence of these two pathways, AMP genes cannot be induced and the flies become more susceptible to many microbes, even those that are normally non-pathogenic.

To gain insight about activation of AMP genes by Gram-positive and Gram-negative bacterial cell wall components, we fed and injected ultra-pure bacterial components in both larvae and adult flies. Total RNAs were extracted from all stages, and activation of drosomycin and diptericin was determined by Real-time PCR.

Our results showed that drosomycin and diptericin could be induced by the six bacterial components tested in D. melanogaster canton-S L3 larvae and adult flies by feeding to some extents. These findings suggest that activation of AMP genes in Drosophila is related to bacterial components, infection time, developmental stage and sex