A fatty acid synthase gene (FASN3) from the integument tissue of Rhodnius prolixus contributes to cuticle water loss regulation.

Fatty acid synthase is a multifunctional enzyme involved in the formation of fatty acids. Despite the role of fatty acids in cell signalling and energy metabolism, and as precursors to pheromones and hydrocarbons that waterproof the cuticle, the insect fatty acid synthases have been scarcely studied. Here we perform the molecular characterization of three fatty acid synthase genes (fatty acid synthase RPRC000123, RPRC000269 and RPRC002909) in the Chagas disease vector, Rhodnius prolixus. Gene expression screening by reverse transcription quantitative PCR showed that RPRC000123 and RPRC002909 are expressed almost exclusively in the integument tissue whilst RPRC000269 is mostly expressed in the fat body and also in several body organs. Phylogenetic analysis, together with gene expression results, showed that RPRC000269, RPRC002909 and RPRC000123 are orthologues of Drosophila melanogaster fatty acid synthase 1 (FASN1), FASN2 and FASN3 genes, respectively. After RNA interference-mediated knockdown of RPRC000123, insects died immediately after moulting to the next developmental stage. However, mortality was prevented by placing the insects under saturated humidity conditions, suggesting that dehydration might play a role in the insects' death. Lipid analyses in RPRC000123-silenced insects showed reduced amounts of integument fatty acids and methyl-branched hydrocarbons, compared to controls. These data support an important role for FASN3 in the biosynthesis of the precursors to hydrocarbons that waterproof the insect cuticle.