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

Abstract

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.

Deciphering the role of Rhodnius prolixusCYP4G genes in straight and methyl‐branched hydrocarbon formation and in desiccation tolerance

“…Previous work from our lab silencing the integument FASN3 in R. prolixus showed a significant reduction of the total HCsmostly methyl-branched chainsassociated with 100% insect mortality upon moulting to the next nymph stage. These results provided evidence on the essential role methyl-branched HCs play in the waterproofing properties of the cuticle (Moriconi et al, 2019). In this study, exposing CYP4G107-silenced insects to desiccation conditions affected significantly their survival, while CYP4G106 silencing had almost no effect on insect viability ( Fig.…”

“…The metabolic pathway to their formation involves the participation of fatty acid synthases (FASNs), the fatty acid elongation system, fatty acyl-CoA desaturases, fatty acyl-CoA reductases and cytochrome P450s of the 4G subfamily (Juárez et al, 1992;Juárez, 2004;Blomquist, 2010;Qiu et al, 2012). Integument FASNs have been shown to provide the longchain straight and methyl-branched fatty acyl precursors to HC formation in B. germanica (Juárez et al, 1992), in the fly Drosophila serrata (Chung et al, 2014), and in the kissing bugs T. infestans and Rhodnius prolixus (Juárez and Brenner, 1989;Moriconi et al, 2019). FASN products are substrates for a series of fatty acyl-CoA elongases (ELOVLs) involved in the formation of very-long-chain fatty acyl-CoAs from 18 to over 34 carbons in T. infestans (Juárez and Brenner, 1989;Juárez, 2004).…”

Advances in deciphering the genetic basis of insect cuticular hydrocarbon biosynthesis and variation

“…Interestingly, knockdown of four B. germanica FAS genes actually increased the total amount of CHCs, whereas only one of them, BgFas1, substantially decreased both n-alkanes and mb-CHCs (Pei et al 2019, Table 1). The above-mentioned examples indicate the challenges of transferring knowledge between taxa within the complicated phylogeny of the FAS gene family that has apparently undergone multiple duplications and neofunctionalizations (Finck et al 2016;Moriconi et al 2019). Their diverse functionalities are thereby far from restricted to CHC biosynthesis alone, but also include vital roles in lipogenesis, control of molting, and diapause induction (Tan et al 2017;Lammers et al 2019;Moriconi et al 2019).…”

“…The above-mentioned examples indicate the challenges of transferring knowledge between taxa within the complicated phylogeny of the FAS gene family that has apparently undergone multiple duplications and neofunctionalizations (Finck et al 2016;Moriconi et al 2019). Their diverse functionalities are thereby far from restricted to CHC biosynthesis alone, but also include vital roles in lipogenesis, control of molting, and diapause induction (Tan et al 2017;Lammers et al 2019;Moriconi et al 2019). This renders specifically characterizing and targeting FAS genes with a direct impact on CHC biosynthesis and diversification particularly difficult.…”

“…originate from a gene duplication in the Drosophila genus(Finck et al 2016;Moriconi et al 2019). In case of such a duplication event, it is difficult to infer what role the common ancestor of both genes played in CHC production.…”