An Insight into the Transcriptome of the Digestive Tract of the Bloodsucking Bug, Rhodnius prolixus

Abstract

The bloodsucking hemipteran Rhodnius prolixus is a vector of Chagas' disease, which affects 7–8 million people today in Latin America. In contrast to other hematophagous insects, the triatomine gut is compartmentalized into three segments that perform different functions during blood digestion. Here we report analysis of transcriptomes for each of the segments using pyrosequencing technology. Comparison of transcript frequency in digestive libraries with a whole-body library was used to evaluate expression levels. All classes of digestive enzymes were highly expressed, with a predominance of cysteine and aspartic proteinases, the latter showing a significant expansion through gene duplication. Although no protein digestion is known to occur in the anterior midgut (AM), protease transcripts were found, suggesting secretion as pro-enzymes, being possibly activated in the posterior midgut (PM). As expected, genes related to cytoskeleton, protein synthesis apparatus, protein traffic, and secretion were abundantly transcribed. Despite the absence of a chitinous peritrophic membrane in hemipterans - which have instead a lipidic perimicrovillar membrane lining over midgut epithelia - several gut-specific peritrophin transcripts were found, suggesting that these proteins perform functions other than being a structural component of the peritrophic membrane. Among immunity-related transcripts, while lysozymes and lectins were the most highly expressed, several genes belonging to the Toll pathway - found at low levels in the gut of most insects - were identified, contrasting with a low abundance of transcripts from IMD and STAT pathways. Analysis of transcripts related to lipid metabolism indicates that lipids play multiple roles, being a major energy source, a substrate for perimicrovillar membrane formation, and a source for hydrocarbons possibly to produce the wax layer of the hindgut. Transcripts related to amino acid metabolism showed an unanticipated priority for degradation of tyrosine, phenylalanine, and tryptophan. Analysis of transcripts related to signaling pathways suggested a role for MAP kinases, GTPases, and LKBP1/AMP kinases related to control of cell shape and polarity, possibly in connection with regulation of cell survival, response of pathogens and nutrients. Together, our findings present a new view of the triatomine digestive apparatus and will help us understand trypanosome interaction and allow insights into hemipteran metabolic adaptations to a blood-based diet.

Caste-specific and sex-specific expression of chemoreceptor genes in a termite

“…Peptide sequences of chemoreceptors and binding proteins of the following species were obtained from NCBI, and used as BLAST queries for our peptide database with an E-value cutoff of 1E−7: Z. nevadensis [14], P. americana [34], T. castaneum [31,35,23], H. oblita [36], D. ponderosae [37], A. mellifera [38,39], D. melanogaster [17,[40][41][42][43], A. gambiae [44], A. aegypti [45], A. lineolatus [46], R. prolixus [47], L. migratria [48], and B. mori [30,49,50]. The peptide sequences of ORs of M. caryae were translated from the nucleotide sequences [51] using the Nucleotide Sequence Translation tool (EMBL-EBI, http://www.ebi.ac.uk/Tools/st/).…”

Evolution of hematophagous habit in Triatominae (Heteroptera: Reduviidae)

“…The majority of the predator reduvid bites are very painful for vertebrates due to their markedly proteolytic saliva, which is fundamental for them to paralyze and digest their invertebrate prey. The presence of trypsin transcripts in the sialome of T. infestans and Panstrongylus geniculatus (Latreille) suggests a role for these molecules very different from the digestive one (Ribeiro et al 2014). In the same way, it is interesting from the point of view of the evolution of the predator habit to hematophagy that a paralyzing protein has been detected in the saliva of T. infestans, a function previously only found in predator insects (Alves et al 2011).…”

“…The phytophagous ancestors of the early reduvids lost their ability to use trypsin, the common digestive protease, because plant sap is virtually without protein and the seeds have strong antitrypsins (Savelkoul et al 1992;Lehane 2005). In the same way the predator reduvids and the hematophagous triatomines developed the capacity to secrete catepsins in the intestine to digest the proteins found most abundantly in their food (Lehane 2005;Ribeiro et al 2014). The catepsins are a family of proteases normally found in the intracellular lysosomes, which generally become active at low pH (best 5.5 to 6), so that it can be said that the triatomines developed a system to acidify lightly alkaline blood (pH ≈ 7.4) (Terra et al 1996).…”

“…The catepsins are a family of proteases normally found in the intracellular lysosomes, which generally become active at low pH (best 5.5 to 6), so that it can be said that the triatomines developed a system to acidify lightly alkaline blood (pH ≈ 7.4) (Terra et al 1996). The finding of proteases (trypsins) in the rectal ampulla of R. prolixus is congruent with the loss of their digestive function in triatomines (Ribeiro et al 2014). …”

Pathways of Insect Protein Digestion: Triatominae (Kissing Bugs)

“…For example, it is quite possible that there are further types of luminal digestive enzymes waiting to be discovered in triatomines. A recent transcriptome analysis of the R. prolixus intestine has revealed many genes related to digestive physiology including digestive enzymes lacking some amino acid residues important for enzymatic activity [24]. Furthermore, it would be very important to know whether or not microbiota plays a role in the digestion of triatomines and how strong the influence of T. cruzi on the digestive system might be.…”