Angiotensin-converting enzyme in Spodoptera littoralis: molecular characterization, expression and activity profile during development

Assessment of housekeeping genes stability for gene transcription regulation analysis of Spodoptera littoralis (Lepidoptera: Noctuidae) under Spodoptera littoralis nucleopolyhedrovirus viral infection

BACKGROUND

Normalization with respect to stable housekeeping genes is important to facilitate gene transcription regulation research and acquire more accurate quantitative polymerase chain reaction (qPCR) data. In the current study, five candidates housekeeping genes of the cotton leafworm, Spodoptera littoralis encoding for Actin (Actin), elongation factor 1-alpha (EF1α), ribosomal protein S3 (RPS3), ribosomal protein 49 (RP49), and Ubiquitin (Ubi), were evaluated as normalization housekeeping genes under Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) viral infection.

METHODS AND RESULTS

The qPCR results confirmed the expression of all five housekeeping genes in S. littoralis viral infected larvae. The expression profiles of the housekeeping genes showed that the EF1α, Actin, and RP49 had the minimum average Ct values of 18.41 ± 0.66, 18.84 ± 0.90 and 19.01 ± 0.87 in all infected samples, respectively. While RPS3 and Ubi showed the maximum average Ct of 21.61 ± 0.51 and 21.11 ± 0.82, respectively. According to the results of ΔCt and geNorm analysis, EF1α was ranked as the most stable housekeeping gene during infection time-course. While by using BestKeeper, geNorm and NormFinder, the Ubi, RP49, and RPS3 showed the most genes transcription stability. The obtained results were also validated using the Cytochrome c oxidase (COX) gene transcripts in response to SpliNPV infection.

CONCLUSIONS

The results revealed that EF1α and Ubi were the most stable housekeeping genes to be used for normalizing S. littoralis gene transcription regulation under SpliNPV infection. These findings, provide a significant addition for gene transcription regulation studies of S. littoralis upon infection using SpliNPV as a bio-agent.

Control of aging by the renin–angiotensin system: a review of C. elegans, Drosophila, and mammals

The free-living, non-parasitic nematode Caenorhabditis elegans is a premier model organism for the study of aging and longevity due to its short lifespan, powerful genetic tools, and conservation of fundamental mechanisms with mammals. Approximately 70 percent of human genes have homologs in C. elegans, including many that encode proteins in pathways that influence aging. Numerous genetic pathways have been identified in C. elegans that affect lifespan, including the dietary restriction pathway, the insulin/insulin-like growth factor (IGF) signaling pathway, and the disruption of components of the mitochondrial electron transport chain. C. elegans is also a powerful system for performing drug screens, and many lifespan-extending compounds have been reported; notably, several FDA-approved medications extend the lifespan in C. elegans, raising the possibility that they can also extend the lifespan in humans. The renin–angiotensin system (RAS) in mammals is an endocrine system that regulates blood pressure and a paracrine system that acts in a wide range of tissues to control physiological processes; it is a popular target for drugs that reduce blood pressure, including angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs). Emerging evidence indicates that this system influences aging. In C. elegans, decreasing the activity of the ACE homolog acn-1 or treatment with the ACE-inhibitor Captopril significantly extends the lifespan. In Drosophila, treatment with ACE inhibitors extends the lifespan. In rodents, manipulating the RAS with genetic or pharmacological interventions can extend the lifespan. In humans, polymorphisms in the ACE gene are associated with extreme longevity. These results suggest the RAS plays a conserved role in controlling longevity. Here, we review studies of the RAS and aging, emphasizing the potential of C. elegans as a model for understanding the mechanism of lifespan control.

Immune function of an angiotensin-converting enzyme against Rice stripe virus infection in a vector insect

Angiotensin-converting enzyme (ACE) plays diverse roles in the animal kingdom. However, whether ACE plays an immune function against viral infection in vector insects is unclear. In this study, an ACE gene (LsACE) from the small brown planthopper was found to respond to Rice stripe virus (RSV) infection. The enzymatic activities of LsACE were characterized at different pH and temperature. Twenty planthopper proteins were found to interact with LsACE. RSV infection significantly upregulated LsACE expression in the testicle and fat body. When the expression of LsACE in viruliferous planthoppers was inhibited, the RNA level of the RSV SP gene was upregulated 2-fold in planthoppers, and all RSV genes showed higher RNA levels in the rice plants consumed by these planthoppers, leading to a higher viral infection rate and disease rating index. These results indicate that LsACE plays a role in the immune response against RSV transmission by planthoppers.

Loss of angiotensin-converting enzyme-related (ACER) peptidase disrupts behavioural and metabolic responses to diet in Drosophila melanogaster

Drosophila Acer (Angiotensin-converting enzyme-related) encodes a member of the angiotensin-converting enzyme (ACE) family of metallopeptidases that in mammals play roles in the endocrine regulation of blood homeostasis. ACE is also expressed in adipose tissue, where it is thought to play a role in metabolic regulation. Drosophila ACER is expressed in the adult fat body of the head and abdomen and is secreted into the haemolymph. Acer null mutants have previously been found to have reduced night-time sleep and greater sleep fragmentation. ACER may thus be part of a signalling system linking metabolism with sleep. To further understand the role of ACER in response to diet, we measured sleep and other nutrient-responsive phenotypes in Acer null flies under different dietary conditions. We show that loss of Acer disrupts the normal response of sleep to changes in nutrition. Other nutrient-sensitive phenotypes, including survival and glycogen storage, were also altered in the Acer mutant but lipid storage was not. Although the physiological substrate of the ACER peptidase has not been identified, an alteration of the normal nutrient-dependent control of Drosophila insulin-like peptide 5 protein in the Acer mutant suggests insulin/IGF-like signalling as a candidate pathway modulated by ACER in the nutrient-dependent control of sleep, survival and metabolism.

Transcriptomic and Expression Analysis of the Salivary Glands in Brown Planthoppers, Nilaparvata lugens (Hemiptera: Delphacidae)

The brown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera: Delphacidae), is a serious rice pest because of its destructive feeding. The salivary glands of the BPH play a key role in successful feeding. In this study, we explored the salivary gland transcriptome (sialotranscriptome) of adult BPHs using Illumina sequencing and a total of 55,913 transcripts and 45,421 unigenes were obtained. We identified one reference gene RPL9 (Ribosomal protein L9) and 19 salivary protein genes from the BPH sialotranscripome, which were categorized as those involved in sugar metabolism, extra-oral digestion of cell wall components, detoxification, and suppression of plant defenses. Tissue expression profiles of 19 salivary protein genes analysis revealed that the expression level of alpha-glucosidase family 31 had no difference in five tissues, suggesting that it may have functions in the whole-body parts. Glucose dehydrogenase (flavine adenine dinucleotide, quinone)-like was expressed highly in the salivary gland, which might play putative role in insect feeding. Glucose dehydrogenase (acceptor) was expressed the highest level in head without salivary gland. Other salivary protein genes were highly expressed in gut or malpighian tubule, suggesting that they may play roles in digestive and detoxification mechanism. Moreover, we detected RPL9 is one of the genes that is most consistently present for acquisition of gene expression in different tissues. Thus, RPL9 can be a new reference for expression studies of BPH. The obtained BPH sialotranscripome provides a list of genes that have potential roles in feeding and interaction between BPHs and rice plants.

Transcriptome analysis of the salivary glands of the grain aphid, Sitobion avenae

Aphid saliva plays important roles in aphid-host interactions, such as assisting aphid digestion, detoxification, activating or suppressing plant defenses. The grain aphid, Sitobion avenae, is one of the most devastating pests of cereals worldwide. In this study, we performed the transcriptome analysis of salivary glands of S. avenae. A total of 33,079 assembled unigenes were identified in the salivary glands of aphids. Of the all obtained unigenes, 15,833(47.86%) and 10,829(32.73%) unigenes showed high similarity to known proteins in Nr and Swiss-Prot databases respectively. 526 unigenes were predicted to encode secretory proteins, including some digestive and detoxifying enzymes and potential effectors. The RT-PCR and RT-qPCR results showed that all of the 15 most highly expressed putative secretory proteins specifically expressed in salivary glands. Interestingly, 11 of the 15 most highly expressed putative secretory proteins were still not matched to function-known proteins. We also detected the expression of 9 interested putative secretory proteins in aphid different tissues, including some digestive and detoxifying enzymes, effectors and Ca2+ binding proteins. The results showed that only glutathione-S-transferase 1 was specifically expressed in salivary glands. These findings provide a further insight into the identification of potential effectors involving in aphid-cereals interactions.

The angiotensin converting enzyme (ACE) inhibitor, captopril disrupts the motility activation of sperm from the silkworm, Bombyx mori

Angiotensin I-converting enzyme (also known as peptidyl dicarboxypeptidase A, ACE, and EC 3.4.15.1), which is found in a wide range of organisms, cleaves C-terminal dipeptides from relatively short oligopeptides. Mammalian ACE plays an important role in the regulation of blood pressure. However, the precise physiological functions of insect ACE homologs have not been understood. As part of our effort to elucidate new physiological roles of insect ACE, we herein report a soluble ACE protein in male reproductive secretions from the silkmoth, Bombyx mori. Seminal vesicle sperm are quiescent in vitro, but vigorous motility is activated by treatment with either a glandula (g.) prostatica homogenate or trypsin in vitro. When seminal vesicle sperm were pre-incubated with captopril, a strong and specific inhibitor of mammalian ACE, and then stimulated to initiate motility by the addition of the g. prostatica homogenate or trypsin, the overall level of acquired motility was reduced in an inhibitor-concentration-dependent manner. In the course of this project, we detected ACE-related carboxypeptidase activity that was inhibited by captopril in both the vesicular (v.) seminalis of the noncopulative male reproductive tract and in the spermatophore that forms in the female bursa copulatrix at the time of mating, just as in an earlier report on the tomato moth, Lacanobia oleracea, which belongs to a different lepidopteran species (Ekbote et al., 2003a). Two distinct genes encoding ACE-like proteins were identified by analysis of B. mori cDNA, and were named BmAcer and BmAcer2, respectively [the former was previously reported by Quan et al. (2001) and the latter was first isolated in this paper]. RT-qPCR and Western blot analyses indicated that the BmAcer2 was predominantly produced in v. seminalis and transferred to the spermatophore during copulation, while the BmAcer was not detected in the adult male reproductive organs. A recombinant protein of BmAcer2 (devoid of a signal peptide) that was expressed in Escherichia coli cells exhibited captopril-sensitive carboxypeptidase activities. Our findings show that the BmAcre2 gene encodes a secreted ACE protein included in the Bombyx seminal plasma. In particular, the silkworm ACE protein in the seminal fluid might be involved in the signaling pathway that leads to the activation and regulation of sperm motility.

A quantitative peptidomics approach to unravel immunological functions of angiotensin converting enzyme in Locusta migratoria

Locusta migratoria angiotensin converting enzyme (LmACE) is encoded by multiple exons displaying variable number of genomic duplications. Treatments of lipopolysaccharide (LPS) as well as peptidoglycan but not β-1-3 glucan resulted in enhanced expression of angiotensin converting enzyme in hemocytes of Locusta migratoria. No such effect was observed in fat body cells. Differential peptidomics using locust plasma samples post infection with LPS in combination with both an LmACE transcript knockdown by RNAi and a functional knockdown using captopril allowed the identification of 5 circulating LPS induced peptides which only appear in the hemolymph of locust having full LmACE functionality. As these peptides originate from larger precursor proteins such as locust hemocyanin-like protein, having known antimicrobial properties, the obtained results suggest a possible direct or indirect role of LmACE in the release of these peptides from their precursors. Additionally, this experimental setup confirmed the role of LmACE in the clearance of multiple peptides from the hemolymph.

Transcriptomic and Expression Analysis of the Salivary Glands in White-Backed Planthoppers, Sogatella furcifera

The white-backed planthopper (WBPH), Sogatella furcifera (Horváth), is one of the serious rice pests because of its destructive feeding. The salivary glands of the WBPH play an important role in the feeding behaviour. Currently, however, very little is known about the salivary glands at the molecular level. We sequenced the salivary gland transcriptome (sialotranscripome) of adult WBPHs using the Illumina sequencing. A total of 65,595 transcripts and 51,842 unigenes were obtained from salivary glands. According to annotations against the Nr database, many of the unigenes identified were associated with the most studied enzymes in hemipteran saliva. In the present study, we identified 32 salivary protein genes from the WBPH sialotranscripome, which were categorized as those involved in sugar metabolism, detoxification, suppression of plant defense responses, immunity-related responses, general digestion, and other phytophagy processes. Tissue expression profiles analysis revealed that four of 32 salivary protein genes (multicopper oxidase 4, multicopper oxidase 6, carboxylesterase and uridine phosphorylase 1 isform X2) were primarily expressed in the salivary gland, suggesting that they played putative role in insect-rice interactions. 13 of 32 salivary protein genes were primarily expressed in gut, which might play putative role in digestive and detoxify mechanism. Development expression profiles analysis revealed that the expression level of 26 of 32 salivary protein genes had no significant difference, suggesting that they may play roles in every developmental stages of salivary gland of WBPH. The other six genes have a high expression level in the salivary gland of adult. 31 of 32 genes (except putative acetylcholinesterase 1) have no significant difference in male and female adult, suggesting that their expression level have no difference between sexes. This report analysis of the sialotranscripome for the WBPH, and the transcriptome provides a foundational list of the genes involved in feeding. Our data will be useful to investigate the mechanisms of interaction between the WBPH and the host plant.

Next Generation Sequencing Identifies Five Major Classes of Potentially Therapeutic Enzymes Secreted by Lucilia sericata Medical Maggots

Lucilia sericata larvae are used as an alternative treatment for recalcitrant and chronic wounds. Their excretions/secretions contain molecules that facilitate tissue debridement, disinfect, or accelerate wound healing and have therefore been recognized as a potential source of novel therapeutic compounds. Among the substances present in excretions/secretions various peptidase activities promoting the wound healing processes have been detected but the peptidases responsible for these activities remain mostly unidentified. To explore these enzymes we applied next generation sequencing to analyze the transcriptomes of different maggot tissues (salivary glands, gut, and crop) associated with the production of excretions/secretions and/or with digestion as well as the rest of the larval body. As a result we obtained more than 123.8 million paired-end reads, which were assembled de novo using Trinity and Oases assemblers, yielding 41,421 contigs with an N50 contig length of 2.22 kb and a total length of 67.79 Mb. BLASTp analysis against the MEROPS database identified 1729 contigs in 577 clusters encoding five peptidase classes (serine, cysteine, aspartic, threonine, and metallopeptidases), which were assigned to 26 clans, 48 families, and 185 peptidase species. The individual enzymes were differentially expressed among maggot tissues and included peptidase activities related to the therapeutic effects of maggot excretions/secretions.

Angiotensin-converting enzymes modulate aphid-plant interactions

Angiotensin-converting enzymes (ACEs) are key components of the renin–angiotensin system in mammals. However, the function of ACE homologs in insect saliva is unclear. Aphids presumably deliver effector proteins via saliva into plant cells to maintain a compatible insect–plant interaction. In this study, we showed that ACE modulates aphid–plant interactions by affecting feeding behavior and survival of aphids on host plants. Three ACE genes were identified from the pea aphid Acyrthosiphon pisum genome. ACE1 and ACE2 were highly expressed in the salivary glands and are predicted to function as secretory proteins. The ACE2 transcript level decreased in aphids fed on artificial diet compared with aphids fed on Vicia faba. The knockdown of the expression of each ACE by RNAi failed to affect aphid survival. When ACE1 and ACE2 were simultaneously knocked down, aphid feeding was enhanced. Aphids required less time to find the phloem sap and showed longer passive ingestion. However, the simultaneous knockdown of ACE1 and ACE2 resulted in a higher mortality rate than the control group when aphids were fed on plants. These results indicated that ACE1 and ACE2 function together to modulate A. pisum feeding and survival on plants.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

A conserved gene cluster as a putative functional unit in insect innate immunity

The Nimrod gene superfamily is an important component of the innate immune response. The majority of its member genes are located in close proximity within the Drosophila melanogaster genome and they lie in a larger conserved cluster ("Nimrod cluster"), made up of non-related groups (families, superfamilies) of genes. This cluster has been a part of the Arthropod genomes for about 300-350 million years. The available data suggest that the Nimrod cluster is a functional module of the insect innate immune response.

Identification and expression profile of Halloween genes involved in ecdysteroid biosynthesis in Spodoptera littoralis

20-Hydroxyecdyone (20E), an active form of ecdysteroid, is the key hormone in insect growth and development. The biosynthesis of ecdysteroid is triggered and under the control of the neuropeptide, prothoracicotropic hormone (PTTH). To date, five cytochrome P450 enzymes, namely Spook (Spo), Phantom (Phm), Disembodied (Dib), Shadow (Sad) and Shade (Shd) related to ecdysteroid biosynthesis, are identified and the character of last four enzymes is well studied in Drosophila melanogaster, Bombyx mori and Manduca sexta. These genes are called Halloween genes and mediate the biosynthesis of 20E from cholesterol. In this study, we extended these works to a major pest insect in agriculture, the cotton leafworm Spodoptera littoralis (Lepidoptera: Noctuidae). We identified the sequence of five Halloween genes, and the converted amino acid sequences were compared with those of other insects. The phylogenetic analysis clearly showed separated clusters of each gene and the evolutional conservation in insects with a high similarity in Lepidoptera. Spo, phm, dib and sad were predominantly expressed in prothoracic glands, and shd was expressed in fat body and Malpighian tubules at the last instar larvae. Spo expression was kept high level between day 2 and day 4 after ecdysis. The expression of phm and dib peaked at day 2, and sad and shd expressions peaked at day 2 and day 4 after ecdysis. In addition, the hemolymph ecdysteroid titer showed a small peak at day 2 and a large peak at day 4 after ecdysis. These results suggest the importance of Halloween genes in ecdysone biosynthesis by prothoracic glands and conversion of ecdysone into 20E by fat body in larval-pupal metamorphosis.

The secreted salivary proteome of the pea aphid Acyrthosiphon pisum characterised by mass spectrometry

Nine proteins secreted in the saliva of the pea aphid Acyrthosiphon pisum were identified by a proteomics approach using GE-LC-MS/MS and LC-MS/MS, with reference to EST and genomic sequence data for A. pisum. Four proteins were identified by their sequences: a homolog of angiotensin-converting enzyme (an M2 metalloprotease), an M1 zinc-dependant metalloprotease, a glucose-methanol-choline (GMC)-oxidoreductase and a homolog to regucalcin (also known as senescence marker protein 30). The other five proteins are not homologous to any previously described sequence and included an abundant salivary protein (represented by ACYPI009881), with a predicted length of 1161 amino acids and high serine, tyrosine and cysteine content. A. pisum feeds on plant phloem sap and the metalloproteases and regucalcin (a putative calcium-binding protein) are predicted determinants of sustained feeding, by inactivation of plant protein defences and inhibition of calcium-mediated occlusion of phloem sieve elements, respectively. The amino acid composition of ACYPI009881 suggests a role in the aphid salivary sheath that protects the aphid mouthparts from plant defences, and the oxidoreductase may promote gelling of the sheath protein or mediate oxidative detoxification of plant allelochemicals. Further salivary proteins are expected to be identified as more sensitive MS technologies are developed.

Effect of ace inhibitors and TMOF on growth, development, and trypsin activity of larval Spodoptera littoralis

Angiotensin converting enzyme (ACE) is a zinc metallopeptidase capable of cleaving dipeptide or dipeptideamide moieties at the C-terminal end of peptides. ACE is present in the hemolymph and reproductive tissues of insects. The presence of ACE in the hemolymph and its broad substrate specificity suggests an important role in processing of bioactive peptides. This study reports the effects of ACE inhibitors on larval growth in the cotton leafworm Spodoptera littoralis. Feeding ACE inhibitors ad lib decreased the growth rate, inhibited ACE activity in the larval hemolymph, and down-regulated trypsin activity in the larval gut. These results indicate that S. littoralis ACE may influence trypsin biosynthesis in the larval gut by interacting with a trypsin-modulating oostatic factor (TMOF). Injecting third instar larvae with a combination of Aea-TMOF and the ACE inhibitor captopril, down-regulated trypsin biosynthesis in the larval gut indicating that an Aea-TMOF gut receptor analogue could be present. Injecting captopril and enalapril into newly molted fifth instar larvae stopped larval feeding and decreased weight gain. Together, these results indicate that ACE inhibitors are efficacious in stunting larval growth and ACE plays an important role in larval growth and development.