Activation of the Ae4 (Slc4a9) cation-driven Cl-/HCO3- exchanger by the cAMP-dependent protein kinase in salivary gland acinar cells

Ae4 transporters are critical for Cl- uptake across the basolateral membrane of acinar cells in the submandibular gland (SMG). Although required for fluid secretion, little is known about the physiological regulation of Ae4. To investigate whether Ae4 is regulated by the cAMP-dependent signaling pathway, we measured Cl-/HCO3- exchanger activity in SMG acinar cells from Ae2-/- mice, which only express Ae4, and found that the Ae4-mediated activity was increased in response to β-adrenergic receptor stimulation. Moreover, pretreatment with H89, an inhibitor of the cAMP-activated kinase (PKA), prevented the stimulation of Ae4 exchangers. We then expressed Ae4 in CHO-K1 cells and found that the Ae4-mediated activity was increased when Ae4 is coexpressed with the catalytic subunit of PKA (PKAc), which is constitutively active. Ae4 sequence analysis showed two potential PKA phosphorylation serine residues located at the intracellular NH2-terminal domain according to a homology model of Ae4. NH2-terminal domain Ser residues were mutated to alanine (S173A and S273A, respectively), where the Cl-/HCO3- exchanger activity displayed by the mutant S173A was not activated by PKA. Conversely, S273A mutant kept the PKA dependency. Together, we conclude that Ae4 is stimulated by PKA in SMG acinar cells by a mechanism that probably depends on the phosphorylation of S173.NEW & NOTEWORTHY We found that Ae4 exchanger activity in secretory salivary gland acinar cells is increased upon β-adrenergic receptor stimulation. The activation of Ae4 was prevented by H89, a nonselective PKA inhibitor. Protein sequence analysis revealed two residues (S173 and S273) that are potential targets of cAMP-dependent protein kinase (PKA). Experiments in CHO-K1 cells expressing S173A and S273A mutants showed that S173A, but not S273A, is not activated by PKA.

Expression Profiles of Digestive Genes in the Gut and Salivary Glands of Tarnished Plant Bug (Hemiptera: Miridae)

Host plant preference of agricultural pests may shift throughout the growing season, allowing the pests to persist on wild hosts when crops are not available. Lygus Hahn (Hemiptera: Miridae) bugs are severe pests of cotton during flowering and fruiting stages, but can persist on alternative crops, or on weed species. Diversity of digestive enzymes produced by salivary glands and gut tissues play a pivotal role in an organism's ability to utilize various food sources. Polyphagous insects produce an array of enzymes that can process carbohydrates, lipids, and proteins. In this study, the digestive enzyme repertoire of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was identified by high-throughput sequencing followed by cDNA cloning and sequencing. This study identified 87 digestive genes, including 30 polygalacturonases (PG), one β-galactosidase, three α-glucosidases, six β-glucosidases, 28 trypsin-like proteases, three serine proteases, one apyrase-like protease, one cysteine protease, 12 lipases, and two transcripts with low similarity to a xylanase A-like genes. RNA-Seq expression profiles of these digestive genes in adult tarnished plant bugs revealed that 57 and 12 genes were differentially expressed in the salivary gland and gut (≥5-fold, P ≤ 0.01), respectively. All polygalacturonase genes, most proteases, and two xylanase-like genes were differentially expressed in salivary glands, while most of the carbohydrate and lipid processing enzymes were differentially expressed in the gut. Seven of the proteases (KF208689, KF208697, KF208698, KF208699, KF208700, KF208701, and KF208702) were not detected in either the gut or salivary glands.

An Aphid-Secreted Salivary Protease Activates Plant Defense in Phloem

Recent studies have reported that aphids facilitate their colonization of host plants by secreting salivary proteins into host tissues during their initial probing and feeding. Some of these salivary proteins elicit plant defenses, but the molecular and biochemical mechanisms that underlie the activation of phloem-localized resistance remain poorly understood. The aphid Myzus persicae, which is a generalized phloem-sucking pest, encompasses a number of lineages that are associated with and adapted to specific host plant species. The current study found that a cysteine protease Cathepsin B3 (CathB3), and the associated gene CathB3, was upregulated in the salivary glands and saliva of aphids from a non-tobacco-adapted (NTA) aphid lineage, when compared to those of a tobacco-adapted lineage. Furthermore, the knockdown of CathB3 improved the performance of NTA lineages on tobacco, and the propeptide domain of CathB3 was found to bind to tobacco cytoplasmic kinase ENHANCED DISEASE RESISTANCE 1-like (EDR1-like), which triggers the accumulation of reactive oxygen species in tobacco phloem, thereby suppressing both phloem feeding and colonization by NTA lineages. These findings reveal a novel function for a cathepsin-type protease in aphid saliva that elicits effective host plant defenses and warranted the theory of host specialization for generalist aphids.

Extraoral digestion: outsourcing the role of the hemipteran midgut

Extraoral digestion allows for breakdown of dietary components before they reach the midgut for final enzymatic degradation and absorption. In the Hemiptera, this is achieved by the secretion of enzyme-rich fluids from the salivary gland, with the combination of protein and mRNA from these tissues termed the sialome. Separate channels within the hemipteran stylets allow for secretion of saliva and ingestion of predigested material in a non-reflux mechanism. Both feeding mode and diet type influence the composition of the hemipteran sialome, as illustrated by 1) differences in protease abundance between hematophagous and predatory heteropteran sialomes, 2) diet specific aminopeptidase-N genes among aphid biotypes, and 3) adaptation-induced sialome variation in related cicada populations. Despite challenges associated with incomplete genome annotation, -omics analysis of the sialomes of diverse hemipteran species will enhance understanding of both sialome function and the evolution of extraoral digestion within the order.

Proteases and nucleases across midgut tissues of Nezara viridula (Hemiptera:Pentatomidae) display distinct activity profiles that are conserved through life stages

The southern green stink bug, Nezara viridula is a polyphagous pest of commercially important crops during both nymph and adult stages. This insect has recently transitioned from a secondary agricultural pest to one of primary concern. Novel management solutions are needed due to the limited effectiveness of current control strategies. We performed biochemical and transcriptomic analyses to characterize digestive enzymes in the salivary glands and along midgut tissues of N. viridula nymphs and adults fed on sweet corn. The digestive profiles were more distinct between midgut regions (M1 to M3) than between life stages. Aminopeptidase and chymotrypsin activities declined from the M1 (anterior) toward the M3 midgut region. Cysteine protease activity was higher in the M2 and M3 regions than in M1. Differences in sensitivity to chymotrypsin inhibitors between midgut regions suggest that distinct genes or isoforms are expressed in different regions of the gut. In nymphs, DNA and RNA degradation was higher in M1 than in M3. Adult nuclease activity was low across all midgut regions, but high in salivary glands. The differences in protease activities are reflected by transcriptomic data and functional enrichment of GO terms. Together, our results show that different regions of the digestive tract of N. viridula have specific and distinct digestive properties, and increase our understanding of the physiology of this organism.

Malaria load affects the activity of mosquito salivary apyrase

Mosquitoes infected by sporozoites, the infectious stage of malaria, bite more frequently than uninfected mosquitoes. One of the mechanisms underlying this behavioural change appears to be that the sporozoites decrease the activity of apyrase, an ADP-degrading enzyme that helps the mosquitoes to locate blood. Using the parasite Plasmodium berghei and the mosquito Anopheles gambiae, we confirmed that sporozoite infection alters the host-seeking behaviour of mosquitoes by making them more likely to refeed after a first blood meal, and that apyrase activity is one of the mechanisms of the increased biting persistence and motivation of infectious mosquitoes. We further showed that apyrase activity decreases as the sporozoite load increases, and that mosquitoes with lower apyrase activity take up less blood, making it more likely that they would return to top up their blood meal. Finally, by comparing full-sib families of mosquitoes, we showed that there was genetic variation for apyrase activity, but not for the resistance of parasites to be manipulated. Our results give new insights in understanding how malaria parasites change their hosts to affect their own transmission.

Herbivorous Caterpillars Can Utilize Three Mechanisms to Alter Green Leaf Volatile Emission

Green plants emit green leaf volatiles (GLVs) as a general damage response. These compounds act as signals for the emitter plant, neighboring plants, and even for insects in the ecosystem. However, when oral secretions from certain caterpillars are applied to wounded leaves, GLV emissions are significantly decreased or modified. We examined four caterpillar species representing two lepidopteran families for their capacity to decrease GLV emissions from Zea mays leaf tissue. We also investigated the source of the GLV modifying components in the alimentary tract of the various caterpillars. In Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae), Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), and Manduca sexta (Linnaeus) (Lepidoptera: Sphingidae), we found three distinct mechanisms to modify GLV emission: a heat-stable compound in the gut, a heat-labile enzyme in salivary gland homogenate (previously described in Bombyx mori (Linnaeus) (Lepidoptera: Bombycidae), and an isomerase in the salivary gland homogenate, which catalyzes the conversion of (Z)-3-hexenal to (E)-2-hexenal (previously described in M. sexta). These mechanisms employed by caterpillars to suppress or modify GLV emission suggest a counteraction against the induced indirect volatile defenses of a plant and provides further insights into the ecological functions of GLVs.

Tissue-specific transcription of proteases and nucleases across the accessory salivary gland, principal salivary gland and gut of Nezara viridula

The phytophagous stink bug, Nezara viridula (L.) infests multiple plant species and impacts agricultural production worldwide. We analyzed the transcriptomes of N. viridula accessory salivary gland (ASG), principal salivary gland (PSG) and gut, with a focus on putative digestive proteases and nucleases that present a primary obstacle for the stability of protein- or nucleic acid-based stink bug control approaches. We performed high throughput Illumina sequencing followed by de novo transcriptome assemblies. We identified the sequences of 141 unique proteases and 134 nucleases from the N. viridula transcriptomes. Analysis of relative transcript abundance in conjunction with previously reported proteome data (Lomate and Bonning, 2016) supports high levels of serine protease expression in the salivary glands and high cysteine protease expression in the gut. Specifically, trypsin and chymotrypsin transcripts were abundant in the PSG, and cathepsin L-like cysteine protease transcripts were abundant in the gut. Nuclease transcript levels were generally lower than those of the proteases, the exception being abundant transcripts of ribonuclease-C20 in the PSG. The abundance of chymotrypsin, trypsin, and some carboxypeptidase transcripts suggests a significant role for the PSG in production of digestive enzymes. This result is at odds with the premise that the ASG produces watery saliva, which is high in enzymatic activity, while the PSG produces only sheath saliva. We have generated a comprehensive transcriptome sequence dataset from the digestive organs of N. viridula, identified major protease and nuclease genes and confirmed expression of the most abundant enzymes thereby providing greater insight into the digestive physiology of N. viridula.

Molecular and biochemical characterization of the bed bug salivary gland cholinesterase as an acetylcholine-sequestering enzyme

The common bed bug, Cimex lectularius, possesses a cholinesterase expressed exclusively in the salivary gland (ClSChE). In this study, we investigated the molecular forms, tissue distribution patterns and biochemical properties of ClSChE and showed that ClSChE exists as a soluble monomeric form or a soluble dimeric form connected by a disulfide bridge. Immunohistochemical analysis confirmed that ClSChE was expressed in the epithelial cells of both the salivary gland and the duct. In addition, the secretion of monomeric ClSChE through the proboscis during feeding was confirmed by western blotting using a ClSChE-specific antibody. To predict the role of ClSChE injected into the tissue of an animal host, we analyzed the extent of hydrolysis of acetylcholine (ACh) by ClSChE by ultra-performance liquid chromatography-tandem mass spectrometry. ClSChE binding to ACh was not clearly resolved in the binding assay format used in this study, probably due to the weak but detectable ACh-hydrolytic activity of ClSChE. Nevertheless, kinetic analysis revealed that ClSChE possesses extremely low K_m (high affinity to ACh) and V_max values. These findings suggest that ClSChE functions virtually as an ACh-sequestering protein by having a very strong affinity to ACh but an extremely long turnover time. Given that ACh regulates a wide variety of host physiologies, we discuss the tentative roles of ClSChE in blood vessel constriction and itch/pain regulation in the host.

Human Kallikrein 6 Expression in Salivary Gland Tumors

Human kallikrein 6 (hK6), also known as zyme/protease M/neurosin), is expressed in many normal glandular tissues. The aim of this study was to determine whether hK6 is expressed in salivary gland tissues and salivary gland tumors (both benign and malignant), using an immunohistochemical method. Pleomorphic adenomas (PA), adenoid cystic carcinomas, polymorphous low-grade adenocarcinomas, acinic cell carcinomas, mucoepidermoid carcinomas, and adenocarcinomas not otherwise specified of both minor and major salivary glands were examined. Cells lining duct-like structures and non-duct-like cells were scored. Only in PA of minor salivary gland origin was overall staining higher in duct-like than in non-duct-like cells. In all other tumors exhibiting both types of cells, hK6 staining was similar in both duct-like and non-duct-like cells. Tumors that exhibited non-duct-like cells only also exhibited cytoplasmic staining. Results of this study show that salivary gland tumors express hK6, apparently downregulated in comparison with normal salivary gland tissue, and that this expression is not specific for any of the tumors studied.

Tick Salivary Cholinesterase: A Probable Immunomodulator of Host-parasite Interactions

The southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), is the most economically important cattle ectoparasite in the world. Rhipicephalus microplus and Rhipicephalus annulatus (Say) continue to threaten U.S. cattle producers despite eradication and an importation barrier based on inspection, dipping of imported cattle in organophosphate (OP) acaricide, and quarantine of infested premises. OP acaricides inhibit acetylcholinesterase (AChE), essential to tick central nervous system function. Unlike vertebrates, ticks possess at least three genes encoding AChEs, differing in amino acid sequence and biochemical properties. Genomic analyses of R. microplus and the related tick, Ixodes scapularis, suggest that ticks contain many genes encoding different AChEs. This work is the first report of a salivary cholinesterase (ChE) activity in R. microplus, and discusses complexity of the cholinergic system in ticks and significance of tick salivary ChE at the tick-host interface. It further provides three hypotheses that the salivary ChE plausibly functions 1) to reduce presence of potentially toxic acetylcholine present in the large bloodmeal imbibed during rapid engorgement, 2) to modulate the immune response (innate and/or acquired) of the host to tick antigens, and 3) to influence transmission and establishment of pathogens within the host animal. Ticks are vectors for a greater number and variety of pathogens than any other parasite, and are second only to mosquitoes (owing to malaria) as vectors of serious human disease. Saliva-assisted transmission (SAT) of pathogens is well-known; however, the salivary components participating in the SAT process remain to be elucidated.

[Expression of midkine and microvessel density in salivary adenoid cystic carcinoma]

OBJECTIVE

This study aimed to investigate the expression of midkine (MK) and microvessel density (MVD) in patients with salivary adenoid cystic carcinoma (SACC) and its clinical significance, as well as detect the correlation between the expression of MK and MVD in SACC.

METHODS

Immunohistochemistry analysis (SP method) for MK and MVD were performed on 60 cases of SACC and 26 cases of normal salivary gland tissue. The expression of MK and MVD, as well as the correlation between the expression of MK and MVD in SACC were detected.

RESULTS

In SACC, the MK expression rate was 70.0% (42/60), and MK was not expressed in normal tissue. Statistical significance was found between SACC and normal tissue (P<0.05). The MVD values in SACC and normal salivary gland tissues were 38.73 +/- 8.96 and 11.15 +/- 3.33, respectively. These values were statistically significant (P<0.05). The expression levels of MK and MVD were unrelated to age, gender, and type in SACC (P>0.05), but correlated with tumor size, lymph node metastasis, and tumor-node-metastasis in SACC (P<0.05). The expression of MK and MVD was positively correlated with SACC (r=0.560, P<0.05).

CONCLUSION

SACC is correlated with the expression of MK protein and the increase in MVD, which may be some of the early diagnostic markers in SACC.

The Significance of Matrix Metalloproteinases in Oral Diseases

Matrix metalloproteinases (MMPs) belong to a family of structurally related zinc-dependent proteolytic enzymes that are known to play a key role in the catabolic turnover of extracellular matrix (ECM) components. Research studies to date have indicated that MMPs regulate the activity of several non-ECM bioactive substrates, including growth factors, cytokines, chemokines and cell receptors, which determine the tissue microenvironment. Disruption of the balance between the concentration of active matalloproteinases and their inhibitors (TIMPs) may lead to pathological changes associated with uncontrolled ECM turnover, tissue remodeling, inflammatory response, cell growth and migration. This brief review presents some information on MMPs' role in inflammatory, metabolic and cancer abnormalities related to the salivary glands, as well as MMP-related aspects that lead to the formation of human dentinal caries lesions. In oral diseases, the most relevant biological fluid commonly used for diagnosing periodontal diseases is saliva. In diseased patients with significantly higher levels of MMPs in their saliva than healthy people, most extracellular matrix components undergo digestion to lower molecular weight forms. Conventional treatment successfully reduces the levels of MMPs inhibits the progressive breakdown of gingival and periodontal ligament collagens. Beside inflammatory abnormalities like Sjögren's syndrome (SS), a large group of disorders is comprised of cancers, most of them involving the parotid gland.

Identification of Genes Potentially Responsible for extra-Oral Digestion and Overcoming Plant Defense from Salivary Glands of the Tarnished Plant Bug (Hemiptera: Miridae) Using cDNA Sequencing

Saliva is known to play a crucial role in tarnished plant bug (TPB, Lygus lineolaris [Palisot de Beauvois]) feeding. By facilitating the piercing, the enzyme-rich saliva may be used for extra-oral digestion and for overcoming plant defense before the plant fluids are ingested by TPBs. To identify salivary gland genes, mRNA was extracted from salivary glands and cDNA library clones were sequenced. A de novo-assembling of 7,000 Sanger sequences revealed 666 high-quality unique cDNAs with an average size of 624 bp, in which the identities of 347 cDNAs were determined using Blast2GO. Kyoto Encyclopedia of Genes and Genomes analysis indicated that these genes participate in eighteen metabolic pathways. Identifications of large number of enzyme genes in TPB salivary glands evidenced functions for extra-oral digestion and feeding damage mechanism, including 45 polygalacturonase, two α- amylase, one glucosidase, one glycan enzyme, one aminopeptidase, four lipase, and many serine protease cDNAs. The presence of multiple transcripts, multigene members, and high abundance of cell wall degradation enzymes (polygalacturonases) indicated that the enzyme-rich saliva may cause damage to plants by breaking down plant cell walls to make nutrients available for feeding. We also identified genes potentially involved in insect adaptation and detoxifying xenobiotics that may allow insects to overcome plant defense responses, including four glutathione S-transferases, three esterases, one cytochrome P450, and several serine proteases. The gene profiles of TPB salivary glands revealed in this study provides a foundation for further understanding and potential development of novel enzymatic inhibitors, or other RNAi approaches that may interrupt or minimize TPB feeding damage.

An insight into the functional role of thioredoxin reductase, a selenoprotein, in maintaining normal native microbiota in the Gulf Coast tick (Amblyomma maculatum)

Tick selenoproteins have been associated with antioxidant activity in ticks. Thioredoxin reductase (TrxR), also a selenoprotein, belongs to the pyridine nucleotide-disulphide oxidoreductase family of proteins and is an important antioxidant. Molecular interactions between native microbiota and tick hosts have barely been investigated to date. In this study, we determined the functional role of TrxR in tick feeding and in maintenance of the native microbial community. TrxR transcript levels remained high and microbial load was reduced throughout tick attachment to the vertebrate host. RNA interference (RNAi) showed that depletion of TrxR activity did not interfere with tick haematophagy or phenotype but did reduce the viability of the microbiome within the tick tissues, presumably by perturbing redox homeostasis. The transcriptional activity of various antioxidant genes remained unaffected whereas the antioxidant genes Manganese superoxide dismutase (MnSOD), copper/zinc superoxide dismutase (Cu/Zn SOD) and selenoprotein M (SelM) were significantly down-regulated in salivary glands of the ticks subjected to RNAi. The perturbed TrxR enzymatic activity in the knocked-down tick tissues negatively affected the bacterial load as well. Furthermore, we observed the altered bacterial profiles in TrxR-silenced tick tissues. Taken together, these results indicate an essential functional role for TrxR in maintaining the bacterial community associated with ticks.

Molecular Characterization and Expression Profiles of Polygalacturonase Genes in Apolygus lucorum (Hemiptera: Miridae)

Polygalacturonase (PG) is an enzyme in the salivary glands of piercing-sucking mirid bugs (Hemiptera: Miridae) that plays a key role in plant feeding and injury. By constructing a full-length cDNA library, we cloned and characterized 14 PG genes from the salivary glands of Apolygus lucorum, a pestiferous mirid bug in cotton, fruit trees and other crops in China. BLAST search analysis showed that the amino acid sequences deduced from transcripts of the PG genes were closely related to PGs from other mirid bugs. Phylogenetic analysis showed that the PGs of mirid bugs had six main branches, PG1-PG6 (Genbank accession numbers: KF881899~KF881912). We investigated the mRNA expression patterns of the A. lucorum PG genes using real-time PCR. All 14 PGs were expressed significantly higher in the salivary glands than in other tissues (head, thorax, abdomen, leg and wing). For eggs and nymphs, the expression levels of these PGs were much higher in the 5th instar stage than in the egg, and 1st and 3rd instar stages. The PG expression levels in 1-day-old adults were very low, and increased in 5, 20 and 30-day-old adults. Additionally, PG expression levels were generally similar between males and females. The possible physiological functions of PGs in A. lucorum were discussed.

Reprolysin metalloproteases from Ixodes persulcatus, Rhipicephalus sanguineus and Rhipicephalus microplus ticks

Metalloproteases (MPs) have been considered essential for blood feeding and other physiological functions in several hematophagous animals, including ticks. We report the characterization of MP sequences of three important ticks from Asia, Africa and America: Ixodes persulcatus (Ip-MPs), Rhipicephalus sanguineus (Rs-MPs) and R. microplus (BrRm-MPs). Amino acid sequence identity between R. microplus and R. sanguineus MPs ranged from 76 to 100 %, and identities among I. persulcatus, I. ricinus and I. scapularis MP sequences ranged from 88 to 97 %. This high sequence identity and typical functional motifs show that all sequences are MPs. The presence of a zinc binding site, a Met-turn and cysteine rich domain at the C-terminal region indicates that these proteins belong to the reproplysin family of MPs. Differences in amino acid sequences of BrRm-MP1, BrRm-MP2, BrRm-MP4 and BrRm-MP5 (from Porto Alegre strain ticks) were 6, 2, 7 and 5 %, respectively, when compared with sequences deposited in GenBank for the same genes from other R. microplus isolates. Analyses of MPs predicted that they have various highly antigenic regions. Semi-quantitative RT-PCR analysis revealed the presence of transcripts in salivary glands of partially and fully fed female ticks. None of these transcripts were observed in males (except BrRm-MP4) and eggs. These enzymes may be functional components required during tick feeding to manipulate host defenses and support tick hematophagy.

Molecular characterization of soluble and membrane-bound trehalases of the whitefly, Bemisia tabaci

Trehalases (Tres) have been demonstrated to be the key enzymes that are involved in various trehalose-associated physiological processes in insects. However, little attention has been devoted to the Tres in the whitefly, Bemisia tabaci. In this study, a soluble Tre (BtTre-1) and a membrane-bound Tre (BtTre-2) were cloned in the invasive cryptic species Middle East-Asia Minor 1 (MEAM1) of the whitefly B. tabaci complex. Alignment of deduced amino acids sequences of both BtTres revealed that they share common consensus regions and residues with Tres of other insect species. Levels of BtTres expression in various stages and tissues of the whitefly suggested that BtTre-2 may play a key role in trehalose catabolism during development of the whitefly, especially for oocyte development, while BtTre-1 may prevent trehalose in salivary gland from leaking and entering into plants along with saliva. Potential roles of trehalose catabolism in response to direct and/or plant-mediated indirect effects of Tomato Yellow Leaf Curl China Virus (TYLCCNV) were also detected. Whiteflies feeding on virus-infected tobacco plants showed higher BtTres expressions and accordingly higher BtTres activity but lower trehalose content than those feeding on uninfected plants. The enhanced trehalose catabolism may be beneficial to oocyte development in ovary and attenuate plant defensive responses induced by trehalose in saliva. Viruliferous and nonviruliferous whiteflies feeding on cotton, a nonhost plant for TYLCCNV, differed significantly only in trehalose content. The higher trehalose content in viruliferous whiteflies may be conducive to resisting the stress inflicted by TYLCCNV.

Carbohydrases in the digestive system of the spined soldier bug, Podisus maculiventris (Say) (Hemiptera: Pentatomidae)

The spined soldier bug, Podisus maculiventris, is a generalist predator of insects and has been used in biological control. However, information on the digestion of food in this insect is lacking. Therefore, we have studied the digestive system in P. maculiventris, and further characterized carbohydrases in the digestive tract. The midgut of all developmental stages was composed of anterior, median, and posterior regions. The volumes of the anterior midgut decreased and the median midgut increased in older instars and adults, suggesting a more important role of the median midgut in food digestion. However, carbohydrase activities were predominant in the anterior midgut. In comparing the specific activity of carbohydrases, α-amylase activity was more in the salivary glands (with two distinct activity bands in zymograms), and glucosidase and galactosidase activities were more in the midgut. Salivary α-amylases were detected in the prey hemolymph, demonstrating the role of these enzymes in extra-oral digestion. However, the catalytic efficiency of midgut α-amylase activity was approximately twofold more than that of the salivary gland enzymes, and was more efficient in digesting soluble starch than glycogen. Midgut α-amylases were developmentally regulated, as one isoform was found in first instar compared to three isoforms in fifth instar nymphs. Starvation significantly affected carbohydrase activities in the midgut, and acarbose inhibited α-amylases from both the salivary glands and midgut in vitro and in vivo. The structural diversity and developmental regulation of carbohydrases in the digestive system of P. maculiventris demonstrate the importance of these enzymes in extra-oral and intra-tract digestion, and may explain the capability of the hemipteran to utilize diverse food sources.

Biochemical and toxicological properties of two acetylcholinesterases from the common bed bug, Cimex lectularius

We examined the molecular and enzymatic properties of two acetylcholinesterases (AChEs; ClAChE1 and ClAChE2) from the common bed bug, Cimex lectularius. Native polyacrylamide gel electrophoresis followed by activity staining and Western blotting revealed that ClAChE1 is the main catalytic enzyme and is abundantly expressed in various tissues. Both ClAChEs existed in dimeric form connected by a disulfide bridge and were attached to the membrane via a glycophosphatidylinositol anchor. To determine their kinetic and inhibitory properties, both ClAChE1 and ClAChE2 were in vitro expressed in Sf9 cells using a baculovirus expression system. ClAChE1 showed higher catalytic efficiency toward acetylcholine, supporting the hypothesis that ClAChE1 plays a major role in postsynaptic transmission. An inhibition assay revealed that ClAChE1 is generally more sensitive to organophosphates and carbamates examined although ClAChE2 was >4000-fold more sensitive to malaoxon than ClAChE1. The relatively higher correlation between the in vitro ClAChE1 inhibition and the in vivo toxicity suggested that ClAChE1 is the more relevant toxicological target for organophosphates and carbamates. Although the physiological function of ClAChE2 remains to be elucidated, ClAChE2 also appears to have neuronal functions, as judged by its tissue distribution and molecular and kinetic properties. Our findings help expand our knowledge on insect AChEs and their toxicological properties.

Comparative analysis of salivary gland transcriptomes of Phlebotomus orientalis sand flies from endemic and non-endemic foci of visceral leishmaniasis

Background

In East Africa, Phlebotomus orientalis serves as the main vector of Leishmania donovani, the causative agent of visceral leishmaniasis (VL). Phlebotomus orientalis is present at two distant localities in Ethiopia; Addis Zemen where VL is endemic and Melka Werer where transmission of VL does not occur. To find out whether the difference in epidemiology of VL is due to distant compositions of P. orientalis saliva we established colonies from Addis Zemen and Melka Werer, analyzed and compared the transcriptomes, proteomes and enzymatic activity of the salivary glands.

Methodology/Principal Findings

Two cDNA libraries were constructed from the female salivary glands of P. orientalis from Addis Zemen and Melka Werer. Clones of each P. orientalis library were randomly selected, sequenced and analyzed. In P. orientalis transcriptomes, we identified members of 13 main protein families. Phylogenetic analysis and multiple sequence alignments were performed to evaluate differences between the P. orientalis colonies and to show the relationship with other sand fly species from the subgenus Larroussius. To further compare both colonies, we investigated the humoral antigenicity and cross-reactivity of the salivary proteins and the activity of salivary apyrase and hyaluronidase.

Conclusions

This is the first report of the salivary components of P. orientalis, an important vector sand fly. Our study expanded the knowledge of salivary gland compounds of sand fly species in the subgenus Larroussius. Based on the phylogenetic analysis, we showed that P. orientalis is closely related to Phlebotomus tobbi and Phlebotomus perniciosus, whereas Phlebotomus ariasi is evolutionarily more distinct species. We also demonstrated that there is no significant difference between the transcriptomes, proteomes or enzymatic properties of the salivary components of Addis Zemen (endemic area) and Melka Werer (non-endemic area) P. orientalis colonies. Thus, the different epidemiology of VL in these Ethiopian foci cannot be attributed to the salivary gland composition.

Phlebotomus orientalis is the vector of visceral leishmaniasis (VL) caused by Leishmania donovani in Northeast Africa. Immunization with sand fly saliva or with individual salivary proteins has been shown to protect against leishmaniasis in different hosts, warranting the intensive study of salivary proteins of sand fly vectors. In our study, we characterize the salivary compounds of P. orientalis, thereby broadening the repertoire of salivary proteins of sand fly species belonging to the subgenus Larroussius. In order to find out whether there is any connection between the composition of P. orientalis saliva and the epidemiology of VL in two distinct Ethiopian foci, Addis Zemen and Melka Werer, we studied the transcriptomes, proteomes, enzymatic activities, and the main salivary antigens in two P. orientalis colonies originating from these areas. We did not detect any significant difference between the saliva of female sand flies originating in Addis Zemen (endemic area) and Melka Werer (non-endemic area). Therefore, the different epidemiology of VL in these Ethiopian foci cannot be related to the distant salivary gland protein composition. Identifying the sand fly salivary gland compounds will be useful for future research focused on characterizing suitable salivary proteins as potential anti-Leishmania vaccine candidates.

Lundep, a sand fly salivary endonuclease increases Leishmania parasite survival in neutrophils and inhibits XIIa contact activation in human plasma

Neutrophils are the host's first line of defense against infections, and their extracellular traps (NET) were recently shown to kill Leishmania parasites. Here we report a NET-destroying molecule (Lundep) from the salivary glands of Lutzomyia longipalpis. Previous analysis of the sialotranscriptome of Lu. longipalpis showed the potential presence of an endonuclease. Indeed, not only was the cloned cDNA (Lundep) shown to encode a highly active ss- and dsDNAse, but also the same activity was demonstrated to be secreted by salivary glands of female Lu. longipalpis. Lundep hydrolyzes both ss- and dsDNA with little sequence specificity with a calculated DNase activity of 300000 Kunitz units per mg of protein. Disruption of PMA (phorbol 12 myristate 13 acetate)- or parasite-induced NETs by treatment with recombinant Lundep or salivary gland homogenates increases parasite survival in neutrophils. Furthermore, co-injection of recombinant Lundep with metacyclic promastigotes significantly exacerbates Leishmania infection in mice when compared with PBS alone or inactive (mutagenized) Lundep. We hypothesize that Lundep helps the parasite to establish an infection by allowing it to escape from the leishmanicidal activity of NETs early after inoculation. Lundep may also assist blood meal intake by lowering the local viscosity caused by the release of host DNA and as an anticoagulant by inhibiting the intrinsic pathway of coagulation.

Salivary components from disease vectors help the arthropod to acquire blood. Here we show that an arthropod vector salivary enzyme affects the innate immune system of the host—mainly the destruction of neutrophil traps—allowing the Leishmania parasite to evade the host immune response and to cause an infection. This work highlights the relevance of vector salivary components in parasite transmission and further suggests the inclusion of these proteins as components for an anti-Leishmania vaccine. Importantly, because salivary proteins are always present at the site of natural transmission, this work further encourages the testing of vaccine candidates using the natural route of transmission—the bites of an arthropod vector—instead of current practices based solely on needle injection of parasites.

Role of adipokinetic hormone in stimulation of salivary gland activities: the fire bug Pyrrhocoris apterus L. (Heteroptera) as a model species

The effect of adipokinetic hormone (Pyrap-AKH) in stimulating the function of insect salivary glands (SGs) in extra-oral digestive processes was studied in the firebug, Pyrrhocoris apterus L. (Heteroptera). The analyses were performed on samples of SGs and extracts of linden seeds, a natural source of the bug's food. The SGs from 3-day old P. apterus females (when the food ingestion culminates), primarily contained polygalacturonase (PG) enzyme activity, whereas the level of lipase, peptidase, amylase and α-glucosidase was negligible. The transcription of PG mRNA and enzymatic activity were significantly increased in SGs after Pyrap-AKH treatment. The piercing and sucking of linden seeds by the bugs stimulated the intrinsic enzymatic cocktail of seeds (lipase, peptidase, amylase, glucosidase), and moreover the activity of these enzymes was significantly enhanced when the seeds were fed on by the Pyrap-AKH treated bugs. Similarly, a significant increase in PG activity was recorded in linden seeds fed on by hormonally-treated bugs or when injected by SG extract from hormonally treated ones as compared to untreated controls. The mechanism of AKH action in SGs is unknown, but likely involves cAMP (and excludes cGMP) as a second messenger, since the content of this compound doubled in SGs after Pyrap-AKH treatment. This new and as yet undescribed function of AKH in SGs is compared with the effect of this hormone on digestive processes in the midgut elucidated earlier.

Molecular characterization of tick salivary gland glutaminyl cyclase

Glutaminyl cyclase (QC) catalyzes the cyclization of N-terminal glutamine residues into pyroglutamate. This post-translational modification extends the half-life of peptides and, in some cases, is essential in binding to their cognate receptor. Due to its potential role in the post-translational modification of tick neuropeptides, we report the molecular, biochemical and physiological characterization of salivary gland QC during the prolonged blood feeding of the black-legged tick (Ixodes scapularis) and the gulf-coast tick (Amblyomma maculatum). QC sequences from I. scapularis and A. maculatum showed a high degree of amino acid identity to each other and other arthropods and residues critical for zinc binding/catalysis (D159, E202, and H330) or intermediate stabilization (E201, W207, D248, D305, F325, and W329) are conserved. Analysis of QC transcriptional gene expression kinetics depicts an upregulation during the bloodmeal of adult female ticks prior to fast-feeding phases in both I. scapularis and A. maculatum suggesting a functional link with bloodmeal uptake. QC enzymatic activity was detected in saliva and extracts of tick salivary glands and midguts. Recombinant QC was shown to be catalytically active. Furthermore, knockdown of QC transcript by RNA interference resulted in lower enzymatic activity, and small, unviable egg masses in both studied tick species as well as lower engorged tick weights for I. scapularis. These results suggest that the post-translational modification of neurotransmitters and other bioactive peptides by QC is critical to oviposition and potentially other physiological processes. Moreover, these data suggest that tick-specific QC-modified neurotransmitters/hormones or other relevant parts of this system could potentially be used as novel physiological targets for tick control.

[Tissue localization and expression difference of endogenous beta-glucosidase in digestive system of Musca domestica third instar larvae]

OBJECTIVE

To study the tissue localization and expression difference of endogenous beta-glucosidase in digestive system of Musca domestica third instar larvae.

METHODS

The digestive system of the 3rd instar larvae of Musca domestic was taken for the below tests. Tissue localization of endogenous beta-glucosidase mRNA was identified by in situ hybridization. Cellulase was localized by immunohistochemistry. The enzymatic activity of beta-glucosidase was measured by 3, 5-dinitrosalicylic acid(DNS) assay. The relative mRNA expression levels of M. domestica beta-glucosidase gene in these organs were determined by RT-PCR.

RESULTS

Beta-glucosidase mRNA, with in situ hybridization, was shown in the epithelial cells of midgut, salivary glands and foregut of the larvae. The immunohistochemical analysis on larvae tissues revealed that cellulase was produced and secreted by the epithelial cells of the midgut, salivary glands and foregut. beta-glucosidase activity in salivary glands, foregut, midgut, and hindgut was (0.80 +/- 0.06), (0.38 +/- 0.02), (1.20 +/- 0.05) and (0.26 +/- 0.02) IU/mg, respectively. There was significant difference in beta-glucosidase activity among these digestive organs (P < 0.05). The activity level of beta-glucosidase was highest in midgut [(45.45 +/- 1.27)%], and lowest in hindgut [(9.85 +/- 0.88)%]. However, beta-glucosidase gene were only expressed in the salivary gland, foregut and midgut. Significant differences in gene expression level of beta-glucosidase was found among these organs (P < 0.05). The relative expression quantity of beta-glucosidase gene in midgut and salivary glands were 5 and 3 times higher than that in foregut.

CONCLUSION

The endogenous beta-glucosidase gene is expressed in the foregut, midgut and salivary glands. The midgut and salivary glands of Musca domestica 3rd instar larvae are the primary organs of this enzyme secretion.

Endosymbiotic and host proteases in the digestive tract of the invasive snail Pomacea canaliculata: diversity, origin and characterization

Digestive proteases of the digestive tract of the apple snail Pomacea canaliculata were studied. Luminal protease activity was found in the crop, the style sac and the coiled gut and was significantly higher in the coiled gut. Several protease bands and their apparent molecular weights were identified in both tissue extracts and luminal contents by gel zymography: (1) a 125 kDa protease in salivary gland extracts and in the crop content; (2) a 30 kDa protease throughout all studied luminal contents and in extracts of the midgut gland and of the endosymbionts isolated from this gland; (3) two proteases of 145 and 198 kDa in the coiled gut content. All these proteases were inhibited by aprotinin, a serine-protease inhibitor, and showed maximum activity between 30°C and 35°C and pH between 8.5 and 9.5. Tissue L-alanine-N-aminopeptidase activity was determined in the wall of the crop, the style sac and the coiled gut and was significantly higher in the coiled gut. Our findings show that protein digestion in P. canaliculata is carried out through a battery of diverse proteases originated from the salivary glands and the endosymbionts lodged in the midgut gland and by proteases of uncertain origin that occur in the coiled gut lumen.

Rac1 GTPase acts downstream of αPS1βPS integrin to control collective migration and lumen size in the Drosophila salivary gland

During collective migration of the Drosophila embryonic salivary gland, the distal gland cells mediate integrin-based contacts with surrounding tissues while proximal gland cells change shape and rearrange. Here, we show that αPS1βPS integrin controls salivary gland migration through Rac1 GTPase which downregulates E-cadherin in proximal and distal gland cells, and promotes extension of actin-rich basal membrane protrusions in the distal cells. In embryos mutant for multiple edematous wings (mew), which encodes the αPS1 subunit of the αPS1βPS integrin heterodimer, or rac1 and rac2 GTPases, salivary gland cells failed to migrate, to downregulate E-cadherin and to extend basal membrane protrusions. Selective inhibition of Rac1 in just the proximal or distal gland cells demonstrate that proximal gland cells play an active role in the collective migration of the whole gland and that continued migration of the distal cells depends on the proximal cells. Loss of rac1rac2 also affected gland lumen length and width whereas, loss of mew affected lumen length only. Activation of rac1 in mew mutant embryos significantly rescued the gland migration, lumen length and basal membrane protrusion defects and partially rescued the E-cadherin defects. Independent of mew, Rac regulates cell shape change and rearrangement in the proximal gland, which is important for migration and lumen width. Our studies shed novel insight into a Rac1-mediated link between integrin and cadherin adhesion proteins in vivo, control of lumen length and width and how activities of proximal and distal gland cells are coordinated to result in the collective migration of the entire salivary gland.

Proteomic profiling of cereal aphid saliva reveals both ubiquitous and adaptive secreted proteins

The secreted salivary proteins from two cereal aphid species, Sitobion avenae and Metopolophium dirhodum, were collected from artificial diets and analysed by tandem mass spectrometry. Protein identification was performed by searching MS data against the official protein set from the current pea aphid (Acyrthosiphon pisum) genome assembly and revealed 12 and 7 proteins in the saliva of S. avenae and M. dirhodum, respectively. When combined with a comparable dataset from A. pisum, only three individual proteins were common to all the aphid species; two paralogues of the GMC oxidoreductase family (glucose dehydrogenase; GLD) and ACYPI009881, an aphid specific protein previously identified as a putative component of the salivary sheath. Antibodies were designed from translated protein sequences obtained from partial cDNA sequences for ACYPI009881 and both saliva associated GLDs. The antibodies detected all parent proteins in secreted saliva from the three aphid species, but could only detect ACYPI009881, and not saliva associated GLDs, in protein extractions from the salivary glands. This result was confirmed by immunohistochemistry using whole and sectioned salivary glands, and in addition, localised ACYPI009881 to specific cell types within the principal salivary gland. The implications of these findings for the origin of salivary components and the putative role of the proteins identified are discussed in the context of our limited understanding of the functional relationship between aphid saliva and the plants they feed on. The mass spectrometry data have been deposited to the ProteomeXchange and can be accessed under the identifier PXD000113.

Identification and characterization of sialidase-like activity in the developmental stages of Amblyomma variegatum

Amblyomma variegatum F. are obligate hematophagous ectoparasites of livestock that serve as the vectors of Ehrlichia ruminantium (formerly known as Cowdria ruminantium), the causative agent of heartwater disease. In the light of the fact that they are blood-feeding, their salivary glands play prominent role in their acquisition of nutrients from the bloodmeal. Sialic acids are a major component of glycoprotein in mammalian blood fluid and cells. Sialome of hard ticks is still sparse. Here, for the first time, the possible expression of sialidase in A. variegatum was investigated. Our finding established the presence of type II sialidase-like activity in the three stages (larva, nymph, and adult) of the fed and unfed tick. There was no statistically significant difference in sialidase activity in the various stages of this ectoparasite (P > 0.05). The enzyme was purified by combination of salting out and ion exchange chromatography on DEAE--cellulose and hydroxylapatite columns. Characterization of the enzyme revealed that it is optimally active at 40 degrees C and pH 5.5, and is activated by bivalent cations Zn2+ or Fe2+. The enzyme has a Km of 0.023 mM and Vmax of 0.16 millimol/min with Fetuin as the substrate. To assess the susceptibility of some mammalian cells to the tick sialidase, we prepared erythrocyte ghost cells from different animals, which were incubated with the enzyme. Results revealed that the ruminant cells were better substrates. Our work and findings contribute to the preliminary characterization of the A. variegatum salivary proteome, and may pave way to the development of new acaricides.

Molecular cloning and characterization of an endogenous digestive β-glucosidase from the midgut of the fungus-growing termite Macrotermes barneyi

β-glucosidase from the midgut of the fungus-growing termite Macrotermes barneyi was first cloned and characterized to gain a better understanding of cellulolytic systems in fungus-growing termites. β-glucosidase activity was proven to present primarily in the midgut of M. barneyi and two β-glucosidases were partially purified from the midgut. Based on the N-terminus sequence of one of the β-glucosidases, a full-length cDNA fragment of 1708 bp was obtained. This sequence encodes a 493 amino acid protein belonging to glycoside hydrolase family 1. Quantitative real-time PCR analysis proved that the β-glucosidase gene was primarily expressed in the midgut. β-glucosidase was expressed heterologously and biochemically characterized. Results indicate that β-glucosidase is an endogenous, midgut-origin termite digestive enzyme. It may have applications in understanding the mechanism of lignocellulose degradation in fungus-growing termites.

Prey digestion in the midgut of the predatory bug Podisus nigrispinus (Hemiptera: Pentatomidae)

Pre-oral digestion is described as the liquefaction of the solid tissues of the prey by secretions of the predator. It is uncertain if pre-oral digestion means pre-oral dispersion of food or true digestion in the sense of the stepwise bond breaking of food polymers to release monomers to be absorbed. Collagenase is the only salivary proteinase, which activity is significant (10%) in relation to Podisus nigrispinus midgut activities. This suggests that pre-oral digestion in P. nigrispinus consists in prey tissue dispersion. This was confirmed by the finding of prey muscles fibers inside P. nigrispinus midguts. Soluble midgut hydrolases from P. nigrispinus were partially purified by ion-exchange chromatography, followed by gel filtration. Two cathepsin L-like proteinases (CAL1 and CAL2) were isolated with the properties: CAL1 (14.7 kDa, pH optimum (pHo) 5.5, km with carbobenzoxy-Phe-Arg-methylcoumarin, Z-FR-MCA, 32 μM); CAL2 (17 kDa, pHo 5.5, km 11 μM Z-FR-MCA). Only a single molecular species was found for the other enzymes with the following properties are: amylase (43 kDa, pHo 5.5, km 0.1% starch), aminopeptidase (125 kDa, pHo 5.5, km 0.11 mM l-Leucine-p-nitroanilide), α-glucosidase (90 kDa, pHo 5.0, km 5mM with p-nitrophenyl α-d-glucoside). CAL molecular masses are probably underestimated due to interaction with the column. Taking into account the distribution of hydrolases along P. nigrispinus midguts, carbohydrate digestion takes place mainly at the anterior midgut, whereas protein digestion occurs mostly in middle and posterior midgut, as previously described in seed- sucker and blood-feeder hemipterans.

[Lysozyme activity of the salivary gland secretion of the medicinal leech H. verbana, H. medicinalis and H. orientalis]

Salivary gland secretions of three species of the medicinal leech differ in the level of lysozyme peptidoglycan-lysing activity. Using the synthetic fluorogenic substrate, 4-methyl-umbelliferyl tetra N-acetyl-beta-chitotetraosid, the glycosidase activity (as one of peptidoglycan-lysing activities) of salivary gland secretion of three species of the medicinal leech was quantitatively evaluated in comparison with egg lysozyme. It is supposed, that lysozyme activity of the leech secretions is determined not only by 5 isoforms of destabilase-lysozyme, but by some other enzymes which can utilize this substrate. These may be lysozymes other than i- (invertebrate) lysozymes (such as destabilase-lysozyme, or related enzymes).

Identification and characterization of three cholinesterases from the common bed bug, Cimex lectularius

We identified and characterized the full-length cDNA sequences encoding two acetylcholinesterases (ClAChE1 and ClAChE2) and a salivary gland-specific cholinesterase-like protein (ClSChE) from the common bed bug, Cimex lectularius. All three cholinesterase genes (Clac1, Clace2 and Clsce) have conserved motifs, including a catalytic triad, a choline-binding site and an acyl pocket. Phylogenetic analysis showed that ClAChE1 belongs to the insect AChE1 clade, whereas ClAChE2 belongs to the insect AChE2 clade. ClSChE was grouped into the clade containing all AChE1s, suggesting a paralogous relationship to ClAChE1. Transcription levels of Clace1 were higher than those of Clace2 in all tissues examined, including the central nervous system (CNS). In contrast, the Clsce transcript was not detected in the CNS but specifically found in the salivary gland at much higher levels (>3000-fold) than those of Clace1 and Clace2. Western blot analysis using anti-ClAChE antibodies, in conjunction with activity staining, revealed that ClAChE1 is more active than ClAChE2, whereas ClSChE has little enzyme activity. Three-dimensional structure modelling suggested that ClAChEs and ClSChE shared structural similarities, but had some differences in the residues forming the acyl pocket and oxyanion hole. The current findings should provide valuable insights into the evolution and functional diversification of insect cholinesterase.

The blowfly salivary gland - a model system for analyzing the regulation of plasma membrane V-ATPase

Vacuolar H(+)-ATPases (V-ATPases) are heteromultimeric proteins that use the energy of ATP hydrolysis for the electrogenic transport of protons across membranes. They are common to all eukaryotic cells and are located in the plasma membrane or in membranes of acid organelles. In many insect epithelia, V-ATPase molecules reside in large numbers in the apical plasma membrane and create an electrochemical proton gradient that is used for the acidification or alkalinization of the extracellular space, the secretion or reabsorption of ions and fluids, the import of nutrients, and diverse other cellular activities. Here, we summarize our results on the functions and regulation of V-ATPase in the tubular salivary gland of the blowfly Calliphora vicina. In this gland, V-ATPase activity energizes the secretion of a KCl-rich saliva in response to the neurohormone serotonin (5-HT). Because of particular morphological and physiological features, the blowfly salivary glands are a superior and exemplary system for the analysis of the intracellular signaling pathways and mechanisms that modulate V-ATPase activity and solute transport in an insect epithelium.

Characterization of glucose-induced glucose oxidase gene and protein expression in Helicoverpa armigera larvae

Caterpillar labial salivary enzyme glucose oxidase (GOX) plays an important role in plant-insect interactions by suppressing the caterpillar-induced nicotine production in tobacco plants. In the present study, we cloned and characterized the GOX gene (HaGox) from labial salivary glands of Helicoverpa armigera larvae using 3' and 5' RACE, homologous analysis, phylogenetic analysis, LC-MS/MS, and qRT-PCR. The deduced GOX amino acid sequence (606 amino acids) shares 99% and 76% identity with H. zea and Spodoptera exigua GOX, respectively, and is consistent with the GOX protein sequence identified from H. armigera labial salivary gland. These results confirmed that the HaGox encode the GOX protein. Transcript levels of HaGox in larval labial salivary glands were significantly higher than those in midgut and hemolymph, respectively, and those of caterpillars reared on tobacco leaves coated with 0.1%, 1%, and 10% glucose solutions were significantly higher than those reared on 0.01% glucose-coated leaves or control tobacco leaves. Western blot and native PAGE showed that GOX protein expression levels and GOX enzymatic activities also increased with dietary glucose. These results proved that GOX expressions in larval labial salivary glands induced by dietary glucose were exhibited not only on transcriptional levels, but also on translational/posttranslational levels.

Role of proteases in extra-oral digestion of a predatory bug, Andrallus spinidens

Roles of salivary proteases in the extra-oral digestion of the predatory bug, Andrallus spinidens Fabricius (Hemiptera: Pentatomidae) were studied by using 2% azocasein as a general substrate and specific protease substrates, as well as synthetic and endogenous inhibitors. It was found that salivary glands of A. spinidens have two anterior, two lateral, and two posterior lobes. Azocasein was used to measure the activity of general proteases in the salivary glands using different buffer solutions. The enzyme had the highest activity at pH 8. General protease activity was highest at 40 °C and was stable for 6-16 hours. The use of specific substrates showed that trypsin-like, chymotrypsin-like, aminopeptidase, and carboxypeptidase are the active proteases present in salivary glands, by the maximum activity of trypsin-like protease in addition to their optimal pH between 8-9. Ca(2+) and Mg(2+) increased proteolytic activity about 216%, while other ions decreased it. Specific inhibitors including SBTI, PMSF, TLCK, and TPCK significantly decreased enzyme activity, as well as the specific inhibitors of methalloproteases including phenanthroline, EGTA, and TTHA. Extracted endogenous trypsin inhibitors extracted from potential prey, Chilo suppressalis, Naranga aenescens, Pieris brassicae, Hyphantria cunea, and Ephestia kuhniella, had different effects on trypsin-like protease activity of A. spinidens salivary glands. With the exception of C. suppressalis, the endogenous inhibitors significantly decreased enzyme activity in A. spinidens.

The activity of platelet activating factor-acetyl hydrolase (PAF-AH) in the salivary glands of Rhodnius prolixus

In this work, we investigated the activity of the platelet activating factor acetyl hydrolase (PAF-AH) in the salivary gland homogenates and saliva of Rhodnius prolixus. PAF-AH activity in the salivary gland homogenates was lower than in the saliva. Preliminary characterization of the enzyme demonstrated that it hydrolyzed the substrate 2-thio-PAF, was detectable just in 1 pair of salivary gland homogenates in 0.5 ml buffer, and was stable under different conditions. PMSF, TPCK, TLCK, pepstatin A and p-BPB all inhibited the PAF-AH activity. Enzyme specific activity in salivary gland homogenates diminished immediately after feeding of 5th-instar larvae, and increased before feeding by adult insects. 2-Thio-PAF induced platelet-aggregation that was inhibited by previous incubation of the substrate with salivary gland homogenates or saliva. The relevance of PAF-AH for providing Rhodnius with a feeding mechanism for facilitating the sucking of a high volume of blood meal in a short period is discussed.

Influence of the intestinal anticoagulant in the feeding performance of triatomine bugs (Hemiptera; Reduviidae)

Triatomines are haematophagous insects in all post-embryonic life stages. They are vectors of Trypanosoma cruzi, the causative agent of Chagas disease. Their vectorial ability is influenced by their feeding performance, which varies greatly amongst species. Recent work showed that inhibition of the coagulation process in the anterior midgut (crop) environment considerably influences the blood meal size. In this work, we performed a comparative study of the level of anticoagulant activity in the saliva and crop contents of three triatomine species -Triatoma infestans, Triatoma brasiliensis and Rhodnius prolixus - and correlated this with their feeding performance on live hosts. Moreover, the feeding parameters on a large diameter vessel influenced by the crop anticoagulants were evaluated in detail. The anticoagulant activity was significantly higher in the crop contents than in salivary glands, varying from 1.6-fold higher for R. prolixus to 70-fold higher for T. brasiliensis. Amongst the species, T. brasiliensis had the lowest crop anticoagulant activity, the lowest concentration of thrombin inhibitor, and took the longest to feed. Triatoma brasiliensis nymphs that had their intestinal anticoagulant (brasiliensin) knocked down by RNA interference had the lowest capacity to maintain cibarial pump frequency at higher levels throughout the feeding process and consequently a lower ingestion rate (mg/min), even when fed under favourable conditions (large diameter vessel). However, the feeding difficulty for brasiliensin knockdown T. brasiliensis nymphs was reversed by treating the host mice with heparin (a potent systemic anticoagulant) before blood feeding. The results indicate that crop anticoagulant activity influences modulation of the blood-pumping frequency to the intestine and significantly affects the feeding efficiency of triatomine spp. on live hosts.

[Expression of p38MAPK in salivary adenoid cystic carcinoma and their significance]

OBJECTIVE

To investigate the expression of p38 mitogen-activated protein kinase (p38MAPK) in salivary adenoid cystic carcinoma (SACC) tissues and their clinicopathologic significance.

METHODS

The protein and mRNA expressions of p38MAPK were examined by immunohistochemistry and in situ hybridization, respectively, in 52 cases of SACC and in 11 normal salivary gland tissues adjacent to the tumors on a tissue microarray platform.

RESULTS

The positive rate of p38MAPK protein expression in the paracancerous normal salivary gland tissues and that in SACC were 36.4% and 96.2%, respectively, showing a significant statistical difference (P < 0.01). The protein expression of p38MAPK was positively correlated with the lymph node metastasis and nerve involvement (P < 0.05). The positive rates of p38MAPK mRNA in the paracancerous tissues and in the SACC tissues were 45.5% and 94.2%, respectively, with a significant statistical difference (P < 0.01). The mRNA expression of p38MAPK was positively correlated with the lymph node metastasis and nerve involvement (P < 0.05). In the SACC, there was a notable positive correlation between the p38MAPK protein and mRNA expressions (r = 0.409, P < 0.01).

CONCLUSIONS

The expression of p38MAPK is up-regulated in salivary adenoid cystic carcinoma. p38MARK may be involved in the tumorigenesis, development and metastasis of this cancer.

Characterization of a glutenin-specific serine proteinase of Sunn bug Eurygaster integricepts Put

Glutenin hydrolyzing proteinases (GHPs) have been purified, by affinity chromatography, from wheat seeds damaged by the Sunn bug Eurygaster integriceps (Hemiptera, Scutelleridae). A 28 kDa protein was partially sequenced by mass spectrometry and Edman degradation which showed homology to serine proteases from various insects. Three full length clones were obtained from cDNA isolated from Sunn bug salivary glands using degenerate PCR based on the sequences obtained. The cleavage site of the protease was determined using recombinant and synthetic peptides and shown to be between the consensus hexapeptide and nonapeptide repeat motifs present in the high molecular weight subunits of wheat glutenin (PGQGQQ∧GYYPTSLQQ). Homology models were generated for the three proteinases identified in this study using the high resolution X-ray structure of a crayfish (Pontastacus leptodactylus) trypsin complexed with a peptide inhibitor as template (PDB accession 2F91). The novel specificity of this protease may find applications in both fundamental and applied studies.

[Changes of NO-ergic activity in the salivary glands of rats under conditions of omeprazole-induced hypergastrinemia]

Under conditions of omeprazole-induced hypergastrinemia the activity of NOS and the concentration of NO2-, the end product of metabolism of nitric oxide were studied in salivary glands of rats. We detected an increase in NOS activity, reaching a maximum (7.61+/-0.39 Mmol [NO2-]/(g*min) at 14th day of the experiment. At 28th day following omeprazole introduction its activity was 5,76+/-0.25 Mmol [NO2-]/(g*min).

Functional and translational analyses of a beta-glucosidase gene (glycosyl hydrolase family 1) isolated from the gut of the lower termite Reticulitermes flavipes

This research focused on digestive beta-glucosidases from glycosyl hydrolase family (GHF) 1 from the gut of the lower termite Reticulitermes flavipes. In preceding studies on R. flavipes, we characterized beta-glucosidase activity across the gut and its inhibition by carbohydrate-based inhibitors, and subsequently we identified two partial beta-glucosidase cDNA sequences from a host gut cDNA library. Here, we report on the full-length cDNA sequence for one of the R. flavipes beta-glucosidases (RfBGluc-1), the expression of its mRNA in the salivary gland and foregut, the production of recombinant protein using a baculovirus-insect expression system, optimal recombinant substrate specificity profiles and parameters, and significant inhibition by the established beta-glucosidase inhibitor cellobioimidazole. We also report the partial cDNA sequence for a second gut beta-glucosidase (RfBGluc-2), and show that like RfBGluc-1 its mRNA is localized mainly in the salivary gland. Other results for RfBGluc-1 showing activity against laminaribose, a component of microbial cell walls, suggest that RfBGluc-1 may serve dual functions in cellulose digestion and immunity. These findings provide important information that will enable the testing of hypotheses related to collaborative host-symbiont lignocellulose digestion, and that contributes to the development of next-generation termiticides and novel biocatalyst cocktails for use in biomass-to-bioethanol applications.

A salivary serine protease of the haematophagous reduviid Panstrongylus megistus: sequence characterization, expression pattern and characterization of proteolytic activity

A cDNA encoding a trypsin-like protease from the salivary glands of the haematophagous reduviid Panstrongylus megistus was cloned and sequenced. The deduced protein sequence showed similarities to serine proteases of other hemipterans but with substitutions in the catalytic triad and the substrate binding site. The expression of the gene increased more than sixfold after feeding. Saliva showed the highest proteolytic activity at neutral to slightly basic pH. Substrate and inhibitor profiles and zymography indicated the presence of a trypsin-like protease with preference for Arg and Lys at P1. Using chromatography, a fibrinolytic enzyme was purified whose sequence was identified by tandem mass spectrometry as that encoded by the cDNA.

Expression of neuron-specific enolase in irradiated salivary glands of the rat: a pilot study

External irradiation of advanced head and neck cancer often includes the major salivary glands, despite them not being affected by the disease. The aim of this study was to determine neuron-specific enolase (NSE) as a marker of inflammation in irradiated and non-irradiated salivary glands of the rat. This study shows that NSE expression in irradiated salivary glands is dependent on the topography of the organ related to the irradiation source. NSE immunostaining was increased in irradiated rats, both in glands directly exposed to the irradiation source and in shielded glands, and compared to glands of non-irradiated animals. Staining of NSE in salivary glands appears to indicate the inflammatory response of the organ to X-ray exposure. The increased immunoreactivity for NSE in shielded glands might be useful as a marker of irradiation in salivary glands, even for scattered radiation effects in major salivary glands.

Molecular characterization and expression of laccase genes in the salivary glands of the green rice leafhopper, Nephotettix cincticeps (Hemiptera: Cicadellidae)

The green rice leafhopper, Nephotettix cincticeps has a laccase (EC 1.10.3.2) in its salivary glands and saliva, possibly playing an important role in detoxifying plant phenolics and in salivary sheath coagulation during feeding. We aimed to clarify the function of saliva-specific laccase in a vascular-feeding insect, N. cincticeps, for which we cloned 2 cDNAs (NcLac1S and NcLac1G) from the salivary glands and 1 cDNA (NcLac2) from the epidermis. The NcLac1S, NcLac1G, and NcLac2 transcripts encoded 701-, 792-, and 729-amino-acid proteins, respectively. The putative proteins encoded by NcLac1S and NcLac2 were predicted to be soluble, whereas that encoded by NcLac1G was hydrophobic and predicted to have a C-terminal transmembrane domain. Real-time reverse transcriptase polymerase chain reaction analysis revealed that NcLac1S was expressed exclusively, and at a much higher level than NcLac1G and NcLac2 in the salivary glands. NcLac1G was also expressed in the epidermis, midgut, and Malpighian tubules. NcLac2 expression was highest in the epidermis. In situ hybridization revealed NcLac1S expression in the V-cells of the salivary glands, having proven laccase activity. Expression of NcLac1G and NcLac2 were not detected clearly in all cells in the salivary glands. Therefore, NcLac1S is responsible for the laccase activity detected in the salivary glands and saliva of this insect. This is the first report on gene cloning of salivary laccase from a vascular-feeding insect.

Equine mandibular gland: in situ characterisation of sialoderivatives

REASONS FOR PERFORMING STUDY

Sialic acids modulate the metabolite transport across membranes and may be involved in protection against pathogenic agents. The presence of sialoderivatives in the equine mandibular gland requires further study.

OBJECTIVE

To biochemically visualise in situ the presence of sialoderivatives, by means of mild and strong periodate oxidation and alcoholic saponification, combined with lectin histochemistry and sialidase digestion in order to hypothesise roles for detached sialoderivatives.

METHODS

Mandibular glands were removed from 8 mature horses of both sexes and subjected to histochemical procedures, including periodate oxidation, saponfication and lectin staining. Controls were based upon the omission of peroxidase-conjugated lectins and respective enzyme-free buffers.

RESULTS

The reactivities of PNA and RCA I lectins were affected by sialidase treatment, whether preceded by saponification or not, showing that the dimer N-acetyl-sialic acid-beta-Gal was linked (1-3)GalNAc and (1-4)GlcNAc. In acinar cells the sequence sialic acid-beta-Gal(1-3)GalNAc showed sialic residues acetylated at C4 only and at C4 and C7 and/or C8 and/or C9(alpha2-6Gal) in both sexes, while in female mandibular gland also C4 and C9(alpha2-3Gal) acetylated residues were present. Sialic acid linked to beta-Gal(1-4)GlcNAc was prevalently C4 and C7 and/or C8 and/or C9(alpha2-6Gal and alpha2-3Gal) acetylated, whereas only a minor quantity showed acetyl groups at C7 and/or C8 and/or C9(alpha2-6Gal) in the acinar cells of both sexes.

CONCLUSIONS

The great variety of sialic acid residues expressed by equine mandibular gland could assume an important role in the defensive mechanisms towards pathogen agents and, compared with those of cattle, probably represents an example of molecular species-specificity related to different alimentary habits.

Expression and RNA interference of salivary polygalacturonase genes in the tarnished plant bug, Lygus lineolaris

Three genes encoding polygalacturonase (PG) have been identified in Lygus lineolaris (Palisot de Beauvois) (Miridae: Hemiptera). Earlier studies showed that the three PG gene transcripts are exclusively expressed in the feeding stages of L. lineolaris. In this report, it is shown that all three transcripts are specifically expressed in salivary glands indicating that PGs are salivary enzymes. Transcriptional profiles of the three PGs were evaluated with respect to diet, comparing live cotton plant material to artificial diet. PG2 transcript levels were consistently lower in cotton-fed insects than those reared on artificial diet. RNA interference was used to knock down expression of PG1 mRNA in adult salivary glands providing the first demonstration of the use of this method in the non-model insect, L. lineolaris.

Functional characterization of a salivary apyrase from the sand fly, Phlebotomus duboscqi, a vector of Leishmania major

Two transcripts coding for proteins homologous to apyrases were identified by massive sequencing of a Phlebotomus (P.) duboscqi salivary gland cDNA library. The sequence analysis revealed that the amino acids important for enzymatic activity including nucleotidase activity and the binding of calcium and nucleotides were well conserved in these molecules. A recombinant P. duboscqi salivary apyrase was expressed in Escherichia coli and purified. The resulting protein efficiently hydrolyzed ADP and ATP, but not AMP, GDP, CDP or UDP, in a calcium-dependent manner. Further, the recombinant protein inhibited ADP- and collagen-induced platelet aggregation. The results indicated that this salivary protein plays an important role in the blood-feeding process in P. duboscqi. Its unique enzymatic activity makes the salivary apyrase an attractive candidate as a therapeutic agent for the treatment of thrombotic pathologies as well as a reagent for a wide variety of research purposes.

The effects of different prey regimes on the proteolytic digestion of nymphs of the spined soldier bug, Podisus maculiventris (Hemiptera: Pentatomidae)

The effects of different prey regimes on the performance and digestive physiology of the spined soldier bug, Podisus maculiventris (Say) (Hemiptera: Pentatomidae), were assessed. Specifically, P. maculiventris nymphs were fed on Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), larvae; Egyptian cotton leafworm (ECW); Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae); larvae; Calliphora spp. (CAL) (Diptera: Calliphoridae) pupae or a mixture of the three prey. No differences in development and weight gain were observed when P. maculiventris nymphs were fed different prey species (CPB, ECW or CAL). However, an increase in weight gain and a reduction in the duration of the stadia were observed for nymphs fed with a mixture of the three prey. To investigate the physiological background, biochemical analysis were carried out on insects dissected at the end of the feeding assay. We have found that the proteolytic activity in the salivary glands of P. maculiventris nymphs was not affected by prey species, whereas the relative activity of these proteases in the midgut depends on the prey. Moreover, gel assays proved that the proteolytic profiles of midguts from P. maculiventris nymphs feeding on CPB, ECW and CPB closely resembled those of their prey. All together, these results suggest that P. maculiventris may utilize enzymes from the prey they consume that may facilitate the process of digestion.