Cathepsin L-a novel cysteine protease from Haemaphysalis flava Neumann, 1897

Functional annotation and analysis of the hard tick Dermacentor nuttalli midgut genes

Ticks are hematophagous vectors that transmit a variety of pathogens, posing significant threats to the health of both humans and animals. Tick midgut proteins play essential roles in blood digestion, feeding, toxic waste processing, and pathogen transmission. Dermacentor nuttalli is the primary vector of tick-borne pathogens, including rickettsioses in the Qinghai-Tibet Plateau. However, there is a lack of genomic, transcriptomic, and proteomic information regarding the biology of D. nuttalli. In this study, we assembled and compared the midgut transcriptomes of female D. nuttalli ticks at 0, 24, 48, 72, and 96 h during blood feeding, identifying the genes with differentially regulated expression following feeding. The obtained data were compiled and annotated in multiple databases including Nr, NT, PFAM, KOG, KEGG, and GO. The high-quality clean readings of midgut tissue at the different blood-feeding times were recorded as 22,524,912, 23,752,325, 20,377,718, 21,300,710, and 20,378,658, respectively. The transcripts were classified into eight large categories, including immunogenic proteases (8.37%), protease inhibitors (0.85%), transporters (3.96%), ligand binding proteins (1.98%), ribosomal function proteins (0.94%), heat shock proteins (0.30%), other proteases and miscellaneous proteins (57.61%), and unknown proteins (26.00%). Significant differences were observed in the genes obtained at 0, 24, 48, 72, and 96 h during blood feeding. The differentially expressed genes include catalytic proteins that play an important role in accelerating biochemical reactions, binding activity proteins which are involved in various molecular interactions, and proteins that actively participate in multiple metabolic pathways and cellular processes. Notably, the gene expression in the midgut of D. nuttalli shows dynamic changes every 24 h throughout the blood-feeding process. This change may represent an equivalent strategy of antigenic variation for ticks, designed to protect their essential feeding function against the host's immune system. The tick antigens identified in this study may serve as promising candidates for the development of effective vaccines or as drug targets for acaricides.

The diurnal salivary glands transcriptome of Dermacentor nuttalli from the first four days of blood feeding

The ixodid tick Dermacentor nuttalli is distributed from southern Siberia to North China and is a vector of many pathogens. This species can have severe impacts on animal husbandry and human health. To date, the control of D. nuttalli is limited to the use of acaricides such as organophosphorus, synthetic pyrethroids and amidine pesticides. There are no environmentally friendly or reliable prevention and control measures, and little is known regarding key antigens involved in blood feeding. Salivary glands are major tissues involved in the blood feeding and pathogen transmission of ticks. Therefore, this study focused on salivary glands tissue to identify the dominant antigens of D. nuttalli involved in tick feeding. For this, high-throughput RNA sequencing (RNA-seq) was used for analysis. The transcriptome of female D. nuttalli ticks was assembled and characterized, and differentially expressed genes (DEGs) were identified in the salivary glands of ticks that had not fed (0 h) and of ticks after 24, 48, 72 and 96 h of feeding. There were 22,802,784, 22,275,013, 26,629,453, 24,982,389, and 22,596,230 high-quality clean reads obtained from salivary glands tissues at the five different blood feeding time points. The total number of annotated unigenes was 100,347. The differences in gene expression between different time points were compared, and functional enrichment was performed. Quantitative reverse transcription PCR (RT‒qPCR) was used to validate the RNA-seq results, the results of which showed that the differences in expressed transcripts presented similar trends. Among the identified DEGs, the most numerous were those with catalytic and binding activities and those involved in diverse metabolic pathways and cellular processes. The expression patterns of homologous and family-member proteins throughout the blood feeding period exhibited significant differences, strongly suggesting that the transcriptome composition is highly dynamic and likely subjected to important variation throughout the life cycle. Studies of gene sequences in D. nuttalli will greatly increase the information on tick protective antigens, which could potentially function as effective vaccine candidates or drug targets for the development of environmentally friendly acaricides.

De novo assembled transcriptomics assisted label-free quantitative proteomics analysis reveals sex-specific proteins in the intestinal tissue of Haemaphysalis qinghaiensis

The hard tick Haemaphysalis qinghaiensis is the vector of a wide variety of infectious agents, such as spirochetes and other bacteria as well as viruses in the western plateau of China. Tick midgut is the key tissue involved in the host-pathogen-vector interface. Multiple midgut proteins are related to key functions in blood digestion, tick survival, and tick-borne pathogen transmission. However, information on the sex-specific proteins expressed in the midgut tissue of H. qinghaiensis for which the genome has not been sequenced is limited. Hence, we assembled and characterized the transcriptome of the H. qinghaiensis midgut and identified the differentially expressed genes (DEGs) in female and male ticks. The sequencing of the mRNA for this nonmodel species is essential for producing a protein database for mass spectrometry-based identification. Here, we combined high-throughput parallel sequencing and label-free quantitative proteomics analysis to extensively characterize the tick midgut using massive RNA sequencing and mass spectrometry, which allowed the detection of genes and proteins. A total of 279,186 transcripts were annotated into 125,790 coding sequences (CDSs), which were manually curated into 96 different gene families. A total of 12,837 DEGs between the two sexes were found by RNA-seq analysis. Of these, 5401 were upregulated genes, while 7436 were downregulated genes. The most common molecular functions were those related to the endocrine system, translation, signal transduction, transport, and catabolism. Meanwhile, the most common biological processes were related to cellular processes, metabolic processes, cellular anatomical entities, and cargo receptor activities. An analysis of the label-free protein quantitation dataset showed 272 upregulated proteins and 46 downregulated proteins when the fold-change was >2.0 (LC-MS/MS). Association analysis of the transcriptome and proteome with GO functional enrichment showed that the majority of the genes (proteins) were those related to catalytic activity, binding, cellular processes, metabolic processes, and responses to stimuli. This study aims to elucidate the digestive physiology of H. qinghaiensis as well as its physiological sexual dimorphism. This will allow the identification of protein candidates with physiological importance that could be used as targets to control the vector as well as the transmission of tick-borne pathogens to humans and animals.

A proteomics informed by transcriptomics insight into the proteome of Ornithodoros erraticus adult tick saliva

BACKGROUND

The argasid tick Ornithodoros erraticus is the main vector of tick-borne human relapsing fever (TBRF) and African swine fever (ASF) in the Mediterranean Basin. The prevention and control of these diseases would greatly benefit from the elimination of O. erraticus populations, and anti-tick vaccines are envisaged as an effective and sustainable alternative to chemical acaricide usage for tick control. Ornithodoros erraticus saliva contains bioactive proteins that play essential functions in tick feeding and host defence modulation, which may contribute to host infection by tick-borne pathogens. Hence, these proteins could be candidate antigen targets for the development of vaccines aimed at the control and prevention of O. erraticus infestations and the diseases this tick transmits. The objective of the present work was to obtain and characterise the proteome of the saliva of O. erraticus adult ticks as a means to identify and select novel salivary antigen targets.

METHODS

A proteomics informed by transcriptomics (PIT) approach was applied to analyse samples of female and male saliva separately using the previously obtained O. erraticus sialotranscriptome as a reference database and two different mass spectrometry techniques, namely liquid chromatography-tandem mass spectrometry (LC-MS/MS) in data-dependent acquisition mode and sequential window acquisition of all theoretical fragment ion spectra MS (SWATH-MS).

RESULTS

Up to 264 and 263 proteins were identified by LC-MS/MS in the saliva of O. erraticus female and male ticks, respectively, totalling 387 non-redundant proteins. Of these, 224 were further quantified by SWATH-MS in the saliva of both male and female ticks. Quantified proteins were classified into 23 functional categories and their abundance compared between sexes. Heme/iron-binding proteins, protease inhibitors, proteases, lipocalins and immune-related proteins were the categories most abundantly expressed in females, while glycolytic enzymes, protease inhibitors and lipocalins were the most abundantly expressed in males. Ninety-seven proteins were differentially expressed between the sexes, of which 37 and 60 were overexpressed in females and males, respectively.

CONCLUSIONS

The PIT approach demonstrated its usefulness for proteomics studies of O. erraticus, a non-model organism without genomic sequences available, allowing the publication of the first comprehensive proteome of the saliva of O. erraticus reported to date. These findings confirm important quantitative differences between sexes in the O. erraticus saliva proteome, unveil novel salivary proteins and functions at the tick-host feeding interface and improve our understanding of the physiology of feeding in O. erraticus ticks. The integration of O. erraticus sialoproteomic and sialotranscriptomic data will drive a more rational selection of salivary candidates as antigen targets for the development of vaccines aimed at the control of O. erraticus infestations and the diseases it transmits.

Time-resolved proteomic profile of Amblyomma americanum tick saliva during feeding

Amblyomma americanum ticks transmit more than a third of human tick-borne disease (TBD) agents in the United States. Tick saliva proteins are critical to success of ticks as vectors of TBD agents, and thus might serve as targets in tick antigen-based vaccines to prevent TBD infections. We describe a systems biology approach to identify, by LC-MS/MS, saliva proteins (tick = 1182, rabbit = 335) that A. americanum ticks likely inject into the host every 24 h during the first 8 days of feeding, and towards the end of feeding. Searching against entries in GenBank grouped tick and rabbit proteins into 27 and 25 functional categories. Aside from housekeeping-like proteins, majority of tick saliva proteins belong to the tick-specific (no homology to non-tick organisms: 32%), protease inhibitors (13%), proteases (8%), glycine-rich proteins (6%) and lipocalins (4%) categories. Global secretion dynamics analysis suggests that majority (74%) of proteins in this study are associated with regulating initial tick feeding functions and transmission of pathogens as they are secreted within 24–48 h of tick attachment. Comparative analysis of the A. americanum tick saliva proteome to five other tick saliva proteomes identified 284 conserved tick saliva proteins: we speculate that these regulate critical tick feeding functions and might serve as tick vaccine antigens. We discuss our findings in the context of understanding A. americanum tick feeding physiology as a means through which we can find effective targets for a vaccine against tick feeding.

The lone star tick, Amblyomma americanum, is a medically important species in US that transmits 5 of the 16 reported tick-borne disease agents. Most recently, bites of this tick were associated with red meat allergies in humans. Vaccination of animals against tick feeding has been shown to be a sustainable and an effective alternative to current acaricide based tick control method which has several limitations. The pre-requisite to tick vaccine development is to understand the molecular basis of tick feeding physiology. Toward this goal, this study has identified proteins that A. americanum ticks inject into the host at different phases of its feeding cycle. This data set has identified proteins that A. americanum inject into the host within 24–48 h of feeding before it starts to transmit pathogens. Of high importance, we identified 284 proteins that are present in saliva of other tick species, which we suspect regulate important role(s) in tick feeding success and might represent rich source target antigens for a tick vaccine. Overall, this study provides a foundation to understand the molecular mechanisms regulating tick feeding physiology.

De novo transcriptome sequencing and comparative analysis of Haemaphysalis flava Neumann, 1897 at larvae and nymph stages

Haemaphysalis flava Neumann, 1897 (H. flava) is of public health significance due to its capability of transmitting several pathogens such as Rickettsia, Ehrlichia, Bartonella and Francisella tularensis. However, lack of complete genome, transcriptome and proteome information limits the understanding of the biology of H. flava. Here, the total RNA of H. flava was collected separately at larvae and nymph stages and analyzed with high-throughput RNA sequencing technology. The obtained data were assembled and annotated based on the near origin species in the Nr database. The functions of the unigenes were annotated and classified by seven databases, including Nr, Nt, Pfam, KOG, Swiss-Prot, GO and KEGG. A total of 61,850,967 and 79,579,368 clean reads were obtained with a data bulk of 9.28 G and 11.94 G in larvae and nymph stages, respectively. The number of unigenes was 440,896, with 48.6% of them being matched to the Nr database and 51.4% remaining unknown. Additionally, 1,776,404 SNPs were identified in the unigenes. Differential analysis revealed 80 differentially expressed genes (DEGs), including 56 up-regulated genes and 24 down-regulated genes in the nymph versus larvae. qPCR confirmed 4 of the 56 up-regulated genes and 4 of the down-regulated genes. KEGG analysis of the DEGs showed that aldehyde dehydrogenase and sorbitol dehydrogenase, two up-regulated unigenes in nymph versus larvae, were both matched to the top three enriched pathways: "chloroalkane and chloroalkene degradation", "fatty acid degradation" and "glycolysis and gluconeogenesis". This is the first report on the whole transcriptome of H. flava at larvae and nymph stages. This study contributes to the understanding of H. flava at the gene expression level in different developmental stages and provides a theoretical basis for the development of vaccines against H. flava.