Cloning and characterization of a ribosomal protein L24 from Haemaphysalis longicornis eggs

A Novel MicroRNA and the Target Gene TAB2 Can Regulate the Process of Sucking Blood in and the Spawn Rate of Hyalomma asiaticum (Acari: Ixodidae) Ticks

Ticks are blood-sucking parasites that are harmful to humans and animals. MicroRNAs are a class of conserved small noncoding RNAs that play regulatory roles in the expression of many genes at the posttranscriptional level. Here, a novel miRNA (nov-miR-17) was identified from a small RNA data library of Hyalomma asiaticum by next-generation sequencing. PCR was used to obtain precursor nov-miR-17 by RACE using mature loop primers. The secondary structure was predicted with UNAFold. The interaction of nov-miR-17 with its target gene TAB2 was predicted using RNAhybrid software and identified in vitro by luciferase assays. Moreover, the interaction was confirmed in vivo by phenotype rescue experiments in which dsTAB2 was used for RNA interference (RNAi) and an antagomir of nov-miR-17 was used for miRNA silencing. The expression levels of nov-miR-17 and TAB2 in ticks at different developmental stages and the expression of nov-miR-17 in different tissues were analyzed by real-time qPCR. All data were analyzed using GraphPad Prism version 5. Results: The results showed that TAB2 was a target gene of nov-miR-17. When the blood-sucking process of larval, nymph and adult ticks was prolonged, the expression of nov-miR-17 was decreased, and TAB2 expression was increased. However, the level of nov-miR-17 in the midgut of engorged ticks was highest at all stages. Therefore, nov-miR-17 plays an important role in the blood-sucking process. The overexpression of nov-miR-17 indicated that this miRNA affected the engorged weight (P < 0.001) and spawn rate (P < 0.001) of female ticks. RNAi of TAB2 also had the same effect. dsRNA not only impacted the weight (P < 0.01) but also reduced the spawn rate (P < 0.001) of the ticks. Furthermore, significant recovery was observed in nov-miR-17-silenced ticks after TAB2 silencing by RNAi. nov-miR-17 silencing by antagomir not only impacted the engorged weight of the female ticks (P < 0.001) but also the number of days that the females needed to progress from engorgement to spawning (P < 0.001). The study showed that nov-miR-17, as a new miRNA, plays an important role along with its target gene TAB2 in the blood-sucking and spawning processes in female ticks.

Identification of ribosomal protein L24 (RPL24) from the oriental river prawn, Macrobrachium nipponense, and its roles in ovarian development

Ribosomal proteins exhibit various extraribosomal functions in addition to their roles in protein synthesis. In this study, complementary DNA (cDNA) of ribosomal protein L24 in Macrobrachium nipponense (MnRPL24) was isolated, and its role in ovarian development was investigated using quantitative real-time PCR (qPCR), immunohistochemistry (IHC), RNA interference (RNAi) and histological observations. The complete cDNA of MnRPL24 is 564 base pairs (bps) and contains a 486 bp open reading frame (ORF) encoding 162 amino acids (aas). The highest expression level of MnRPL24 among eight tissues was found in the ovary, specifically in the stage I ovary. The MnRPL24 protein existed in the cytoplasm and nucleus of developing oocytes, and also existed in the cytoplasm of follicle cells in developing ovaries. After MnRPL24 knockdown by RNAi, the expression levels of vitellogenin (Vg), vitellogenin receptor (Vgr), cyclin-dependent kinase 2 (Cdc2) and M-phase cyclin (Cyclin B) genes and the gonadsomatic index (GSI) did not show the typical trend of gradually elevation with ovarian development and finally decrease in the later stage of ovarian cycle. Moreover, the oviposition rate (OR) was downregulated, and oocyte development was delayed after MnRPL24 knockdown. After eyestalk ablation, the MnRPL24 expression level was considerably elevated in the initial stages and decreased in the late stage of the ovarian development cycle. This investigation illustrates a possible regulatory role of MnRPL24 in the ovarian development of M. nipponense, and MnRPL24 may act as a stimulator of early ovarian development.

Characterization of an MLP Homologue from Haemaphysalis longicornis (Acari: Ixodidae) Ticks

Members of the cysteine-rich protein (CRP) family are known to participate in muscle development in vertebrates. Muscle LIM protein (MLP) belongs to the CRP family and has an important function in the differentiation and proliferation of muscle cells. In this study, the full-length cDNA encoding MLP from Haemaphysalis longicornis (H. longicornis; HLMLP) ticks was obtained by 5' rapid amplification of cDNA ends (RACE). To verify the transcriptional status of MLP in ticks, HLMLP gene expression was assessed during various developmental stages by real-time PCR (RT-PCR). Interestingly, HLMLP expression in the integument was significantly (P < 0.01) higher than that observed in other tested tissues of engorged adult ticks. In addition, HLMLP mRNA levels were significantly downregulated in response to thermal stress at 4 °C for 48 h. Furthermore, recombinant HLMLP was expressed in Escherichia coli, and Western blot analysis showed that rabbit antiserum against H. longicornis adults recognized HLMLP and MLPs from different ticks. Ten 3-month-old rabbits that had never been exposed to ticks were used for the immunization and challenge experiments. The rabbits were divided into two groups of five rabbits each, where rabbits in the first group were immunized with HLMLP, while those in the second group were immunized with phosphate-buffered saline (PBS) diluent as controls. The vaccination of rabbits with the recombinant HLMLP conferred partial protective immunity against ticks, resulting in 20.00% mortality and a 17.44% reduction in the engorgement weight of adult ticks. These results suggest that HLMLP is not ideal as a candidate for use in anti-tick vaccines. However, the results of this study generated novel information on the MLP gene in H. longicornis and provide a basis for further investigation of the function of this gene that could potentially lead to a better understanding of the mechanism of myofiber determination and transformation.

MicroRNA let-7 regulates the expression of ecdysteroid receptor (ECR) in Hyalomma asiaticum (Acari: Ixodidae) ticks

Background

Ticks are blood-sucking arthropods that can transmit diseases to humans and animals. These arthropods are the second most important vectors of pathogens. MicroRNAs are a class of conserved small noncoding RNAs that play regulatory roles in gene expression at the post-transcriptional level. Molting is an important biological process in arthropods. Research on the molting process is important for understanding tick physiology and control.

Methods

Dual-luciferase reporter assays were used to assess the role of miRNA let-7 in ecdysteroid receptor (ECR) biology. The expression levels of ECR and let-7 were measured by real-time qPCR before and after tick molting. To explore the function of let-7 and ECR, we performed overexpression and knocking down of let-7 and RNAi of ECR in tick nymphs. The biological function of let-7 in molting was explored by injecting nymphs, ten days after engorgement, with let-7 agomir for overexpression and let-7 antagomir for knocking down. The rate of molting was then determined. ECR dsRNA was injected into ticks to evaluate the function of ECR by gene silencing. The expression of ECR and let-7 was measured using RT-qPCR. All data were analyzed using GraphPad Prism v.6.

Results

The results of the luciferase assay using a eukaryotic expression system revealed that ECR was a natural target of let-7. Let-7 overexpressed by agomir affected the rate of molting (P < 0.01) and the period of molting (P < 0.01). Let-7 antagomir for knockdown affected the period of molting (P < 0.01), but there was no effect on the rate of molting (P = 0.27). ECR dsRNA gene silencing significantly affected the rate of molting (P < 0.05).

Conclusions

This study demonstrated that let-7 can regulate the expression of ECR and that let-7 can affect molting in ticks. Our results help to understand the regulation of let-7 by 20-hydroxyecdysone (20E) and will provide a reference for functional analysis studies of microRNAs in ticks.

Primary characterization of a putative novel TBC1 domain family member 13 from Haemaphysalis qinghaiensis

A putative novel TBC1 domain family member 13 (HqTBC1D13) from Haemaphysalis qinghaiensis was cloned using rapid amplification of the cDNA ends (RACE), the HqTBC1D13 cDNA is 1702bp in length and encodes 396 amino acid residues with predicted molecular weight of 46.09kDa. The TBC-domain containing protein has a catalytic 'arginine finger' analogous to those of Ras and Rho family GAPs, which is critical determinants of GAP activity. The amino acid sequences of TBC domain were evolutionarily highly conserved across species. The partial coding sequence of HqTBC1D13 with the predicted molecular weight of 37.2kDa was expressed and purified in the PGEX-4T-1 vector. Real-time RT PCR analysis showed that the HqTBC1D13 was extensively expressed in the tested organs (salivary glands, midguts, ovaries and cuticles), and its transcriptional levels in salivary glands were significantly up-regulate induced by blood-feeding. The recombinant HqTBC1D13 protein vaccination in the rabbit model resulted in the extension of the duration of feeding and the reduction of 37% female engorgement and 14.8% oviposition compared to the control group. These results indicated that the HqTBC1D13 in ticks could be invovled in the regulation of feeding and oviposition.

Characterization of acid phosphatase from the tick Haemaphysalis longicornis

The full-length cDNA encoding acid phosphatase (HL-3) from Haemaphysalis longicornis was obtained by 5' rapid amplification of cDNA ends (RACE). The cDNA contained a 1137 bp open reading frame (ORF) coding for 356 amino acids with a predicted theoretical isoelectric point (pI) of 6.35 and molecular weight of 41.0 kDa. The recombinant protein was expressed in Escherichia coli. The enzyme could hydrolyze para-nitrophenyl phosphate (pNPP) substrate at an optimum pH of 5.0. Real-time RT-PCR analysis showed that the HL-3 transcripts were expressed in various stages of unfed ticks and were significantly induced by blood feeding. Furthermore, the expression of HL-3 in midguts was significantly higher than in other tested tissues of partially fed adult ticks. The transcripts of the HL-3 mRNA in lipopolysaccharide (LPS)-injected ticks were 1.75 times of the PBS-injected control; Theileria sergenti infected larvae expressed 3.86 more times than that of uninfected ones. Western blot analysis showed that rabbit antiserum against the recombinant rHL-3 could recognize a native protein of approximately 41.0 kDa in the lysates from different stages of ticks. Vaccination of rabbits with the rHL-3 conferred partial protective immunity against ticks, resulting in 28% mortality and 10.6% reduction in engorgement weight of adult ticks, respectively. These results suggested that the HL-3 was involved in tick innate immunity and could be used as a potential candidate antigen for the development of anti-tick vaccines.

Identification of the heat shock protein 70 (HLHsp70) in Haemaphysalis longicornis

A Haemaphysalis longicornis heat shock protein 70 (HLHsp70) was identified from a cDNA library synthesized from tick eggs. The HLHsp70 cDNA is 2311 bp in length and encodes 661 amino acid residues with the predicted molecular weight of 72.5 kDa and an isoelectronic point (pI) of 5.2. It also contains the highly conserved functional motifs of the Hsp70 family and a specific endoplasmic reticulum (ER) retention signal "KDEL" that is common among ER-localized proteins. The HLHsp70 exhibits 90% amino acid identity to the putative Hsp70 of Ixodes scapularis, and 85% to Gallus gallus 78 kDa glucose-regulated protein precursor. Real time RT-PCR analysis showed that the expression levels of the Hsp70 in ovaries and salivary glands were significantly higher than in other tested tissues in partially fed females. Although the expression level of the HLHsp70 was constantly low in unfed ticks, it was significantly induced by blood-feeding. Further, the expression was positively correlated to the temperature (4-37°C, tested). Western blot analysis showed that the rabbit antiserum against the recombinant HLHsp70 protein (rHLHSP70) recognized bands of approximately 100, 72, and 28 kDa from egg lysates, as well as a 72kDa fragment in protein extracts from partially fed larvae. Immunization of rabbits with the rHLHSP70 did not result in a statistically significant reduction of female tick engorgement and oviposition. These results suggest that although HLHSP70 plays a role in the physiological activities of ticks, as a constitutive protein it was not suitable for selection as a candidate vaccine antigen against ticks.