Molecular characterization of vitellogenin and its receptor genes from citrus red mite, Panonychus citri (McGregor)

The TCTP is essential for ovarian development and oviposition of Rhipicephalus haemaphysaloides

Tick infestations transmit various infectious agents and result in significant socioeconomic consequences. Currently, the primary focus of tick control efforts is identifying potential targets for immune intervention. In a previous study, we identified a highly conserved protein abundant in tick haemolymph extracellular vesicles (EVs) known as translationally controlled tumour protein (TCTP). We have found that native TCTP is present in various tissues of the Rhipicephalus haemaphysaloides tick, including salivary glands, midgut, ovary, and fat body. Notably, TCTP is particularly abundant in the tick ovary and its levels increase progressively from the blood-feeding stage to engorgement. When the TCTP gene was knocked down by RNAi, there was a noticeable delay in ovarian development, and the reproductive performance, in terms of egg quantity and survival, was also hindered. Our investigations have revealed that the observed effects in ovary and eggs in dsRNA-treated ticks are not attributable to cell death mechanisms like apoptosis and autophagy but rather to the reduction in the expression of vitellogenin (Vg1, Vg2, and Vg3) and ferritin (ferritin 1 and ferritin 2) proteins crucial for ovarian development and embryo survival in ticks. Additionally, phylogenetic analysis and structural comparisons of RhTCTP and its orthologues across various tick species, vertebrate hosts, and humans have shown that TCTP is conserved in ticks but differs significantly between ticks and their hosts, particularly in the TCTP_1 and TCTP_2 domains. Overall, TCTP plays a vital role in tick reproductive development and presents itself as a potential target for tick control in both humans and animals.

Vitellogenin and its upstream gene TOR play essential roles in the reproduction of Dermanyssus gallinae

In Dermanyssus gallinae, a hematophagous mite, the initiation of vitellogenesis induced by blood feeding is essential for its reproduction. However, the precise gene structures and physiological functions of Vg in D. gallinae and its upstream gene, Target of Rapamycin (TOR), have not been fully understood. This study revealed the presence of four homologous genes within D. gallinae, named Dg-Vg1, Dg-Vg1-like, Dg-Vg2, and Dg-Vg2-like, especially, Dg-Vg2-like was firstly identified in the mites. The expression levels of all these Vg genes were significantly higher in adult females than other stages. Following blood feeding, the expression levels of these genes increased significantly, followed by a subsequent decrease, aligning with egg production. Silencing Dg-Vgs by RNA interference (RNAi) led to decreased fecundity and egg hatching rates, as well as abnormal embryonic development, suggesting a vital role for Dg-Vgs in both egg formation and embryonic development. Furthermore, the knockdown of Dg-TOR significantly reduced the expression of Dg-Vgs and negatively impacted the reproductive capabilities of PRMs, indicating that TOR influences PRM reproduction by regulating the expression of Dg-Vgs. In summary, these findings demonstrated the crucial roles of Dg-Vgs and Dg-TOR in PRM reproduction, highlighting their potential as targets for pest control.

Vitellogenin receptor transports the 30K protein LP1 without cell-penetrating peptide, into the oocytes of the silkworm, Bombyx mori

Vitellogenin receptors (VgRs) transport vitellogenin (Vg) into oocytes, thereby promoting egg growth and embryonic development. VgRs recognize and transport multiple ligands in oviparous animals, but their role in insects is rarely reported. In this study, we investigated whether Bombyx mori VgR (BmVgR) binds and transports lipoprotein-1 (BmLP1) and lipoprotein-7 (BmLP7) of the 30 kDa lipoproteins (30 K proteins), which are essential for egg formation and embryonic development in B. mori. Protein sequence analysis showed BmLP7, similar to reported lipoprotein-3 (BmLP3), contains the cell-penetrating peptides and Cysteine position, while BmLP1 has not. Assays using Spodoptera frugiperda ovary cells (sf9) indicated the direct entry of BmLP7 into the cells, whereas BmLP1 failed to enter. However, co-immunoprecipitation (Co-IP) assays indicated that BmVgR could bind BmLP1. Western blotting and immunofluorescence assays further revealed that over-expressed BmVgR could transport BmLP1 into sf9 cells. Co-IP assays showed that SE11C (comprising LBD1+EGF1+OTC domains of BmVgR) or SE22C (comprising LBD2+EGF2+OTC domains of BmVgR) could bind BmLP1. Over-expressed SE11C or SE22C could also transport BmLP1 into sf9 cells. Western blotting revealed that the ability of SE11C to transport BmLP1 might be stronger than that of SE22C. In the vit mutant with BmVgR gene mutation (vit/vit), SDS-PAGE and western blotting showed the content of BmLP1 in the ovary, like BmVg, was lower than that in the normal silkworm. When transgenic with hsp70 promoter over-expressed BmVgR in the vit mutant, we found that the phenotype of the vit mutant was partly rescued after heat treatment. And contents of BmLP1 and BmVg in vit mutant over-expressed BmVgR were higher than in the vit mutant. We conclude that BmVgR and its two repeat domains could bind and transport BmLP1 into the oocytes of the silkworm, besides BmVg. These results will provide a reference for studying the molecular mechanism of VgR transporting ligands in insects.

The importance of vitellogenin receptors in the oviposition of the pond wolf spider, Pardosa pseudoannulata

Vitellogenin receptor (VgR) is crucial for vitellogenin (Vg) uptake by oocytes. VgR is less known in Arachnida, especially in spiders. Different from only one VgR in an arthropod species, two VgRs, VgR-1 and VgR-2, were found in the pond wolf spider, Pardosa pseudoannulata. Both VgRs had the typical domains of the low-density lipoprotein receptor family except for the absence of the ligand-binding domain 1 in VgR-2. Spatiotemporal expression profiles showed that two VgR genes were consistently highly expressed in females and their ovaries, but VgR-1 was 48-fold that of VgR-2 in ovaries. The transcriptional level of VgR-1 was significantly downregulated by RNAi, but it did not work for VgR-2 although several trials were performed. Vg-1 and Vg-2 might be the ligands of VgR-1 because their expressions were also decreased in the dsVgR-1-treated females. Silencing VgR-1 prolonged the pre-oviposition period by 56 h. The expression of VgRs and Vgs were upregulated by juvenile hormones (JHs), which suggested that JHs were the essential factors to vitellogenesis in the spider. The present study revealed the importance of VgR-1 in the spider oviposition, which will improve the understanding on VgR physiological functions in spiders.

Insights into gene manipulation techniques for Acari functional genomics

Functional genomics is an essential tool for elucidating the structure and function of genes in any living organism. Here, we review the use of different gene manipulation techniques in functional genomics of Acari (mites and ticks). Some of these Acari species inflict severe economic losses to managed crops and health problems to humans, wild and domestic animals, but many also provide important ecosystem services worldwide. Currently, RNA interference (RNAi) is the leading gene expression manipulation tool followed by gene editing via the bacterial type II Clustered Regularly Interspaced Short Palindromic Repeats and associated protein 9 system (CRISPR-Cas9). Whilst RNAi, via siRNA, does not always lead to expected outcomes, the exploitations of the CRISPR systems in Acari are still in their infancy and are limited only to CRISP/Cas9 to date. In this review, we discuss the advantages and disadvantages of RNAi and CRISPR-Cas9 and the technical challenges associated with their exploitations. We also compare the biochemical machinery of RNAi and CRISPR-Cas9 technologies. We highlight some potential solutions for experimental optimization of each mechanism in gene function studies. The potential benefits of adopting various CRISPR-Cas9 systems for expanding on functional genomics experiments in Acari are also discussed.

Molecular characterization, expression pattern and RNAi-mediated silencing of vitellogenin receptor gene in almond moth, Cadra cautella

The almond moth is an important pest of date fruits worldwide. The females produce several eggs; however, role of vitellogenin receptor (VgR) in oocyte development by mediating endocytosis of major yolk protein precursor Vg remains yet unexplored. To investigate the role of vitellogenin receptor (VgR) in reproduction, Cadra cautella vitellogenin receptor (CcVgR) transcript was obtained using rapid amplification of cDNA ends-polymerase chain reaction. Expression analysis of CcVgR was performed using reverse transcriptase and quantitative polymerase chain reaction (qPCR) in different developmental stages. RNA interference was performed by injecting CcVgR-based double-stranded (ds)RNA at different exposure times. The results revealed that CcVgR is 5421 bp long, encoded 1807 amino acid, belongs to low-density lipoprotein receptor superfamily and contains all conserved domains. Expression analysis confirmed that CcVgR is sex-specific and starts to express in female larvae on day 19. Additionally, RNA interference (RNAi) of CcVgR-based dsRNA inhibited CcVgR expression up to 83% after 72 h, reduced fecundity and hatchability, and confirmed involvement of CcVgR in C. cautella reproduction. This report provides a basis for gene silencing in this species, and proposes RNAi technology potential for pest management.

Molecular approaches underlying the oogenic cycle of the scleractinian coral, Acropora tenuis

This study aimed to elucidate the physiological processes of oogenesis in Acropora tenuis. Genes/proteins related to oogenesis were investigated: Vasa, a germ cell marker, vitellogenin (VG), a major yolk protein precursor, and its receptor (LDLR). Coral branches were collected monthly from coral reefs around Sesoko Island (Okinawa, Japan) for histological observation by in situ hybridisation (ISH) of the Vasa (AtVasa) and Low Density Lipoprotein Receptor (AtLDLR) genes and immunohistochemistry (IHC) of AtVasa and AtVG. AtVasa immunoreactivity was detected in germline cells and ooplasm, whereas AtVG immunoreactivity was detected in ooplasm and putative ovarian tissues. AtVasa was localised in germline cells located in the retractor muscles of the mesentery, whereas AtLDLR was localised in the putative ovarian and mesentery tissues. AtLDLR was detected in coral tissues during the vitellogenic phase, whereas AtVG immunoreactivity was found in primary oocytes. Germline cells expressing AtVasa are present throughout the year. In conclusion, Vasa has physiological and molecular roles throughout the oogenic cycle, as it determines gonadal germline cells and ensures normal oocyte development, whereas the roles of VG and LDLR are limited to the vitellogenic stages because they act in coordination with lipoprotein transport, vitellogenin synthesis, and yolk incorporation into oocytes.

Molecular Characterization of Neoseiulus barkeri Vitellogenin Genes and Vitellogenin Receptor during Reproductive Diapause

The relationship between reproductive diapause and the genes related to vitellogenin (Vg) and its receptor (VgR) in insectoid ovarian development is still unclear. Accordingly, in the present study, we used hematoxylin and eosin staining to study the ovarian structure in the predatory mite Neoseiulus barkeri, a species that shows promise as a biological pest control agent. Staining revealed the presence of oocytes on ovary surfaces, and the oocytes were deposited as yolk granules through the intake of Vg and other nutrients with the development of the ovary. Development of the ovary stopped at the oocyte stage in diapausing adult mites, and this stage presented the same characteristics as the first day of adulthood in non-diapause female adults, where oocytes with nutrient cells, but no yolk granules are observed. In order to further explore the effects of the Vg gene and its receptor on reproduction, the sequences of the N. barkeri vitellogenin genes NbVg1, NbVg2, NbVg3, and NbVgR were analyzed using bioinformatics, and the expression levels of the NbVgs and the VgR at different developmental stages were determined by quantitative polymerase chain reaction (qPCR). The results showed that the NbVgs and NbVgR have complete domains and that the positions of many conservative regions and conservative motif are consistent. The expression levels of the NbVgs and NbVgR were highest in the ovipositional period, followed by those in the preovipositional period. The expression levels of the NbVgs and the VgR in non-diapause female adult mites were significantly higher than those in reproductive diapause female adult mites.

Molecular characterization of clathrin heavy chain (Chc) in Rhipicephalus haemaphysaloides and its effect on vitellogenin (Vg) expression via the clathrin-mediated endocytic pathway

Clathrin plays an important role in arthropods, but its function in ticks has not been explored. Here, we describe the molecular characteristics of the clathrin heavy chain of the tick Rhipicephalus haemaphysaloides and its effects on yolk development. The open reading frame of the clathrin heavy chain (Chc) (Rh-Chc) gene consists of 5103 nucleotides encoding 670 amino acids, which is most closely related to that of Ixodes scapularis and relatively close to Homo sapiens and Drosophila melanogaster. Real-time qPCR revealed that Rh-Chc was expressed at all developmental stages and organs. After Rh-Chc is silenced, ticks did not feed and mortality rate was 100%. Moreover, Rh-Chc co-localized with Vitellogenin receptor (VgR) on oocyte membrane. Immunofluorescence showed that the expression of Vitellogenin (Vg) (Rh-Vg) was also closely related to Rh-Chc. Immunofluorescence showed that the expression of Vg was also closely related to Rh-Chc, Rh-Chc silencing slowed the development of oocytes in tick, and culture of ovary in vitro silenced Rh-Chc, the development of oocytes in ticks also slowed down. Overall, the results of this study indicated that Rh-Chc is a vital gene in the tick R. haemaphysaloides that plays an important role in its growth, development, and reproduction.

Molecular Characterization of Vitellogenin and Its Receptor in Sogatella furcifera, and Their Function in Oocyte Maturation

The yolk protein precursor, vitellogenin (Vg), provides nutrition for embryonic development whereas the vitellogenin receptor (VgR) is responsible for the uptake of yolk protein by maturing oocytes. These two proteins are key reproduction-related proteins in insects. We cloned and characterized Vg and VgR genes in Sogatella furcifera, and investigated their function in oocyte maturation. Cloned SfVg and SfVgR have open reading frames of 6,114 and 5,796 bp, encoding 2,037 and 1,931 amino acid residues, respectively. Structural analysis indicates that SfVg has the three conserved LPD_N, DUF1943, and VWFD domains, SfVgR contains all conservative motifs of the LDLR superfamily. Both genes were highly expressed in adult females; SfVg was most highly expressed in the fat body whereas SfVgR was mainly expressed in the ovary. Knockdown of either gene reduced yolk protein deposition in oocytes and arrested oocyte maturation. However, silencing one of these two genes did not affect the transcript level of the other. These results demonstrate the role of SfVgR in transporting SfVg into oocytes. Both SfVg and SfVgR are essential for oocyte maturation in S. furcifera and both genes could potentially be targeted as means of controlling this pest.

Transcriptome analysis of the almond moth, Cadra cautella, female abdominal tissues and identification of reproduction control genes

Background

The almond moth, Cadra cautella is a destructive pest of stored food commodities including dates that causes severe economic losses for the farming community worldwide. To date, no genetic information related to the molecular mechanism/strategies of its reproduction is available. Thus, transcriptome analysis of C. cautella female abdominal tissues was performed via next-generation sequencing (NGS) to recognize the genes responsible for reproduction.

Results

The NGS was performed with an Illumina Hiseq 2000 sequencer (Beijing Genomics Institute: BGI). From the transcriptome data, 9,804,804,120 nucleotides were generated and their assemblage resulted in 62,687 unigenes. The functional annotation analyses done by different databases, annotated, 27,836 unigenes in total. The transcriptome data of C. cautella female abdominal tissue was submitted to the National Center for Biotechnology Information (accession no: PRJNA484692). The transcriptome analysis yielded several genes responsible for C. cautella reproduction including six Vg gene transcripts. Among the six Vg gene transcripts, only one was highly expressed with 3234.95 FPKM value (fragments per kilobase per million mapped reads) that was much higher than that of the other five transcripts. Higher differences in the expression level of the six Vg transcripts were confirmed by running the RT-PCR using gene specific primers, where the expression was observed only in one transcript it was named as the CcVg.

Conclusions

This is the first study to explore C. cautella reproduction control genes and it might be supportive to explore the reproduction mechanism in this pest at the molecular level. The NGS based transcriptome pool is valuable to study the functional genomics and will support to design biotech-based management strategies for C. cautella.

Molecular Characterization and Expression of Vitellogenin and Vitellogenin Receptor of Thitarodes pui (Lepidoptera: Hepialidae), an Insect on the Tibetan Plateau

Vitellogenin (Vg) and vitellogenin receptor (VgR) play important roles in the vitellogenesis of insects. In this study, we cloned and characterized the two corresponding genes (TpVg and TpVgR) in an economically important insect, Thitarodes pui (Lepidoptera: Hepialidae), from the Tibetan plateau. The full length of TpVg is 5566 bp with a 5373 bp open reading frame (ORF) encoding 1,790 amino acids. Sequence alignment revealed that TpVg has three conserved domains: a Vitellogenin_N domain, a DUF1943 domain, and a von Willebrand factor type D domain (VWD). The full length of TpVgR is 5732 bp, with a 5397 bp ORF encoding 1798 amino acids. BLASTP showed that TpVgR belongs to the low-density lipoprotein receptor (LDLR) gene superfamily. Structural analysis revealed that TpVgR has a group of four structural domains: a ligand-binding domain (LBD), an epidermal growth factor (EGF)-precursor homology domain, a transmembrane (TM) domain, and a cytoplasmic domain. In addition, TpVgR has four cysteine-rich LDL repeats in the first ligand-binding site and seven in the second. Quantitative real-time polymerase chain reaction analysis revealed that the expression levels of TpVg and TpVgR are much higher in later pupa than in either the larval or adult stage, implying that the synthesis and uptake of Vg in T. pui occurs in the later pupal stage. These results will help us to understand the molecular mechanism of the reproductive capacity and will provide new insight into the mass rearing and utilization of T. pui.

Biofunctional analysis of Vitellogenin and Vitellogenin receptor in citrus red mites, Panonychus citri by RNA interference

Panonychus citri is one of the most damaging pests of horticultural crops. Conventional control of this pest population through pesticides has led to the enhanced pest resistance. Management of P. citri population through RNAi, is still largely unknown. In oviparous organisms, fabrication and development of yolk protein play a vital role in the reproduction. Vitellin (Vn) is the source of eggs storage that helps in proper functioning of Vitellogenin (Vg) and Vitellogenin receptor (VgR). VgR is very compulsory protein for the development of Vg into oocytes. In the current study, Vg (PcVg) and VgR (PcVgR) genes were studied and their expressions at different developmental stages were quantified by RT-qPCR. Females treated with dsRNA of PcVg and PcVgR genes exhibited reduction in gene expression. Down regulation of target genes significantly effected oviposition and reduced the egg laying capacity up to 48% as compared to control (ds-egfp). Synergistic effect of target gene’s dsRNA was also accessed that reduced the egg laying up to 60.42%. Furthermore, combination of target dsRNA on deutonymph and protonymph also resulted in 67% and 70% reduction in eggs, respectively. Synergistic effect of dsRNA at 1000 ng/ul resulted in longer life span as compared to control treatments. This study suggests to develop a new strategy of P. citri population control by reducing its reproduction.

Transcriptomic information from Pacific white shrimp (Litopenaeus vannamei) ovary and eyestalk, and expression patterns for genes putatively involved in the reproductive process

The increased use of massive sequencing technologies has enabled the identification of several genes known to be involved in different mechanisms associated with reproduction that so far have only been studied in vertebrates and other model invertebrate species. In order to further investigate the genes involved in Litopenaeus vannamei reproduction, cDNA and SSH libraries derived from female eyestalk and gonad were produced, allowing the identification of expressed sequences tags (ESTs) that potentially have a role in the regulation of gonadal maturation. In the present study, different transcripts involved in reproduction were identified and a number of them were characterized as full-length. These transcripts were evaluated in males and females in order to establish their tissue expression profiles during developmental stages (juvenile, subadult and adult), and in the case of females, their possible association with gonad maturation was assessed through expression analysis of vitellogenin. The results indicated that the expression of vitellogenin receptor (vtgr) and minichromosome maintenance (mcm) family members in the female gonad suggest an important role during previtellogenesis. Additionally, the expression profiles of genes such as famet, igfbp and gpcr in brain tissues suggest an interaction between the insulin/insulin-like growth factor signaling pathway (IIS) and methyl farnesoate (MF) biosynthesis for control of reproduction. Furthermore, the specific expression pattern of farnesoic acid O-methyltransferase suggests that final synthesis of MF is carried out in different target tissues, where it is regulated by esterase enzymes under a tissue-specific hormonal control. Finally, the presence of a vertebrate type steroid receptor in hepatopancreas and intestine besides being highly expressed in female gonads, suggest a role of that receptor during sexual maturation.

Vitellogenin receptor selectively endocytoses female-specific and highly-expressed hemolymph proteins in the silkworm, Bombyx mori

VgR, a member of the LDLR family, functions to transport vitellogenin into the ovaries to protome ovarian growth and embryonic development. In insects, the only widely accepted ligand of VgR is Vg. Recently, BmVgR has been shown to interact with BmSP1 in vitro. Therefore, in this study, we evaluated whether BmVgR could transport BmSP1 into certain cells. Although BmVgR could combine with BmVg and BmSP1, BmVgR did not affect the amount of BmSP1 taken up by Sf9 cells. Parallel immunofluorescence showed that most BmVg and BmVgR were localized in the inner oocyte membrane, showing tissue localization similar to that of BmVg labeled with pHrodo Red absorbed by the ovaries on day 2 of pupation. Although BmSP1 showed localization similar to BmVgR during the same phase, little BmSP1 was present in the ovary. Additionally, BmSP1 did not exist in ovaries when the ovaries contained BmVgR on day 5 of pupation, suggesting that BmSP1 in the ovaries was not endocytosed by BmVgR. In summary, BmVgR could facilitate uptake of BmVg by developing oocytes, but did not modulate in the transport of BmSP1.

Molecular Characterization of Vitellogenin and Vitellogenin Receptor of Bemisia tabaci

Vitellogenin (Vg) plays vital role in oocytes and embryo development in insects. Vg is synthesized in the fat body, moves through haemolymph and accumulates in oocytes. Vitellogenin receptors (VgR) present on the surface of oocytes, are responsible for Vg transportation from haemolymph to oocytes. Here, we cloned and characterized these genes from Bemisia tabaci Asia1 (BtA1) species. The cloned BtA1Vg and BtA1VgR genes consisted of 6,330 and 5,430 bp long open reading frames, which encoded 2,109 and 1,809 amino acid (AA) residues long protein. The BtA1Vg protein comprised LPD_N, DUF1943 and VWFD domains, typical R/KXXR/K, DGXR and GL/ICG motifs, and polyserine tracts. BtA1VgR protein contained 12 LDLa, 10 LDLb and 7 EGF domains, and a trans-membrane and cytoplasmic region at C-terminus. Phylogenetic analyses indicated evolutionary association of BtA1Vg and BtA1VgR with the homologous proteins from various insect species. Silencing of BtA1VgR by siRNA did not affect the transcript level of BtA1Vg. However, BtA1Vg protein accumulation in oocytes was directly influenced with the expression level of BtA1VgR. Further, BtA1VgR silencing caused significant mortality and reduced fecundity in adult whiteflies. The results established the role of BtA1VgR in transportation of BtA1Vg in oocytes. Further, these proteins are essential for fecundity, and therefore these can be potential RNAi targets for insect control in crop plants.

The Essential Role of Vitellogenin Receptor in Ovary Development and Vitellogenin Uptake in Bactrocera dorsalis (Hendel)

The vitellogenin receptor (VgR) functions as an essential component in uptaking and transporting vitellogenin (Vg) in female adults, which is involved in ovary development and oviposition. This study aimed to clarify the molecular characteristics and function of VgR in the oriental fruit fly Bactrocera dorsalis (Hendel). Here, we identified the full-length of BdVgR (GenBank Accession No. JX469118), encoding a 1925 residue (aa) protein with a 214.72 kDa molecular mass and several typical motifs of low-density lipoprotein receptor superfamily (LDLR). Phylogenic analysis suggested that BdVgR was evolutionary conserved with other Dipteran VgRs. The expression of BdVgR was exclusively detected in the ovaries rather than head, thorax or other tissues. The developmental expression patterns showed that the signal of BdVgR was detectable in very beginning of adult stage, and positively correlated with the growth rate of ovaries and the expression levels of its ligands. In addition, we also demonstrated that the expression level of BdVgR, and ovary development were significantly suppressed after being injected with BdVgR-targeted dsRNA. Together, all of these results indicated that BdVgR was critical for yolk protein absorption and ovary maturation in B. dorsalis, playing a vital role in female reproduction.