Expression and functional analysis of Niemann-Pick C2 gene in Phytoseiulus persimilis

As a new protein class of semiochemical binding and transporting, Niemann-Pick proteins type C2 (NPC2) in arthropods have received more attentions in recent decade. However, the gene function has not been studied in phytoseiid mites with biocontrol potential. In the current study, we cloned a NPC2 gene PpNPC2a from the transcriptome of Phytoseiulus persimilis Athias-Henriot. By encoding 181 amino acids with a conserved ML domain, PpNPC2a was found a homolog of NPC2-1 in Galendromus occidentalis Nesbitt. We then measured the spatio-temporal expression of PpNPC2a in P. persimilis, and found the highest expression in female adults compared to other stages. Due to the tiny body size of predatory mites, we only examined tissue expressions in two sections: the anterior part (gnathosoma and the first pair of legs) and the posterior part (idiosoma without the first pair of legs). Higher transcription of PpNPC2a was found in the posterior part. To investigate the potential function of PpNPC2a in P. persimilis, we interfered gene expression in female adults by feeding dsRNA, which resulted in a decrease of relative expression by 59.1 and 78.2% after 24 and 72 h, respectively. Compared with the control, dsNPC2a-treated P. persimilis were insensitive to the scent of leaves or plants infested by spider mites, suggesting a role of PpNPC2a in response to plant volatiles. However, the dsNPC2a-interfered mites could still respond to four representative compounds of herbivore-induced plant volatiles, including 4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), methyl salicylate (MeSA), β-caryophyllene and linalool. In short, our results indicated PpNPC2a may be involved in the chemosensory process of P. persimilis in response to whole-plant volatiles.

Characterizing the Proliferation Patterns of Representative Microsporidian Species Enlightens Future Studies of Infection Mechanisms

Background: Microsporidia are a group of pathogens that infect all kinds of animals, such as humans, silkworms, honeybees, and shrimp; they, therefore, pose a severe threat to public health and the economy. There are over 1500 species of microsporidia that have been reported, among which Encephalitozoon hellem and Nosema bombycis are the representative zoonotic and insect-infecting species, respectively. Investigating their cell infection patterns is of great significance for understanding their infection mechanisms. Methods: Specific probes were designed for the ribosomal RNA sequences of microsporidia. Fluorescence in situ hybridization (FISH) was used to trace the proliferation cycle of the pathogens in different cells. Results: Here, two rRNA large subunit gene (LSUrRNA) probes specifically labeling N. bombycis were obtained. The life cycle of N. bombycis in silkworm cells and E. hellem in three kinds of host cells was graphically drawn. N. bombycis meronts were first observed at 30 hours post-infection (hpi), and they began merogony. Sporonts were observed at 42 hpi, and the first entire proliferation cycle was completed at 48 hpi. The proliferation cycle of E. hellem in RK13 and HEK293 epithelial cells was almost the same, completing the first life cycle after 24 hpi, but it was significantly delayed to 32 hpi in RAW264.7. Conclusions: Specific FISH probes were established for labeling microsporidia in multiple host cells. The proliferation characteristics of representative zoonotic and insect-infecting microsporidian species were clarified. This study provides an experimental pattern for future analyses of microsporidian infection mechanisms.

The NPC Families Mediate BmNPV Entry

Baculovirus is a powerful tool for biological control in agriculture and foreign gene expression and delivery in insect and mammalian cells. Baculovirus enters host cells by multiple endocytic pathways; however, the current understanding of the Bombyx mori nucleopolyhedrovirus (BmNPV) entry mechanism remains limited. Previous studies have identified NPC1 and NPC2 as important host factors for viral infection in insect cells, although their exact role in viral infection has not yet been determined. In this study, we demonstrate that the BmNPC1 protein is an important intracellular factor for BmNPV escape from the endosomal compartment, and the expression of BmNPC1 in Sf9 cells confers the virus the ability to enter into the nucleus of Sf9 cells. Additionally, the second luminal domain of BmNPC1 (BmNPC1-C) binds to the viral glycoprotein gp64, and preincubation of BmNPV with purified BmNPC1-C inhibits virus infection. Furthermore, knockout of the BmNPC2 protein results in reduced efficiency of viral fusion with the endosomal membrane, and BmNPC2 protein interacts directly with both viral envelope glycoprotein gp64 and the host BmNPC1 protein. BmNPC2 was found to be incorporated into progeny viral particles. Taken together, our results suggest that NPC2 protein incorporated into viral particles may facilitate viral infection through promoting the interaction of BmNPV and NPC1 in the endosome, thus enhancing viral fusion and escape from endosomes. These results, combined with those from previous studies, support that BmNPV hijacks two important cholesterol receptor members (NPC1 and NCP2) in the cholesterol intracellular transport pathway for viral entry into host cells.

IMPORTANCE Baculovirus is an important biological factor for controlling insect populations and represents a powerful biological tool for gene delivery and expression. However, the host receptor of baculovirus is still unknown. In this study, we demonstrate that BmNPC1 protein is an important intracellular factor for BmNPV escape from the endosomal compartment, and the expression of BmNPC1 confers the ability of virus to enter into the host cell nucleus in nonpermissive Sf9 cells. BmNPC2 can bind to the virus and promote progeny virion infection through the NPC1-NPC2 endosome cholesterol transport pathway. We believe that our study on the BmNPV entry mechanism will further facilitate the application of baculovirus systems in eukaryotic gene delivery. Not only can the cholesterol transport pathway NPC1 protein be used by a variety of enveloped viruses, but the NPC2 protein can also be used by viruses to infect host cells. This will provide new insights into the study of enveloped virus infection mechanisms.

Towards disrupting Varroa -honey bee chemosensing: A focus on a Niemann-Pick type C2 transcript

We focused our study on the 12 recently identified putative odorant carrier proteins in the ectoparasitic mite, Varroa destructor. Here we show, via an exclusion of the chemosensory appendages (forelegs and gnathosoma) that transcripts of five of the 12 genes were significantly lower, suggesting that they are likely involved in carrying host volatiles. Specifically, three transcripts were found to be foreleg-specific while the other two transcripts were expressed in both the forelegs and gnathosoma. We focused on one of the highly expressed and foreleg-specific transcript Vd40090, which encodes a Niemann-Pick disease protein type C2 (NPC2) protein. Effects of dsRNA-mediated silencing of Vd40090 were first measured by quantifying the transcript levels of genes that encode other putative odorant carrier proteins as well as reproduction related proteins. In addition, the impact of silencing on mites behaviour and survival was tested. Silencing of Vd40090 effectively disrupted Varroa host selection, acceptance and feeding and significantly impaired the expression of genes that regulate its reproduction in brood cells, resulting in reduced reproduction and survival.

Involvement of Chemosensory Protein BodoCSP1 in Perception of Host Plant Volatiles in Bradysia odoriphaga

Chemosensory proteins (CSPs) can bind and transport odorant molecules and play important roles in insect chemoreception. In this study, we focused on the roles of a chemosensory protein (BodoCSP1) in perception of host plant volatiles in Bradysia odoriphaga. The expression of BodoCSP1 was significantly higher in adults than in larvae and pupae, without a significant difference between male and female adults. Recombinant protein BodoCSP1 exhibited relatively high binding affinities to 9 out of 10 tested ligands (K_i < 10 μM). Behavioral assays revealed that adults of B. odoriphaga showed a significant preference for five compounds. The predicted three-dimensional (3D) structure of BodoCSP1 has the typical six α-helices that form the hydrophobic ligand-binding pocket. Molecular docking and site-directed mutagenesis combined with ligand-binding assays indicated that Val48 and Thr66 may be the key binding site in BodoCSP1 for host plant volatiles. RNAi results indicated that dsBodoCSP1-treated adults showed significant reductions in response to diallyl disulfide, dipropyl disulfide, and allyl methyl disulfide. These results indicated that BodoCSP1 plays essential functions in the perception of host plant volatiles in B. odoriphaga.

Identification of Leg Chemosensory Genes and Sensilla in the Apolygus lucorum

Apolygus lucorum (Hemiptera: Miridae), one of the main insect pests, causes severe damage in cotton and many other economic crops. As is well-known, legs play important roles in the chemoreception of insects. In this study, the putative chemosensory proteins in legs of A. lucorum involved in close or contact chemical communication of adult bugs were investigated using RNA transcriptome sequencing and qPCR methods. Transcriptome data of forelegs, middle legs and hind legs of adult bugs demonstrated that 20 odorant binding protein (OBP) genes, eight chemosensory protein (CSP) genes, one odorant receptor (OR) gene, one ionotropic receptor (IR) gene and one sensory neuron membrane protein (SNMP) gene were identified in legs of A. lucorum. Compared to the previous antennae transcriptome data, five CSPs, IR21a and SNMP2a were newly identified in legs. Results of qPCR analysis indicated that all these putative chemosensory genes were ubiquitously expressed in forelegs, middle legs and hind legs of bugs. Furthermore, four types of sensilla on legs of A. lucorum including sensilla trichodea (subtypes: long straight sensilla trichodea, Str1; long curved sensilla trichodea, Str2), sensilla chaetica (subtypes: sensilla chaetica 1, Sch1; sensilla chaetica 2, Sch2; and sensilla chaetica 3, Sch3), sensilla basiconca (subtypes: medium-long sensilla basiconca, Sba1; short sensilla basiconca, Sba2) and Böhm bristles (BB) were found using scanning electron microscopy. Additionally, the largest number of sensilla was observed on hind legs, while the forelegs had the smallest number of sensilla. Our data provide valuable insights into understanding the chemoreception of legs in A. lucorum.

Functional characterization of a Niemann-Pick type C2 protein in the parasitoid wasp Microplitis mediator

Niemann-Pick type C2 (NPC2) is a type of small soluble protein involved in lipid metabolism and triglyceride accumulation in vertebrates and arthropods. Recent studies have determined that NPC2 also participates in chemical communication of arthropods. In this work, two novel NPC2 proteins (MmedNPC2a and MmedNPC2b) in Microplitis mediator were identified. Real-time quantitative PCR (qPCR) analysis revealed that MmedNPC2a was expressed higher in the antennae than in other tissues of adult wasps compared with MmedNPC2b. Subsequent immunolocalization results demonstrated that NPC2a was located in the lymph cavities of sensilla placodea. To further explore the binding characterization of recombinant MmedNPC2a to 54 candidate odor molecules, a fluorescence binding assay was performed. It was found MmedNPC2a could not bind with selected fatty acids, such as linoleic acid, palmitic acid, stearic acid and octadecenoic acid. However, seven cotton volatiles, 4-ethylbenzaldehyde, 3,4-dimethylbenzaldehyde, β-ionone, linalool, m-xylene, benzaldehyde and trans-2-hexen-1-al showed certain binding abilities with MmedNPC2a. Moreover, the predicted 3D model of MmedNPC2a was composed of seven β-sheets and three pairs of disulfide bridges. In this model, the key binding residues for oleic acid in CjapNPC2 of Camponotus japonicus, Lue68, Lys69, Lys70, Phe97, Thr103 and Phe127, are replaced with Phe85, Ser86, His87, Leu113, Tyr119 and Ile143 in MmedNPC2a, respectively. We proposed that MmedNPC2a in M. mediator may play roles in perception of plant volatiles.

Genomic Reconstruction of the History of Native Sheep Reveals the Peopling Patterns of Nomads and the Expansion of Early Pastoralism in East Asia

China has a rich resource of native sheep (Ovis aries) breeds associated with historical movements of several nomadic societies. However, the history of sheep and the associated nomadic societies in ancient China remains poorly understood. Here, we studied the genomic diversity of Chinese sheep using genome-wide SNPs, mitochondrial and Y-chromosomal variations in > 1,000 modern samples. Population genomic analyses combined with archeological records and historical ethnic demographics data revealed genetic signatures of the origins, secondary expansions and admixtures, of Chinese sheep thereby revealing the peopling patterns of nomads and the expansion of early pastoralism in East Asia. Originating from the Mongolian Plateau ∼5,000‒5,700 years ago, Chinese sheep were inferred to spread in the upper and middle reaches of the Yellow River ∼3,000‒5,000 years ago following the expansions of the Di-Qiang people. Afterwards, sheep were then inferred to reach the Qinghai-Tibetan and Yunnan-Kweichow plateaus ∼2,000‒2,600 years ago by following the north-to-southwest routes of the Di-Qiang migration. We also unveiled two subsequent waves of migrations of fat-tailed sheep into northern China, which were largely commensurate with the migrations of ancestors of Hui Muslims eastward and Mongols southward during the 12th‒13th centuries. Furthermore, we revealed signs of argali introgression into domestic sheep, extensive historical mixtures among domestic populations and strong artificial selection for tail type and other traits, reflecting various breeding strategies by nomadic societies in ancient China.

Niemann-Pick disease type C2 protein induces autophagy and inhibits growth in FM3A breast cancer cells

Some peptides that are highly conserved between insects and mammals have anti-tumor action. Screening for inhibitors of cell growth from animal fluids may provide useful clues to anti-tumor drugs. Inducers of autophagy also have anti-tumor activity. The current authors recently studied a protein found in silkworm hemolymph, Niemann-Pick disease type C2 (NPC2). This protein, which is highly conserved among eukaryotes, was found to have anti-proliferative action on a silkworm cell line. The current study found that the silkworm NPC2 protein also inhibits the growth of FM3A murine breast cancer cells. In FM3A cells, silkworm NPC2 increased phosphorylation of AMP-activated protein kinase and decreased phosphorylation of Akt and mammalian target of rapamycin, which are regulators of autophagy. This study also found that NPC2 increased the amount of microtubule-associated protein light chain 3 (LC3)-II, an autophagosome marker, in FM3A cells. Silkworm NPC2 also induced an increase in the number of LC3-dots, a marker of pre-autophagic endosomes, in FM3A cells. When silkworm NPC2 was used to inhibit FM3A cell growth, that inhibition was attenuated by chloroquine, which inhibits autophagic activity by preventing lysosomal acidification. Murine NPC2 also inhibited growth and induced autophagy in FM3A cells. These findings suggest that NPC2 is involved in the induction and/or maintenance of autophagy and may help to elucidate the mechanisms underlying other neurodegenerative disorders such as Niemann-Pick disease.