Three vital RNA functions and interactions in the process of silk gland apoptosis in silkworm Bombyx mori.

The Silkworm Bombyx mori is an important insect in terms of economics and a model organism with a complete metamorphosis. The economic importance of silkworms is dependent on the functions of the silkgland, a specialized organ that synthesizes silk proteins. The silk gland undergoes massive degeneration during the larval to pupal stage, which involves in cell apoptosis. In this paper, high throughput sequencing was used to detect the expression of messenger RNA (mRNA), long noncoding RNA (lncRNA), and microRNA (miRNA) from silk glands of Day 3 in the fifth instar larvae (L5D3) and the spinning 36h (sp36h). We analyzed the Gene Ontology (GO) functions of target genes of the differentially expressed lncRNAs and miRNAs. We investigated the regulations of mRNA, lncRNA, and miRNA on silk gland apoptosis in L5D3 and sp36h. In total, 10,947 lncRNAs were detected in the silk gland and the index number TCONS-00021360 lncRNA may be involved in the process of apoptosis. In addition, 344 miRNAs targeted 285 mRNAs were related to the death process under GO entry. The results indicated that miRNAs play an important role in the molecular regulation of the silk gland apoptosis compared with that of lncRNAs. Finally, we screened 746 lncRNAs and 20 miRNAs that might interact with BmDredd, and drew an interaction network among them.

Role of BmDredd during Apoptosis of Silk Gland in Silkworm, Bombyx mori.

Silk glands (SGs) undergo massive apoptosis driven degeneration during the larval-pupal transformation. To better understand this event on molecular level, we investigated the expression of apoptosis-related genes across the developmental transition period that spans day 4 in the fifth instar Bombyx mori larvae to day 2 pupae. Increases in the expression of BmDredd (an initiator caspase homolog) closely followed the highest BmEcR expression and resembled the expression trend of BmIcE. Simultaneously, we found that BmDredd expression was significantly higher in SG compared to other tissues at 18 h post-spinning, but reduced following injection of the apoptosis inhibitor (Z-DEVD-fmk). Furthermore, BmDredd expression correlated with changes of caspase3-like activities in SG and RNAi-mediated knockdown of BmDredd delayed SG apoptosis. Moreover, caspase3-like activity was increased in SG by overexpression of BmDredd. Taken together, the results suggest that BmDredd plays a critical role in SG apoptosis.

BMDREDD REGULATES THE APOPTOSIS COORDINATING WITH BMDAXX, BMCIDE-B, BMFADD, AND BMCREB IN BMN CELLS.

The apoptosis mechanisms in mammals were investigated relatively clearly. However, little is known about how apoptosis is achieved at a molecular level in silkworm cells. We cloned a caspase homologous gene named BmDredd (where Bm is Bombyx mori and Dredd is death-related ced-3/Nedd2-like caspase) in BmN cells from the ovary of Bm and analyzed its biological information. We constructed the N-terminal, C-terminal, and overexpression vector of BmDredd, respectively. Our results showed that the transcriptional expression level of BmDredd was increased in the apoptotic BmN cells. Furthermore, overexpression of BmDredd increased the caspase-3/7 activity. Simultaneously, RNAi of BmDredd could save BmN cells from apoptosis. The immunofluorescence study showed that BmDredd located at the cytoplasm in normal cell otherwise is found at the nucleus when cells undergo apoptosis. Moreover, we quantified the transcriptional expressions of apoptosis-related genes including BmDredd, BmDaxx (where Daxx is death-domain associated protein), BmCide-b (where Cide-b is cell death inducing DFF45-like effector), BmFadd (Fadd is fas-associated via death domain), and BmCreb (where Creb is cAMP-response element binding protein) in BmN cells with dsRNA interferences to detect the molecular mechanism of apoptosis. In conclusion, BmDredd may function for promoting apoptosis and there are various regulatory interactions among these apoptosis-related genes.

ECDYSTEROID AND CHITINASE FLUCTUATIONS IN THE WESTERN TARNISHED PLANT BUG (Lygus hesperus) PRIOR TO MOLT INDICATE ROLES IN DEVELOPMENT.

Vital physiological processes that drive the insect molt represent areas of interest for the development of alternative control strategies. The western tarnished plant bug (Lygus hesperus Knight) is a pest of numerous agronomic and horticultural crops but the development of novel control approaches is impeded by limited knowledge of the mechanisms regulating its molt. To address this deficiency, we examined the fundamental relationship underlying the hormonal and molecular components of ecdysis. At 27°C L. hesperus exhibits a temporally controlled nymph-adult molt that occurs about 4 days after the final nymph-nymph molt with ecdysteroid levels peaking 2 days prior to the final molt. Application of exogenous ecdysteroids when endogenous levels had decreased disrupted the nymphal-adult molt, with treated animals exhibiting an inability to escape the old exoskeleton and resulting in mortality compared to controls. Using accessible transcriptomic data, we identified 10 chitinase-like sequences (LhCht), eight of which had protein motifs consistent with chitinases. Phylogenetic analyses revealed orthologous relationships to chitinases critical to molting in other insects. RT-PCR based transcript profiling revealed that expression changes to four of the LhChts was coordinated with the molt period and ecdysteroid levels. Collectively, our results support a role for ecdysteroid regulation of the L. hesperus molt and suggest that cuticle clearance is mediated by LhCht orthologs of chitinases that are essential to the molt process. These results provide the initial hormonal and molecular basis for future studies to investigate the specific roles of these components in molting.

BmPLA2 containing conserved domain WD40 affects the metabolic functions of fat body tissue in silkworm, Bombyx mori.

PLA2 enzyme hydrolyzes arachidonic acid, and other polyunsaturated fatty acids, from the sn-2 position to release free arachidonic acid and a lysophospholipid. Previous studies reported that the PLA2 in invertebrate organisms participates in lipid signaling molecules like arachidonic acid release in immune-associated tissues like hemocytes and fat bodies. In the present study, we cloned the BmPLA2 gene from fat body tissue of silkworm Bombyx mori, which has a total sequence of 1.031 kb with a 31.90 kDa protein. In silico results of BmPLA2 indicated that the protein has a putative WD40 conserved domain and its phylogeny tree clustered with Danaus plexippus species. We investigated the transcriptional expression in development stages and tissues. The highest expression of BmPLA2 was screened in fat body among the studied tissues of third day fifth instar larva, with a high expression on third day fifth instar larva followed by a depression of expression in the wandering stage of the fifth instar larva. The expression of BmPLA2 in female pupa was higher than that of male pupa. Our RNAi-mediated gene silencing results showed highest reduction of BmPLA2 expression in post-24 h followed by post-48 and post-72 h. The BmPLA2-RNAi larvae and pupa could be characterized by pharate adult lethality and underdevelopment. The phenotypic characters of fat body cells in RNAi-induced larva implied that BmPLA2 affects the metabolic functions of fat body tissue in silkworm Bombyx mori.

TRANSCRIPTION FACTOR Bmsage PLAYS A CRUCIAL ROLE IN SILK GLAND GENERATION IN SILKWORM, Bombyx mori.

Salivary gland secretion is altered in Drosophila embryos with loss of function of the sage gene. Saliva has a reduced volume and an increased electron density according to transmission electron microscopy, resulting in regions of tube dilation and constriction with intermittent tube closure. However, the precise functions of Bmsage in silkworm (Bombyx mori) are unknown, although its sequence had been deposited in SilkDB. From this, Bmsage is inferred to be a transcription factor that regulates the synthesis of silk fibroin and interacts with another silk gland-specific transcription factor, namely, silk gland factor-1. In this study, we introduced a germline mutation of Bmsage using the Cas9/sgRNA system, a genome-editing technology, resulting in deletion of Bmsage from the genome of B. mori. Of the 15 tested samples, seven displayed alterations at the target site. The mutagenesis efficiency was about 46.7% and there were no obvious off-target effects. In the screened homozygous mutants, silk glands developed poorly and the middle and posterior silk glands (MSG and PSG) were absent, which was significantly different from the wild type. The offspring of G0 mosaic silkworms had indel mutations causing 2- or 9-bp deletions at the target site, but exhibited the same abnormal silk gland structure. Mutant larvae containing different open-reading frames of Bmsage had the same silk gland phenotype. This illustrated that the mutant phenotype was due to Bmsage knockout. We conclude that Bmsage participates in embryonic development of the silk gland.

RNAi KNOCKDOWN OF BmRab3 LED TO LARVA AND PUPA LETHALITY IN SILKWORM Bombyx mori L.

Rab3 GTPases are known to play key a role in vesicular trafficking, and express highest in brain and endocrine tissues. In mammals, Rab3 GTPases are paralogs unlike in insect. In this study, we cloned Rab3 from the silk gland tissue of silkworm Bombyx mori, and identified it as BmRab3. Our in silico analysis indicated that BmRab3 is an isoform with a theoretical isoelectric point and molecular weight of 5.52 and 24.3 kDa, respectively. Further, BmRab3 showed the C-terminal hypervariability for GGT2 site but having two other putative guanine nucleotide exchange factor/GDP dissociation inhibitor interaction sites. Multiple alignment sequence indicated high similarities of BmRab3 with Rab3 isoforms of other species. The phylogeny tree showed BmRab3 clustered between the species of Tribolium castaneum and Aedes aegypti. Meanwhile, the expression analysis of BmRab3 showed the highest expression in middle silk glands (MSGs) than all other tissues in the third day of fifth-instar larva. Simultaneously, we showed the differential expression of BmRab3 in the early instar larva development, followed by higher expression in male than female pupae. In vivo dsRNA interference of BmRab3 reduced the expression of BmRab3 by 75% compared to the control in the MSGs in the first day. But as the worm grew to the third day, the difference of BmRab3 between knockdown and control was only about 10%. The knockdown later witnessed underdevelopment of the larvae and pharate pupae lethality in the overall development of silkworm B. mori L.

Hedgehog signaling pathway regulated the target genes for adipogenesis in silkworm Bombyx mori.

Hedgehog (Hh) signals regulate invertebrate and vertebrate development, yet the role of the pathway in adipose development remains poorly understood. In this report, we found that Hh pathway components are expressed in the fat body of silkworm larvae. Functional analysis of these components in a BmN cell line model revealed that activation of the Hh gene stimulated transcription of Hh pathway components, but inhibited the expression of the adipose marker gene AP2. Conversely, specific RNA interference-mediated knockdown of Hh resulted in increased AP2 expression. This further showed the regulation of Hh signal on the adipose marker gene. In silkworm larval models, enhanced adipocyte differentiation and an increase in adipocyte cell size were observed in silkworms that had been treated with a specific Hh signaling pathway antagonist, cyclopamine. The fat-body-specific Hh blockade tests were consistent with Hh signaling inhibiting silkworm adipogenesis. Our results indicate that the role of Hh signaling in inhibiting fat formation is conserved in vertebrates and invertebrates.

piggyBac transposon-derived targeting shRNA interference against the Bombyx mori nucleopolyhedrovirus (BmNPV).

The Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the most destructive diseases in silkworm, which has caused the main damage to sericulture industry. In this study, we developed a system of RNAi to prevent the BmNPV infection using the piggyBac transposon-derived targeting short hairpin RNA (shRNA) interference. The shRNAs targeting the genes of i.e.-1, lef-1, lef-2 and lef-3 of BmNPV were designed and used to inhibit the intracellular replication or multiplication of BmNPV in Bm cells. The highest activity was presented in the shRNA targeting the i.e.-1c of BmNPV, of which the inhibition rate reached 94.5 % in vitro. Further a stable Bm cell line of piggyBac transposon-derived targeting shRNA interference against BmNPV was established, which has a highly efficacious suppression on virus proliferation. These results indicated that the recombinant shRNA expression system was a useful tool for resistance to BmNPV in vitro. The approach by recombinant shRNAs opens a door of RNAi technology as a strategy that offering technically simpler, cheaper, and quicker gene knockdown for promising research and biotechnology application on silkworm lethal diseases.

Molecular cloning and transcription expression of 3-dehydroecdysone 3α-reductase (3de 3α-reductase) in the different tissues and the developing stage from the silkworm, Bombyx mori L.

Molting in insects is regulated by molting hormones (ecdysteroids), which are also crucial to insect growth, development, and reproduction etc. The decreased ecdysteroid in titre results from enhanced ecdysteroid inactivation reactions including the formation of 3-epiecdyson under ecdysone oxidase and 3-dehydroecdysone 3α-reductase (3DE 3α-reductase). In this paper, we cloned and characterized 3-dehydroecdysone 3α-reductase (3DE 3α-reductase) in different tissues and developing stage of the silkworm, Bombyx mori L. The B. mori 3DE 3α-reductase cDNA contains an ORF 783 bp and the deduced protein sequence containing 260 amino acid residues. Analysis showed the deduced 3DE 3α-reductase belongs to SDR family, which has the NAD(P)-binding domain. Using the Escherichia coli, a high level expression of a fusion polypeptide band of approx. 33 kDa was observed. High transcription of 3DE 3α-reductase was mainly presented in the midgut and hemolymph in the third day of fifth instar larvae in silkworm. The expression of 3DE 3α-reductase at different stages of larval showed that the activity in the early instar was high, and then reduced in late instar. This is parallel to the changes of molting hormone titer in larval. 3DE 3α-reductase is key enzyme in inactivation path of ecdysteroid. The data elucidate the regulation of 3DE 3α-reductase in ecdyteroid titer of its targeting organs and the relationship between the enzyme and metamorphosis.

Expression and functions of dopa decarboxylase in the silkworm, Bombyx mori was regulated by molting hormone.

Insect molting is an important developmental process of metamorphosis, which is initiated by molting hormone. Molting includes the activation of dermal cells, epidermal cells separation, molting fluid secretion, the formation of new epidermis and old epidermis shed and other series of continuous processes. Polyphenol oxidases, dopa decarboxylase and acetyltransferase are necessary enzymes for this process. Traditionally, the dopa decarboxylase (BmDdc) was considered as an enzyme for epidermal layer's tanning and melanization. This work suggested that dopa decarboxylase is one set of the key enzymes in molting, which closely related with the regulation of ecdysone at the time of biological molting processes. The data showed that the expression peak of dopa decarboxylase in silkworm is higher during molting stage, and decreases after molting. The significant increase in the ecdysone levels of haemolymph was also observed in the artificially fed silkworm larvae with ecdysone hormone. Consistently, the dopa decarboxylase expression was significantly elevated compared to the control. BmDdc RNAi induced dopa decarboxylase expression obviously declined in the silkworm larvae, and caused the pupae appeared no pupation or incomplete pupation. BmDdc was mainly expressed and stored in the peripheral plasma area near the nucleus in BmN cells. In larval, BmDdc was mainly located in the brain and epidermis, which is consisted with its function in sclerotization and melanization. Overall, the results described that the dopa decarboxylase expression is regulated by the molting hormone, and is a necessary enzyme for the silkworm molting.

Characterization of adaptor protein complex-1 in the silkworm, Bombyx mori.

To investigate the function of adaptor protein complex-1 (AP-1) in the silkworm, we characterized AP-1 in the silkworm by RNAi technique and co-localization methods. As a result, AP-1 was found to exist as cytosolic form and membrane-bound form distinguished by phosphate status, showing molecular mass difference. There was relatively more cytosolic form of AP-1 than its membrane-bound counterpart in the silkworm. However, AP-1 distributed predominantly as cytosolic form in BmN cells. Interruption of AP-1 expression via DsRNA was more efficient in BmN cells than in the insect larval, which led to a tendency to dissociation between subcellular organelles like the Golgi apparatus and the mitochondria. Environmental condition changes like relatively higher temperature and treatment with dimethyl sulfoxide can lead to expression variance of AP-1 both in mRNA and protein level. In BmN cells, both the heavy chain γ and light chain σ could clearly co-localize with AP-1 ß, mostly forming pits in cytoplasm. Two isoforms of AP-1 σ corresponded to distinct subcellular distribution pattern, possibly due to C-terminal amino acids difference.

Phenol oxidase is a necessary enzyme for the silkworm molting which is regulated by molting hormone.

Insect molting is an important developmental process of metamorphosis, which is initiated by molting hormone. The molting process includes the activation of dermal cells, epidermal cells separation, molting fluid secretion, the formation of new epidermis and old epidermis excoriation etc. Polyphenol oxidases (PPOs), dopa decarboxylase and acetyltransferase are necessary enzymes for this process. Traditionally, the phenol oxidase was considered as an enzyme for epidermal layer's tanning and melanization. This work suggested that polyphenol oxidases are one set of the key enzymes in molting, which closely related with the role of ecdysone in regulation of molting processes. The data showed that the expression peak of phenol oxidase in silkworm is higher during molting stage, and decreases after molting. The significant increase in the ecdysone levels of haemolymph was observed in the artificially fed silkworm larvae with ecdysone hormone. Consistently, the phenol oxidase expression was significantly elevated compared to the control. PPO1 RNAi induced phenol oxidase expression obviously declined in the silkworm larvae, and caused the pupae incomplete pupation. Overall, the results described that the phenol oxidase expression is regulated by the molting hormone, and is a necessary enzyme for the silkworm molting.

Expression and localization of silkworm adaptor protein complex-1 subunits, which were down-regulated post baculovirus infection.

Adaptor protein complexes (APs) function as vesicle coat components in different membrane traffic pathways. In this study the subunits of adaptor protein complex-1 (AP-1) of silkworm Bombyx mori were molecularly characterized. All coding genes for the four subunits were cloned and sequenced. Phylogenic tree for each adaptin was constructed and all subunits were found to be conserved in respective group among organisms. The mRNA expression pattern for each adaptin was similar among tissues. Alternative splicing event was observed in genes encoding both the heavy chain gamma and beta adaptin and the light chain subunit, which could generate other possible adaptin forms. GFP-tagged fusion proteins indicated that AP-1 located in the peripheral plasma area. Furthermore, the BmNPV infection in B. mori cells had differentiated effect on the expression level of AP-1 subunits.

A transgenic Bm cell line of piggyBac transposon-derived targeting expression of humanized glycoproteins through N-glycosylation.

Glycoproteins have been implicated in a wide variety of important biochemical and biological functions, including protein stability, immune function, enzymatic function, cellular adhesion and others. Unfortunately, there is no therapeutic protein produced in insect system to date, due to the expressed glycoproteins are paucimannosidic N-glycans, rather than the complex, terminally sialylated N-glycans in mammalian cells. In this paper, we cloned the necessary genes in glycosylation of mammalian cells, such as N-acetylglucosaminyltransferase II (Gn-TII), galactosyltransferases (Gal-Ts), 2,6-Sial-T (ST6 GalII)and 2,3-Sial-T (ST3GalIII), and transformed them to silkworm genome of BmN cell line through transgenesis to establish a transgenic Bm cell line of piggyBac transposon-derived targeting expression of humanized glycoproteins. The study supplied a new insect cell line which is practically to produce "bisected" complex N-glycans like in mammalian cells.

A transgenic Marc-145 cell line of piggyBac transposon-derived targeting shRNA interference against porcine reproductive and respiratory syndrome virus.

Porcine reproductive and respiratory syndrome (PRRS) is now considered to be one of the most important diseases in countries with intensive swine industries. The two major membrane-associated proteins of porcine reproductive and respiratory syndrome virus (PRRSV), GP5 and M (encoded by ORF5 and ORF6 genes, respectively), are associated as disulfide-linked heterodimers (GP5/M) in the virus particle. In this study, we designed 5 of the small hairpin RNAs (shRNAs) targeting the GP5 and M gene of PRRSV respectively, and investigated their inhibition to the production of PRRSV. The highest activity displayed in shRNAs of the ORF6e sequence (nts 261-279), which the inhibition rate reached was 99.09%. The result suggests that RNAi technology might serve as a potential molecular strategy for PRRSV therapy. Furthermore, the transgenic Marc-145 cell line of piggyBac transposon-derived targeting shRNA interference against PRRS virus was established. It presented stable inhibition to the replication and amplification of PRRS. The work implied that shRNAs targeting the GP5 and M gene of PRRSV may be used as potential RNA vaccines in vivo, and supplied the screening methods of transformed pig embryonic fibroblast which are prerequisite for the disease-resistant transgenic pigs to PRRS.

Silkworms transformed with chimeric silkworm/spider silk genes spin composite silk fibers with improved mechanical properties.

The development of a spider silk-manufacturing process is of great interest. However, there are serious problems with natural manufacturing through spider farming, and standard recombinant protein production platforms have provided limited progress due to their inability to assemble spider silk proteins into fibers. Thus, we used piggyBac vectors to create transgenic silkworms encoding chimeric silkworm/spider silk proteins. The silk fibers produced by these animals were composite materials that included chimeric silkworm/spider silk proteins integrated in an extremely stable manner. Furthermore, these composite fibers were, on average, tougher than the parental silkworm silk fibers and as tough as native dragline spider silk fibers. These results demonstrate that silkworms can be engineered to manufacture composite silk fibers containing stably integrated spider silk protein sequences, which significantly improve the overall mechanical properties of the parental silkworm silk fibers.

Molecular cloning and characterization of a putative cDNA encoding endoglucanase IV from Trichoderma viride and its expression in Bombyx mori.

The development of cellulase production technology has greatly contributed to the successful use of cellulosic materials as renewable carbon sources. In this study, a putative endoglucanase IV (EG IV) complementary DNA was cloned from the mycelium of a strain of the filamentous fungus Trichoderma viride using a PCR-based exon-splicing method and expressed in both a silkworm BmN cell line and in silkworm larvae. Western blot analysis detected a band of 42 kDa in BmN cells after infection with a recombinant mBacmid/BmNPV/EG IV baculovirus. Sequence alignment analysis of the T. viride EG IV gene showed two domains that were highly conserved with glycosyl hydrolases and a funga-type cellulose-binding domain. Analysis of variance showed that silkworms infected with recombinant baculoviruses exhibited significantly higher enzyme activity that was 48.84% higher than silkworms infected with blank baculoviruses and 46.61% higher than normal silkworms. The expressed bioactive EG IV was also stable at the pH range from 5.0 to 10.0. The availability of large quantities of bioactive EG IV in silkworm provided a possibility to produce cellulase transgenic silkworm, which express bioactive cellulase specially in its digestive tract and improve its metabolism efficiency of mulberry leaves. Its application in the sericulture industry may be very promising.

Heterologous expression characteristics of Trichoderma viride endoglucanase V in the silkworm, Bombyx mori L.

Efficient degradation of cellulose needs a synergistic reaction of the cellulolytic enzymes, which include exoglucanases, endoglucanases, and ß-1,4-glucosidase. In this study, we used an improved Bac-to-Bac/BmNPV baculovirus expression system, which lacks the virus-encoded chitinase cathepsin (v-cath) genes of Bombyx mori nucleopolyhedrovirus (BmNPV), to express the endoglucanase V (EG V) gene from Trichoderma viride in silkworm BmN cells and silkworm larvae, and analyzed the characteristics of the recombinant enzyme in silkworm larvae. The result showed that an around 36-kDa protein was visualized in BmN cells at 48 h after the second-generation recombinant mBacmid/BmNPV/EG V baculovirus infection. The crude enzyme extract from the recombinant baculoviruses-infected silkworms exhibited a significant maximum activity at the environmental condition of pH 5.0 and a temperature of 50 °C, and increased 39.86% and 37.76% compared with that from blank mBacmid/BmNPV baculovirus-infected silkworms and normal silkworms, respectively. It was stable at pH range from 5.0 to 10.0 and at temperature range from 40 to 60 °C. The availability of large quantities of EG V that the silkworm provides might greatly facilitate the future research and the potential application in industries.

Cloning and characterization of the Bombyx mori ecdysone oxidase.

The physiological titer of molting hormones in insects depends on relative activities of synthesis and degradation pathways. Ecdysone oxidase (EO) is a key enzyme in the inactivation of ecdysteroid. However, there are only a few reports on ecdysteroid inactivation and its enzymes in silkworm. In this study, we cloned and characterized the Bombyx mori EO (BmEO). The BmEO cDNA contains an ORF of 1,695 bp and the deduced protein sequence contains 564 amino acid residues. The deduced protein sequence contains two functional domains of glucose-methanol-choline oxidoreductase in N-terminal and C-terminal. Comparing the expression levels of BmEO in different tissues, high transcription was mainly present in hemocytes. Reduced expression of this enzyme is expected to lead to pathological accumulation of ecdysone in the hemolymph of silkworm larvae or pupae. Our data show that RNA inference of BmEO transcripts resulted in the accumulation of ecdysteroid and death of larvae or pupae. We infer that EO is a crucial element in the physiology of insect development.