MicroRNA bmo-miR-31-5p inhibits apoptosis and promotes BmNPV proliferation by targeting the CYP9e2 gene of Bombyx mori

BACKGROUND

Bombyx mori nuclear polyhedrosis virus (BmNPV), as a typical baculovirus, is the primary pathogen that infects the silkworm B. mori, a lepidopteran species. Owing to the high biological safety of BmNPV in infecting insects, it is commonly utilized as a biological insecticide for pest control. Apoptosis is important in the interaction between the host and pathogenic microorganisms. MicroRNAs (miRNAs) influence immune responses and promote stability of the immune system via apoptosis. Therefore, the study of apoptosis-related miRNA in silkworms during virus infection can not only provide support for standardizing the prevention and control of diseases and insect pests, but also reduce the economic losses to sericulture caused by the misuse of biological pesticides.

RESULTS

Through transcriptome sequencing, we identified a miRNA, miR-31-5p, and demonstrated that it can inhibit apoptosis in silkworm cells and promote the proliferation of BmNPV in BmE-SWU1 cells. We identified a target gene of miR-31-5p, B. mori cytochrome P450 9e2 (BmCYP9e2), and demonstrated that it can promote apoptosis in silkworm cells and inhibit the proliferation of BmNPV. Moreover, we constructed transgenic silkworm strains with miR-31-5p knockout and confirmed that they can inhibit the proliferation of BmNPV.

CONCLUSION

These data indicate that miR-31-5p may exert functions of inhibiting apoptosis and promoting virus proliferation by regulating BmCYP9e2. The findings demonstrate how miRNAs influence host cell apoptosis and how they are involved in the host immune system response to viruses, providing important insights into the applications of biological insecticides for pest control. © 2024 Society of Chemical Industry.

Bombyx moriSuppressor of Hairless is involved in the regulation of the silkworm cell cycle and endoreplication of the silk glands

The Notch signaling pathway is important in cell cycle regulation and cell proliferation. The transcriptional repressor Suppressor of Hairless [Su(H)] is a molecular switch for downstream target genes of the Notch signaling pathway but the regulatory mechanism of the Su(H) gene in the cell cycle is unclear. We determined the function of the Notch signaling pathway and Bombyx mori Su(H) [BmSu(H)] in the regulation of the silkworm cell cycle. Inhibition of Notch signaling promoted the replication of DNA in silkworm gland cells and expression of the BmSu(H) gene was significantly reduced. Overexpression of the BmSu(H) gene inhibited DNA replication and cell proliferation of silkworm cells, whereas knockout of the BmSu(H) gene promoted DNA replication and cell proliferation. Knockout of the BmSu(H) in silkworms improved the efficiency of silk gland cell endoreplication and increased important economic traits. We demonstrated that BmSu(H) protein can directly bind to the promoters of BmCyclinA, BmCyclinE and BmCDK1 genes, inhibiting or promoting their transcription at the cell and individual level. This study identified molecular targets for genetic improvement of the silkworm and also provided insights into the regulatory mechanism of the cell cycle.

BmNPV Bm60 is a key target gene used by a resistant strain of Bombyx mori to inhibit BmNPV proliferation

Bombyx mori nucleopolyhedrovirus (BmNPV) is a pathogen that causes significant losses to the silkworm industry. Numerous antiviral genes and proteins have been identified by studying silkworm resistance to BmNPV. However, the molecular mechanism of silkworm resistance to BmNPV is unclear. We analyzed the differences between the susceptible strain 871 and a near-isogenic resistant strain 871C. The survival of strain 871C was significantly greater than that of 871 after oral and subcutaneous exposure to BmNPV. Strain 871C exhibited a nearly 10,000-fold higher LD50 for BmNPV compared to 871. BmNPV proliferation was significantly inhibited in all tested tissues of strain 871C using HE strain and fluorescence analysis. Strain 871C exhibited cellular resistance to BmNPV rather than peritrophic membrane or serum resistance. Strain 871C suppressed the expression of the viral early gene Bm60. This led to the inhibition of BmNPV DNA replication and late structural gene transcription based on the cascade regulation of baculovirus gene expression. Bm60 could also interact with the viral DNA binding protein and alkaline nuclease, as well as host proteins Methylcrotonoyl-CoA carboxylase subunit alpha, mucin-2-like protein, and 30 K-8. Overexpression of 30 K-8 significantly inhibited BmNPV proliferation. These results increase understanding of the molecular mechanism behind silkworm resistance to BmNPV and suggest targets for the breeding of resistant silkworm strains and the controlling pest of Lepidoptera.

[Ewing's sarcoma of central nervous system: a clinicopathological analysis of six cases]

Objective: To investigate the clinicopathological characteristics, pathological diagnosis of Ewing's sarcoma of the central nervous system. Methods: Six cases of Ewing's sarcoma of the central nervous system diagnosed at the First Affiliated Hospital of Nanjing Medical University, Nanjing, China from 2015 to 2022 were collected. The clinical manifestations, histological morphology, immunophenotype and molecular genetics of these cases were analyzed. The related literature was reviewed. Results: There were four males and two females, with a male to female ratio of 2∶1. The onset age was 17-40 years, with a median age of 23 years. All 6 tumors were located in the spinal cord (2 cases of cervical vertebra, 1 case of thoracic vertebra, 2 cases of lumbar vertebra, and 1 case of sacral vertebra). The patients' clinical manifestations were mostly lumbago, weakness and numbness of lower limbs/limbs. In 1 case, the tumor recurred and metastasized to the suprasellar region and the third ventricle. Microscopically, the tumor showed diffuse infiltrative growth. In some cases, the tumor was closely related to the spinal meninges. The tumor cells were arranged in sheet, lobular, thin-rope, and nest-like patterns. Homer-Wright rosette was visible. The tumor cells were small to medium in size, and most of them had scant cytoplasm. A few cells had clear cytoplasm. Some areas were rhabdoid. The tumor cell nuclei showed focal mild pleomorphism. The chromatin was uniform and delicate while the nucleoli were not obvious. Mitosis was commonly seen. The tumor was separated by fibrous connective tissue and may be accompanied by mucinous degeneration. Immunohistochemistry showed that all tumors were positive for CD99, NKX2.2, Fli1, ERG. ATRX, H3K27me3, INI1 and BRG1 were all retained. Immunohistochemical stains for EMA, GFAP and Olig2 were negative. The Ki-67 proliferation index was 30%-70%. EWSR1 break-apart FISH test was positive. Conclusions: Ewing's sarcoma is rare in the central nervous system and needs to be distinguished from a variety of neoplasms with primitive undifferentiated small cell morphology. Immunohistochemistry and molecular genetics may be required for a proper diagnosis.

Matrix metalloproteinase 2 degrades collagen I to regulate ovarian development by association with an insulin-like peptide

The ovary generally undergoes tissue remodeling during larval to pupal transition, which includes membrane degeneration and ovariole growth. At the same time, the hormones produced by insects significantly change during metamorphosis. However, the regulatory mechanism for ovarian development and hormones is not fully understood in insects. Herein, we found that matrix metalloproteinase 2 (MMP2) was highly expressed in the ovarian capsules and ovarioles, and the development was abnormal after knocking out MMP2 in Bombyx mori. The process of abnormal degradation of collagen I due to MMP2 deletion, which resulted in abnormal development of ovarioles and eggs, was analyzed in detail. The proteomics of ovaries in the MMP2-knock out and wild type strains showed a critically significant difference in the expression of a protein, insulin-like peptide (ILP). Additional analysis revealed significant alteration of ILP during ovarian development, and abnormal expression of ILP significantly affected ovarian development in vivo and MMP2 expression in vitro and in vivo. These results showed that MMP2 regulation of ovarian tissue remodeling is closely related to ILP expression. Our study provides new insights into the regulatory mechanism of MMP2 and ovarian development in B. mori.

[CIC-rearranged sarcoma: a clinicopathological analysis of four cases]

Objective: To investigate the clinicopathological features and differential diagnosis of CIC-rearranged sarcoma (CRS). Methods: Five CRSs of 4 patients (2 biopsies of pelvic cavity and lung metastasis from case 4) diagnosed in the First Affiliated Hospital of Nanjing Medical University were enrolled from 2019 to 2021. All cases were evaluated by clinical presentation, H&E, immunohistochemical staining and molecular analysis and the related literature was reviewed. Results: There were one male and three females, the age at diagnosis ranged from 18 to 58 (mean 42.5) years. Three cases were from the deep soft tissues of the trunk and one case from the skin of foot. Grossly, the tumor size ranged from 1 to 16 cm. Microscopically, the tumor was arranged in nodules or solid sheets. The tumor cells were typically round or ovoid, with occasional spindled or epithelioid morphology. The nuclei were round to ovoid with vesicular chromatin and prominent nucleoli. Mitotic figures were brisk (>10/10 HPF). Rhabdoid cells were seen in four of five cases. Myxoid change and hemorrhage were observed in all samples and two cases showed geographic necrosis. Immunohistochemically, CD99 was variably positive in all samples, while WT1 and TLE-1 were positive in four of five samples. Molecular analysis showed CIC-rearrangements in all cases. Two patients succumbed within 3 months. One had mediastinal metastasis 9 months after surgery. One underwent adjuvant chemotherapy and remained tumor-free 10 months after diagnosis. Conclusions: CIC-rearranged sarcoma is uncommon and shows aggressive clinical course with dismal prognosis. The morphological and immunohistochemical characteristics can largely overlap with a variety of sarcomas; hence, knowledge of this entity is vital to avoid potential diagnostic pitfalls. Definitive diagnosis requires molecular confirmation of CIC-gene rearrangement.

A novel transcription factor, BmZFP67, regulates endomitosis switch by controlling the expression of cyclin B in silk glands

Endomitosis is involved in developmental processes associated with an increase in metabolic cell activity, which is characterized by repeated rounds of DNA replication without cytokinesis. Endomitosis cells are widespread in protozoa, plants, animals and humans. Endomitosis cell cycle is currently viewed as a variation of the canonical cell cycle and transformed from mitotic cell cycle. However, the meaningful question about how endomitosis transformed from mitosis is still unclear. Herein, we identified a novel transcription factor in silk glands, ZFP67, which is gradually reduced in silk glands during the transition of mitosis to endomitosis. In addition, over-expressed ZFP67 in silk glands led to the transition delayed. And, knock-out of ZFP67 led to abnormal chromatin division and unsuccessful cell division. These data reveled that ZFP67 played an important role in transition of mitosis to endomitosis. Furthermore, ZFP67 can regulate the transcription of cyclin B, a key cyclin related to cell division and G2/M phase, which is demonstrated by chromatin immunoprecipitation and dual luciferase reporter system in this article. In conclusion, it can be speculated that the decreasing expression of ZFP67 in silk glands during the transition stage of mitosis-to-endomitosis resulted in the lack of cyclin B, which further led to unsuccessful cytokinesis and then promoted the transition from mitosis to endomitosis of silk gland cells.

[Diffuse midline glioma with H3K27 alteration in adults: a clinicopathological analysis]

Objective: To investigate the clinicopathological characteristics, pathological diagnosis and prognosis of diffuse midline glioma (DMG) with H3K27 alteration in adults. Methods: Twenty cases of H3K27-altered adult DMG diagnosed in the First Affiliated Hospital of Nanjing Medical University were enrolled from 2017 to 2022. All cases were evaluated by clinical and imaging presentations, HE, immunohistochemical staining and molecular genetics; and the relevant literature was reviewed. Results: The ratio of male to female was 1∶1, and the median age was 53 years (range from 25 to 74 years); the tumors were located in the brainstem (3/20, 15%) and non-brainstem (17/20, 85%; three in thoracolumbar spinal cord and one in pineal region). The clinical manifestations were non-specific, mostly dizziness, headache, blurred vision, memory loss, low back pain, limb sensation and/or movement disorders, etc. Microscopically, the tumors showed infiltrative growth, with WHO grade 2 (3 cases), grade 3 (12 cases), and grade 4 (5 cases). The tumors showed astrocytoma-like and oligdendroglioma-like, pilocytic astrocytoma-like and epithelioid-like patterns. Immunohistochemically, the tumor cells were positive for GFAP, Olig2 and H3K27M, and H3K27me3 expression was variably lost. ATRX expression was lost in four cases, p53 was strongly positive in 11 cases. Ki-67 index was about 5%-70%. Molecular genetics showed p. k27m mutation in exon 1 of H3F3A gene in 20 cases; BRAF mutation in two cases: V600E and L597Q mutation in one case each. Follow up intervals ranged from 1 to 58 months, and the survival time for brainstem (6.0 months) and non-brainstem (30.4 months) tumors was significantly different (P<0.05). Conclusions: DMG with H3K27 alteration is uncommonly found in adults, mostly occurs in non-brainstem, and can present in adults of all ages. Owing to the wide histomorphologic features, mainly astrocytic differentiation, routine detection of H3K27me3 in midline glioma is recommended. Molecular testing should be performed on any suspected cases to avoid missed diagnosis. Concomitant BRAF L597Q mutation and PPM1D mutation are novel findings. The overall prognosis of this tumor is poor, with tumors located in the brainstem showing worse outcome.

Apoptosis-related long non-coding RNA LINC5438 of Bombyx mori promotes the proliferation of BmNPV

Apoptosis, as an important part of the immune response, is one of the core events in the host-virus interaction. Studies have shown that long non-coding RNAs (lncRNAs) play important roles in the process of cell apoptosis and pathophysiology. To investigate the apoptosis-related lncRNAs involved in Bombyx mori nucleopolyhedrovirus (BmNPV) infecting silkworms, transcriptome sequencing was conducted based on silkworm cells infected with BmNPV before and after B. mori inhibitor of apoptosis (Bmiap) gene knockout. A total of 23 differentially expressed lncRNAs were identified as being associated with the mitochondrial apoptosis pathway. Moreover, we demonstrated that B. mori LINC5438 has the function of inhibiting apoptosis in silkworm cells. Overexpression of LINC5438 promoted the proliferation of BmNPV, while interference with LINC5438 inhibited its proliferation, indicating that LINC5438 plays an important role in BmNPV infection. Our results also showed that LINC5438 can regulate the expression of Bmiap, BmDronc, BmICE, and its predicted target gene BmAIF, suggesting that LINC5438 may function through the mitochondrial pathway. These findings provide important insights into the mechanisms of virus-host interaction and the applications of baculoviruses as biological insecticides.

Identification of the Key Functional Domains of Bombyx mori Nucleopolyhedrovirus IE1 Protein

The immediate early protein 1 (IE1) acts as a transcriptional activator and is essential for viral gene transcription and viral DNA replication. However, the key regulatory domains of IE1 remain poorly understood. Here, we analyzed the sequence characteristics of Bombyx mori nucleopolyhedrovirus (BmNPV) IE1 and identified the key functional domains of BmNPV IE1 by stepwise truncation. Our results showed that BmNPV IE1 was highly similar to Autographa californica nucleopolyhedrovirus (AcMNPV) IE1, but was less conserved with IE1 of other baculoviruses, the C-terminus of IE1 was more conserved than the N-terminus, and BmNPV IE1 was also necessary for BmNPV proliferation. Moreover, we found that IE1_158–208 was a major nuclear localization element, and IE1_1–157 and IE1_539–559 were minor nuclear localization elements, but the combination of these two minor elements was equally sufficient to fully mediate the nuclear entry of IE1. Meanwhile, IE1_1–258, IE1_560–584, and the association of amino acids 258 and 259 were indispensable for the transactivation activity of BmNPV IE1. These results systematically resolve the functional domains of BmNPV IE1, which contribute to the understanding of the mechanism of baculovirus infection and provide a possibility to synthesize a small molecule IE1-truncated mutant as an agonist or antagonist.

E2F4 regulates the cell cycle and DNA replication in the silkworm, Bombyx mori

The E2F family of transcription factors is crucial for cell cycle progression and cell fate decisions. Although E2Fs have been widely studied in mammals, there have been few studies performed in insects. Here, we determined the function of E2F4 in the silkworm, Bombyx mori. We demonstrate that E2F proteins are highly conserved among species from lower animals to higher mammals. Overexpression of the BmE2F4 gene led to cell cycle arrest in the G1 phase, whereas interfering with the BmE2F4 mRNA led to accumulation of cells in the S phase. These results indicate that BmE2F4 is important in cell cycle regulation. We also demonstrate that the BmE2F4 gene is involved in DNA replication of BmN-SWU1 cells and DNA synthesis in the silk gland. Furthermore, we identified a protein called Bm14-3-3ζ that can interact with BmE2F4 and allow it to localize in the nucleus. Overexpression of the Bm14-3-3ζ gene led to cell cycle arrest in the G1 phase, while knocking down the gene increased the proportion of cells in S phase. These findings provide important insights into the function of E2F transcription factors and increase our understanding of their involvement in cell cycle regulation.

[Clinicopathological features of polymorphous low-grade neuroepithelial tumor of the young]

Objective: To investigate the clinicopathological features and differential diagnosis of polymorphous low-grade neuroepithelial tumor of the young (PLNTY). Methods: Five cases of PLNTY diagnosed at the First Affiliated Hospital and Affiliated Brain Hospital of Nanjing Medical University, Nanjing, China from 2019 to 2021 were collected. All cases were evaluated using clinical and imaging data, histology, immunohistochemical staining and molecular genetics. The relevant literature was reviewed. Results: There were two male and three female patients, aged 10 to 39 years, with an average age of 25 years. Clinically, the tumors were in the temporal lobe (3 cases), the lateral ventricle (1 case) and the left head of caudate nucleus (1 case). The clinical manifestations included epilepsy in 3 cases, right visual disturbance in 1 case, and post-trauma incidental finding in 1 case. Microscopically, the lesions were characterized with infiltrative growth, cellular pleomorphism (oligodendroglioma-like cells were always present, with low-grade, pleomorphic nuclei) and variable calcifications. Immunohistochemically, the tumor cells were positive for GFAP and Olig2. They also showed intense and diffuse expression of CD34 while CD34 expressing ramified neural elements were present in regional cortex. Ki-67 proliferation index was less than 3%. Molecular genetics showed the BRAF V600E mutation in 2 cases, the PAK5-Q337R missense mutation in 1 case, the FGFR2-CTNNA3 fusion in 1 case, and the FGFR2-INA and FGFR2-PPRC1 concomitant fusion in 1 case. No postoperative chemoradiotherapy was given. Follow-up intervals ranged from 3 to 29 months while no recurrence or metastasis was identified. Conclusions: PLNTY is uncommon. A definite diagnosis of PLNTY relies on histopathological examination and molecular genetics. It is important to distinguish PLNTY from high grade gliomas and avoid overtreatment. The recently reported the PAK5-Q337R missense mutation and the FGFR2-PPRC1 gene fusion in PLNTY may help diagnose and understand the pathogenesis of PLNTY.

[Clinicopathological features of clear cell carcinoma of salivary gland in the head and neck]

Objective: To investigate the clinical, histologic, immunohistochemical (IHC) and molecular genetic features of clear cell carcinoma (CCC) of salivary gland in the head and neck regions. Methods: Seven cases of CCC diagnosed in the Department of Pathology, the First Affiliated Hospital of Nanjing Medical University from 2018 to 2021 were included. The clinical and pathologic data, HE sections and IHC staining were reviewed, and EWSR1 gene translocation was detected by fluorescence in situ hybridization (FISH). The relevant literature was also reviewed. Results: There were five males and two females, with an age range of 32 to 71 years (mean 50 years). The tumors were located in the palate, base of tongue, subglottic, right submaxillary and nasopharynx. Histologically the tumors were composed of sheets, nests, and trabecular of large, monomorphic cells which possessed abundant clear and eosinophilic cytoplasm. The stroma was characterized by abundant hyalinized fibrous strands admixed with cellular fibrous (desmoplastic) tissue. The tumor growth was infiltrative. IHC staining revealed positivity for CKpan and squamous cell immunophenotypic markers (CK5/6, p63 and p40), but negativity for myoepithelial markers (SMA, calponin, GFAP and CD10). The EWSR1 gene translocation was detected by FISH. The prognosis was excellent, with the follow-up periods ranging from 8 months to 33 months. During this period, six patients survived without tumor, only one patient with cervical lymph node metastasis. Conclusions: CCC of salivary gland is rare and needs to be differentiated from various other types of tumors containing clear cells. Awareness of the histopathologic characteristics, and combined with IHC and molecular genetic examination can avoid misdiagnosis. The biological behavior of the tumor is indolent with a good overall prognosis.

[Clinicopathological features of ectopic meningothelial hamartoma]

Objective: To investigate the clinicopathological features, diagnosis and differential diagnosis of ectopic meningothelial hamartoma (EMH). Methods: Three cases of EMH diagnosed in the First Affiliated Hospital of Nanjing Medical University from January 2014 to December 2020 were enrolled. All cases were evaluated by clinical and imaging features, HE and immunohistochemical staining, and the relevant literature was reviewed. Results: There were one male and two female patients, aged 2, 67 and 19 years, respectively. Clinically, they presented as skin masses in the head and face region (two cases) and sacro-coccygeal region (one case). Grossly, the lesions ranged in size from 1.6 cm to 8.9 cm. Microscopically, the lesions were ill-defined, and located in the dermis and subcutis, and showed pseudovascular channels lined by monolayer of cuboidal to flattened epithelium with mild atypia, with variable cystic cavity formation. There was prominent interstitial fibrosis. Concentric, lamellated, onion skin-like arrangement with short spindle or ovoid cells and psammoma bodies were noted. Immunohistochemically, these cells were strongly positive for SSTR2, EMA, vimentin and progesterone receptor. Ki-67 positive index was low, approximately 1%. Conclusions: EMH is uncommon. Definitive diagnosis relies on histopathologic examination. The importance in recognizing the lesions is to differentiate from other more aggressive tumors.

Geminin is essential for DNA re-replication in the silk gland cells of silkworms

Endoreplication, known as endocycles or endoreduplication, is a cell cycle variant in which the genomic DNA is re-replicated without mitosis leading to polyploidy. Endoreplication is essential for the development and functioning of the different organs in animals and plants. Deletion of Geminin, a DNA replication licensing inhibitor, causes DNA re-replication or damage. However, the role of Geminin in endoreplication is still unclear. Here, we studied the role of Geminin in the endoreplication of the silk gland cells of silkworms by constructing two transgenic silkworm strains, including BmGeminin1-overexpression and BmGeminin1-RNA interference. Interference of BmGeminin1 led to body weight gain, increased silk gland volume, increased DNA content, and enhanced DNA re-replication activity relative to wild-type Dazao. Meanwhile, overexpression of BmGeminin1 showed an opposite phenotype compared to the BmGem1-RNAi strain. Furthermore, RNA-sequencing of the transgenic strains was carried out to explore how BmGeminin1 regulates DNA re-replication. Our data demonstrated a vital role of Geminin in the regulation of endoreplication in the silk gland of silkworms.

Bombyx mori Nucleopolyhedrovirus (BmNPV) Induces G2/M Arrest to Promote Viral Multiplication by Depleting BmCDK1

Simple Summary

Baculoviruses arrest the cell cycle in the S or G2/M phase in insect cells, but the exact mechanism of this process still remains obscure. Bombyx mori nucleopolyhedrovirus (BmNPV), one of the best characterized baculoviruses, is an important pathogen in silkworms. In the present study, we determined that downregulation of BmCDK1 and BmCyclin B expression was required for BmNPV-mediated G2/M phase arrest, which plays an essential role in facilitating BmNPV replication. Further investigations showed that BmNPV IAP1 interacted with BmCDK1. The overexpression of the BmNPV iap1 gene led to the accumulation of cells in the G2/M phase, and BmNPV iap1 gene knockdown attenuated the effect of BmNPV-mediated G2/M phase arrest. These findings enhance the understanding of BmNPV pathogenesis, and indicate a novel mechanism through which baculoviruses impact the cell cycle progression.

Abstract

Understanding virus–host interaction is very important for delineating the mechanism involved in viral replication and host resistance. Baculovirus, an insect virus, can cause S or G2/M phase arrest in insect cells. However, the roles and mechanism of Baculovirus-mediated S or G2/M phase arrest are not fully understood. Our results, obtained using flow cytometry (FCM), tubulin-labeling, BrdU-labeling, and CellTiter 96^® AQueous One Solution Cell Proliferation Assay (MTS), showed that Bombyx mori nucleopolyhedrovirus (BmNPV) induced G2/M phase arrest and inhibited cellular DNA replication as well as cell proliferation in BmN-SWU1 cells. We found that BmNPV induced G2/M arrest to support its replication and proliferation by reducing the expression of BmCDK1 and BmCyclin B. Co-immunoprecipitation assays confirmed that BmNPV IAP1 interacted with BmCDK1. BmNPV iap1 was involved in the process of BmNPV-induced G2/M arrest by reducing the content of BmCDK1. Taken together, our results improve the understanding of the virus–host interaction network, and provide a potential target gene that connects apoptosis and the cell cycle.

The dual roles of three MMPs and TIMP in innate immunity and metamorphosis in the silkworm, Bombyx mori

The matrix metalloproteinases (MMPs) and their endogenous inhibitory factors, tissue inhibitors of metalloproteinases (TIMPs), are implicated in many diseases. However, the mammalian MMPs (> 20) and TIMPs (> 3) are larger in number, and so little is known about their individual roles in organisms. Hence, we have systematically studied the roles of all three MMPs and one TIMP in silkworm innate immunity and metamorphosis. We observed that MMPs and TIMP are highly expressed during the pupation stage of the silkworms, and TIMP could interact with each MMPs. High-activity MMPs and low-activity TIMP may enhance the infection of B. mori nucleopolyhedrovirus in both in vitro and in vivo. MMPs' knockout and TIMP overexpression delayed silkworm development and even caused death. Interestingly, different MMPs' knockout led to different tubular tissue dysplasia. These findings provide insights into the conserved functions of MMPs and TIMP in human organogenesis and immunoregulation.

Bombyx mori cell division cycle protein 37 promotes the proliferation of BmNPV

Cell division cycle protein 37 (Cdc37) is a molecular chaperone that actively participates in many intracellular physiological and biochemical processes as well as pathogen infection. However, the function of Cdc37 in silkworm cells under Bombyx mori nucleopolyhedrovirus (BmNPV) infection is unknown. We cloned and identified BmCdc37, a Cdc37 gene from B. mori, which is highly conserved among other species. After BmNPV infection, the expression level of the BmCdc37 gene was up-regulated and showed an expression pattern similar to the BmHsp90 gene, which relies on Cdc37 to stabilize and activate specific protein kinases. The immunofluorescence, bimolecular fluorescence complementation (BiFC), and co-immunoprecipitation (Co-IP) assays all indicated that BmCdc37 interacts with BmHsp90 in silkworm cells. Both BmCdc37 and BmHsp90 promote the reproduction of BmNPV. Co-expression of BmCdc37 and BmHsp90 was better at promoting virus proliferation than overexpression alone. These findings all indicate that BmCdc37 plays an active role in the proliferation of BmNPV.

Transcriptome analysis reveals changes in silkworm energy metabolism during Nosema bombycis infection

Energy metabolism is important for the proliferation of microsporidia in infected host cells, but there is limited information on the host response. The energy metabolism response of silkworm (Bombyx mori) to microsporidia may help manage Nosema bombycis infections. We analyzed differentially expressed genes in the B.mori midgut transcriptome at two significant time points of microsporidia infection. A total of 1448 genes were up-regulated, while 315 genes were down-regulated. A high proportion of genes were involved in the phosphatidylinositol signaling system, protein processing in the endoplasmic reticulum, and glycerolipid metabolism at 48 h post infection (h p.i.), and a large number of genes were involved in the TCA cycle and protein processing at 120 h p.i. These results showed that the early stages of microsporidia infection affected the basic metabolism and biosynthesis processes of the silkworm. Knockout of Bm_nscaf2860_46 (Bombyx mori isocitrate dehydrogenase, BmIDH) and Bm_nscaf3027_062 (Bombyx mori hexokinase, BmHXK) reduced the production of ATP and inhibited microsporidia proliferation. Host fatty acid degradation, glycerol metabolism, glycolysis pathway, and TCA cycle response to microsporidia infection were also analyzed, and their importance to microsporidia proliferation was verified. These results increase our understanding of the molecular mechanisms involved in N. bombycis infection and provide new insights for research on microsporidia control. IMPORTANCE: Nosema bombycis can be vertically transmitted in silkworm eggs. The traditional prevention and control strategies for microsporidia are difficult and time-consuming, and this is a problem in silkworm culture. Research has mainly focused on host gene functions related to microsporidia infection and host immune responses after microsporidia infection. Little is known about the metabolic changes occurring in the host after infection. Understanding the metabolic changes in the silkworm host could aid in the recognition of host genes important for microsporidia infection and growth. We analyzed host metabolic changes and the main participating pathways at two time points after microsporidia infection and screened the microsporidia-dependent host energy metabolism genes BmIDH and BmHXK. The results revealed genes that are important for the proliferation of Nosema bombycis. These results illustrate how microsporidia hijack the host genome for their growth and reproduction.

Comparative genome-wide DNA methylation analysis reveals epigenomic differences in response to heat-humidity stress in Bombyx mori

DNA methylation is an important epigenetic modification and has been shown to be involved in the response to abiotic stress. However, there are few studies on DNA methylation in insect response to environmental signals. In this study, we conducted a comprehensive comparative analysis of DNA methylation profiles between two silkworm strains with significantly different resistance to heat and humidity by whole-genome bisulfite sequencing (WGBS). We identified, in total, 2934 differentially methylated regions (DMRs) between RT_48h (resistant strain with high-temperature/humidity treatment for 48 h) and ST_48h (sensitive strain with high-temperature/humidity treatment for 48 h) under cytosine context (CG), which corresponded to 1230 DMR-related genes (DMGs), and the DMRs were primarily located in the gene body (exon and intron) region. Gene ontology (GO) and KEGG analysis showed that these DMGs were most significantly enriched in binding, cellular metabolic process, and RNA transport pathways. Moreover, 10 DMGs have been revealed to be involved in the heat-humidity stress response in the silkworm. The results of this study indicated that DNA methylation plays crucial roles in silkworm response to environmental stressors and provides important clues to identify key resistance genes in silkworm under high-temperature/humidity stress response.

Gene editing the BmNPV inhibitor of apoptosis protein 2 (iap2) as an antiviral strategy in transgenic silkworm

Apoptosis is a cellular defense mechanism used for the elimination of host cells infected by viruses. Viruses have evolved corresponding inhibitors of apoptosis genes to promote their replication. Anti-apoptosis-related genes, involved in baculovirus proliferation, have been proposed but it is unclear whether these genes can be manipulated in gene therapy. We constructed a transgenic silkworm, using the CRISPR/Cas9 system to knock out the BmNPV inhibitor of apoptosis 2 (iap2). The sequencing results showed that all the sequences could edit the target site of BmNPV iap2 gene. There were no differences in economic traits and growth tests between the BmNPV iap2 knockout strain transgenic silkworm lines and the control groups. However, the mortality rate was significantly reduced, the median lethal dose (LD50) was about 100 times higher than the control group, and the onset time was prolonged by 1-2 days after knocking out BmNPV iap2. In addition, the expression levels of apoptotic-related genes Bmiap2, BmICE and BmDreed were significantly affected and the activity of caspase 9 was increased after BmNPV iap2 being edited in transgenic silkworm. These results demonstrated that gene editing BmNPV iap2 could significantly inhibit BmNPV replication and proliferation. This approach provides a new strategy for antiviral research.

Identification of a PP2A gene in Bombyx mori with antiviral function against B. mori nucleopolyhedrovirus

Ser/Thr protein phosphatase 2A (PP2A) is one of the type 2 protein phosphatases, which is required for many intracellular physiological processes and pathogen infection. However, the function of PP2A is unclear in silkworm, Bombyx mori. Here, we cloned and identified BmPP2A, a PP2A gene from B. mori, which has two HEAT domains and a high similarity to PP2A from other organisms. Our results showed that BmPP2A is localized in the cytoplasm and highly expressed in silkworm epidermis and midgut, and that Bombyx mori nucleopolyhedrovirus (BmNPV) infection induces down-regulation of BmPP2A expression. Furthermore, up-regulation of BmPP2A via overexpression significantly inhibited BmNPV multiplication. In contrast, down-regulation of BmPP2A via RNA interference and okadaic acid (a PP2A inhibitor) treatment allowed robust BmNPV replication. This is the first report of PP2A having an antiviral effect in silkworm and provides insights into the function of BmPP2A, a potential anti-BmNPV mechanism, and a possible target for the breeding of silkworm-resistant strains.

A novel system to rapidly detect protein-protein interactions (PPIs) based on fluorescence co-localization

OBJECTIVE

Rapid and convenient detection of protein-protein interactions (PPIs) is of great significance for understanding function of protein.

RESULTS

For efficiently detecting PPIs, we used the changes of proteins fluorescence localization to design a novel system, fluorescence translocation co-localization (FTCL), based on nuclear localization signal (NLS) in living cells. Depending on the original state of protein localization (both in the cytoplasm, both in the nucleus, one in the nucleus and another in the cytoplasm), two target proteins can be partitioned into the cytoplasm and nucleus by adding a NLS or mutating an existing NLS. Three independent results display that the changes of protein fluorescence co-localization were observed following co-expression of the two target proteins. At the same time, we verified the accuracy of fluorescence co-localization by co-immunoprecipitation.

CONCLUSIONS

There FTCL system provided a novel detection method for PPIs, regardless of protein localization in the nucleus or cytoplasm. More importantly, this study provides a new strategy for future protein interaction studies through organelle localization (such as mitochondria, Golgi and cytomembrane, etc.).

Evolutionary and functional analyses of the interaction between the Bombyx mori inhibitor of apoptosis (IAP) and nucleopolyhedrovirus IAPs

As an important insect immune response, apoptosis plays a critical role in the interaction between baculoviruses and insect hosts. Previous reports have identified inhibitor of apoptosis (IAP) proteins in both insects and baculoviruses, but the relationship between these proteins is still not clearly understood. Here, we found that insect IAP proteins were clustered with baculovirus IAP3, suggesting that the baculovirus iap3 gene might be derived from the Lepidoptera or Diptera. We demonstrated that Bombyx mori inhibitor of apoptosis (Bmiap) gene had an inhibitory effect on apoptosis in silkworm cells. Further analysis of the effects of Bmiap genes on the proliferation of B. mori nucleopolyhedrovirus (BmNPV) showed that both the Bmiap and BmNPV iap genes increased BmNPV proliferation after BmNPV infected silkworm cells. Our results also indicated that BmNPV IAP1 and IAP2 directly interacted with BmIAP in silkworm cells, implying that the Bmiap gene might be hijacked by BmNPV iap genes during BmNPV infection. Taken together, our results provide important insights into the functional relationships of iap genes, and improve our knowledge of apoptosis in baculoviruses and insect hosts.

[Morphological observation on the anterior ciliary vessels in the horizontal rectus muscles of patients with concomitant horizontal strabismus]

Objective: To observe the number of blood vessels and the anatomical characteristics of the anterior ciliary vessels (ACVs) in the horizontal rectus muscles of patients with concomitant horizontal strabismus. Methods: Cross-sectional study. From July 2016 to September 2019 patients with concomitant horizontal strabismus treated by realignment surgeries in Xiamen Eye Center of Xiamen University were included. Patients who had previous operations on eyes were excluded. The high resolution surgical imaging of ACVs in the horizontal rectus muscles was performed during operation. The photos of ACVs in muscles were tagged and observed to compare the distribution of the various numbers of blood vessels and morphological characteristics of the ACVs in the medial and lateral rectus muscles. In addition, muscle tissues about 4 mm with an intact sheath were gained from patients undergoing the muscle resection. The muscle sections were stained with hematoxylin-eosin staining, and the arteriovenous properties and their distribution in muscles and fascia tissues were observed. The chi-square test was used for statistical analysis. Results: A total of 387 patients with concomitant horizontal strabismus (176 with esotropia, 211 with exotropia) were enrolled in this study, among whom 198 were male and 189 were female. The age ranged from 1 to 68 years (median, 13 years). Photos of ACVs in 742 horizontal rectus muscles from 383 patients were observed. Of the 351 medial rectus muscles, 24 (6.8%) contained 1 major (or bundle of) ACV, 163 (46.4%) contained 2 major (or bundles of) ACVs, and 164 (46.7%) contained 3 or more major (or bundles of) ACVs. Of the 391 lateral rectus muscles, 161 (41.2%) contained 1 major (or bundle of) ACV, 156 (39.9%) contained 2 major (or bundles of) ACVs, and 74 (18.9%) contained 3 or more major (or bundles of) ACVs. The distribution of ACVs in the medial and lateral rectus muscles was statistically different (χ(2)=133.87, P<0.01). According to the number and morphological characteristics of vessels, the ACVs in the medial and lateral rectus muscles were divided into 4 and 3 categories, respectively, as well as various types and subtypes. The rate of patients whose both eyes had the same type of ACVs in the medial or lateral rectus muscles was 31.6% (25/79) and 26.1% (29/111), respectively, and there was no significant difference (χ(2)=0.69, P=0.41). However, the ACVs of the same type from both eyes of the same patient were not identical in morphology. The ACVs in the medial and lateral rectus muscles with collateral circulation accounted for 3.7% (13/351) and 24.3% (95/391), respectively, and the difference was statistically significant (χ(2)=63.07, P<0.01). The hematoxylin-eosin staining of the medial lateral rectus tissues from 4 patients showed that the ACVs contained arteries and veins. The vessels in the medial rectus muscles were distributed in muscle tissue and fascia tissue, while the vessels in the lateral rectus muscles were only distributed in fascia tissue. Conclusions: Compared with the lateral rectus muscles, there are about 50% medial rectus muscles contain more than 3 major (or bundles of) vessels in patients with concomitant horizontal strabismus. The accompanying patterns of arteries and veins of ACVs are varied. ACVs are distributed in muscle tissue of the medial rectus muscles and in fascia tissue of the medial and lateral rectus muscles. (Chin J Ophthalmol, 2020, 56: 197-204).

BmAtg13 promotes the replication and proliferation of Bombyx mori nucleopolyhedrovirus

Autophagy is a cell adaptive response that involves the process of microbial infections. Our previous study has indicated that Bombyx mori nucleopolyhedrovirus (BmNPV) infection triggers the complete autophagic process in BmN-SWU1 cells, which is beneficial to the viral infection. Autophagy-related (ATG) protein ATG13, as part of the ULK complex (a serine-threonine kinase complex composed of ULK1, ULK2, ATG13, ATG101, and FIP200), is the most upstream component of the autophagy pathway, and how it affects virus infections will improve our understanding of the interaction between the virus and the host. This study has determined that the overexpression of the BmAtg13 gene promotes the expression of viral genes and increases viral production in BmN-SWU1 cells, whereas knocking down the BmAtg13 gene suppresses BmNPV replication. Moreover, the BmAtg13 overexpression transgenic line contributed to viral replication and increased mortality rate of BmNPV infection. In contrast, the BmAtg13 knockout transgenic line reduced viral replication 96 h post-infection. Furthermore, BmATG13 directly interacted with viral protein BRO-B, forming a protein complex. Taken together, the findings of this study suggest that BmATG13 may be utilized by the BRO-B protein to promote BmNPV replication and proliferation, which, in turn, provides important insights into the mechanism that autophagy influences viral infection.

BmGeminin2 interacts with BmRRS1 and regulates Bombyx mori cell proliferation

Geminin is a master regulator of cell-cycle progression that ensures the timely onset of DNA replication and prevents re-replication in vertebrates and invertebrates. Previously, we identified two Geminin genes, BmGeminin1 and BmGeminn2, in the silkworm Bombyx mori, and we found that RNA interference of BmGeminin1 led to re-replication. However, the function of BmGeminin2 remains poorly understood. In this study, we found that knockdown of BmGeminin2 can improve cell proliferation, and upregulated G2/M-associated gene-cyclinB/CDK1 expression. Then, we performed yeast two-hybrid screening to identify interacting proteins. Our results yielded 23 interacting proteins, which are involved in DNA replication, chromosome stabilization, embryonic development, energy, defense, protein processing, or structural protein. Here, we focused on BmRRS1, a chromosome congression-related protein that is closely related to cell cycle G2/M progression. The interaction between BmGeminin2 and BmRRS1 was confirmed by immunofluorescence and immunoprecipitation. Analysis of its expression profile showed that BmRRS1 was related to BmGeminin2. In addition, BmGeminin2 overexpression downregulated the BmRRS1 transcript. Knockdown of BmGeminin2 led to upregulation of the BmRRS1 transcript. Furthermore, overexpression of BmRRS1 can upregulate G2/M-associated gene-cyclinB/CDK1 expression, and improved cell proliferation, consistent with the effects of BmGeminin2 knockout. In addition, BmRRS1 RNA interference can eliminate the impact of BmGem2 knockout on cell proliferation, the ratio of cell cycle stage and the expression of cyclinB/CDK1. These data suggested that the cell proliferation advantage of BmGeminin2 knockout was closely related to BmRRS1. Our findings provide insight into the functions of Geminin and the mechanisms underlying the regulation of the cell cycle in the silkworm.

Comparison of the Hepatoprotective Effects of the Three Main Stilbenes from Mulberry Twigs

The purpose of this study was to compare the hepatoprotective effects of Oxy (oxyresveratrol), Res (resveratrol), and MulA (mulberroside A) (80 mg/kg body weight/d, i.g.) on acute liver injury (ALI) induced by lipopolysaccharide (LPS)/d-galactosamine (d-GalN) in mice. After 7 h of LPS (50 μg/kg body weight, i.p.) and d-GalN (500 mg/kg body weight, i.p.) exposure, the activities of serum transaminases and antioxidant enzymes were determined. The expressions of the Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) signal pathway, the nuclear factor-kappa B (NF-κB) signal pathway, and the mitogen-activated protein kinase (MAPK) signal pathway related proteins were evaluated by Western blot assays. Histopathological analysis was performed by hematoxylin-eosin (H&E) staining on the separated livers of mice. The results showed that treatment with Oxy, Res, and MulA could significantly decreases the levels of alanine transaminase (ALT) and aspartate transaminase (AST) ( P < 0.01). MulA was the most effective ingredient among the three, and the ALT and AST levels were reduced at 90.3 ± 1.3% and 93.9 ± 1.1% compared with the LPS/D-GalN treated group ( P < 0.01). Meanwhile, the stilbenes curbed the expression of inflammatory factors, NF-κB pathway activation, and MAPKs phosphorylation and upregulated antioxidant enzymes, Nrf2, NAD (P) H:quinone oxidoreductase (NQO1), and heme oxygenase-1 (HO-1) expression levels. Stilbenes might protect the ALI caused by LPS/d-GalN through inhibiting the negative effectiveness of oxidation stress and inflammation. The protective performance of MulA was better than those of Oxy and Res, and we hypothesize that it might be due to the mediation of the specific metabolic pathway of the MulA in vivo. All of these results implied that stilbenes in mulberry twigs might be promising as natural additives.

Resistant silkworm strain block viral infection independent of melanization

Melanization mediated by the prophenoloxidase-activating system (proPO) is an important immune response in invertebrates. However, the role of melanization on viral infection has not been wildly revealed in Bombyx mori (B. mori), silkworm. Here, we investigated the extent of melanization of susceptible (871) and resistant (near-isogenic line 871C) B. mori strains. The result showed that the extent of melanization was significantly higher in the susceptible strain than in the resistant strain. A majority of Serpins were up-regulated in the resistant strain through iTRAQ-based quantitative proteomics, comparing with susceptible strain. Our data further identified that Serpin-5, Serpin-9 and Serpin-19 reduced PO activity, indicating that the menlanization pathway was inhibited in the resistant strain. Moreover, our results indicated that the hemolymph of 871 reduced viral infection in the presence of PTU, indicating that melanization of 871 strain hemolymph blocked viral infection. However, viral infection was significantly suppressed in the hemolymph of 871C strain regardless of the presence of PTU or not, which implied that the resistant strain inhibited viral infection independent of the melanization pathway. Taken together, our findings indicated that the melanization pathway was inhibited in resistant strain. These results expend the analysis of melanization pathway in insects and provide insights into understanding the antiviral mechanism.

[Related factors and interaction on HIV/HCV co-infection of patients access to methadone maintenance treatment]

Objective: To estimate the prevalence of HIV/HCV co-infection and explore the influence factors and their interaction on HIV/HCV co-infection of patient's access to methadone maintenance treatment (MMT). Methods: A face to face interviews were conducted among 750 patients at two MMT clinics in Guangxi Zhuang Autonomous Region. The questionnaires information included demographic characteristics, HIV and HCV infection status, history of drug abuse, urine test for morphine, high risk sex behaviors, needle sharing, dropped out etc. Methods of χ(2) test one-way, multivariate logistic regression and interactions were used to analyze the related factors of HIV/HCV co-infection. Results: The study subjects included 750 participants, 18.31% (127/691) of patients were co-infected with HIV and HCV. The HIV/HCV co-infection rate in patients who shared needles with others or dropped out of treatment was 35.84% (81/226) and 19.88% (64/322) respectively, which were higher than those who have never shared needles or dropped out (9.89%, 46/465 and 17.07%, 63/369). Logistic regression analysis results showed that after adjusted for confounding factors, patients who shared needles (OR=4.50, 95%CI: 2.72-7.43) and dropped out of treatment (OR=1.71, 95%CI: 1.04-2.80) were more likely to be infected with HIV/HCV. Interaction analysis showed that sharing needles and dropping out of treatment exist additive effect on co-infection of HIV and HCV (RERI=4.21, AP=0.44, SI=1.95). Conclusions: Needle sharing and dropping out of treatment are associated with HIV/HCV co-infection. Health education, psychological counseling and other measures should be taken to reduce needle sharing and dropping out of MMT.

Construction and characterization of a synthetic Baculovirus-inducible 39K promoter

Background

Silkworm genetic engineering is widely used in gene function, silk engineering and disease-resistant engineering in most of Asia. Some of the earliest promoter elements are used to control the development of silkworm transgenic expression and gene therapy. However, the low expression and specificity of natural promoters limit the applications of genetic engineering. To construct a highly efficient synthetic inducible promoter in the Bombyx mori (Lepidoptera), we analyzed the regulatory elements and functional regions of the B. mori nucleopolyhedrovirus 39 K promoter.

Results

Truncated mutation analysis of the 39 K promoter showed that the transcriptional regulatory region spanning positions - 573 to - 274 and + 1 to + 62 are essential for virus-inducible promoter activity. Further investigations using the electrophoretic mobility shift assay revealed that the baculovirus IE-1 protein binds to the 39 K promoter at the - 310 to - 355 region, and transcription activates the expression of 39 K promoter assay. Finally, we successfully constructed a synthetic inducible promoter that increased the virus-inducing activity of other promoters using the baculovirus-inducible transcriptional activation region that binds to specific core elements of 39 K (i.e., spanning the region - 310 to - 355).

Conclusions

In summary, we constructed a novel, synthetic, and highly efficient biological tool, namely, a virus-inducible 39 K promoter, which provides endless possibilities for future research on gene function, gene therapy, and pest control in genetic engineering.

C-lysozyme contributes to antiviral immunity in Bombyx mori against nucleopolyhedrovirus infection

Lysozymes is a ubiquitous immune effector that is widely distributed in both vertebrates and invertebrates. Previous reports have shown that lysozymes significantly inhibit viral infections in vertebrates. However, the antiviral effects of lysozymes in invertebrates remain unclear. Here, we investigated the role of lysozymes in Bombyx mori (B. mori) response to viral infection by overexpressing B. mori C-lysozyme (BmC-LZM) in larvae and cells. We found that BmC-LZM was up-regulated in cells in response to viral infection. Indeed, the overexpressing of BmC-LZM significantly inhibited viral replication in cells during late-stage infection. However, this effect was reversed by BmC-LZM mRNA. BmC-LZM was successfully overexpressed in B. mori strain 871 using Baculovirus Expression Vector System (BEVS). This overexpression markedly reduced viral proliferation and increased larval survival percentage. Thus, BmC-LZM inhibited viral replication both in vivo and in vitro, indicating that BmC-LZM is involved in the insect immune response to viral infection. Our results provide a basis for further applications of lysozymes.

Oxyresveratrol, a Stilbene Compound from Morus alba L. Twig Extract Active Against Trichophyton rubrum

Morus alba L. (mulberry) twig is known to have an inhibitory effect on pathogens in traditional Chinese medicine. In the present study, the dermophytic fungus, Trichophyton rubrum, was used to evaluate the inhibitory effect of total M. alba twig extract and extracts obtained using solvents with different polarities by the method of 96-well MTT colorimetry. The main active substance was isolated and identified by tracking its activity. In addition, the inhibitory effects of active extracts and a single active substance were investigated in combination with miconazole nitrate. Our data indicated that ethyl acetate extracts of mulberry twig (TEE) exhibited a desired inhibitory activity on T. rubrum with the minimum inhibitory concentration (MIC) of 1.000 mg/mL. With activity tracking, the main substance showing antimicrobial activity was oxyresveratrol (OXY), which was isolated from TEE. Its MIC for inhibiting the growth of T. rubrum was 0.500 mg/mL. The combined use of miconazole nitrate and OXY showed a synergistic inhibitory effect, as shown by a significant decrease in the MIC of both components. Based on the OXY content in TEE, the contribution rate of OXY to the inhibitory effect of TEE on T. rubrum was 80.52%, so it was determined to be the main antimicrobial substance in M. alba twig. Copyright © 2017 John Wiley & Sons, Ltd.

Two Geminin homologs regulate DNA replication in silkworm, Bombyx mori

DNA replication is rigorously controlled in cells to ensure that the genome duplicates exactly once per cell cycle. Geminin is a small nucleoprotein, which prevents DNA rereplication by directly binding to and inhibiting the DNA replication licensing factor, Cdt1. In this study, we have identified 2 Geminin genes, BmGeminin1 and BmGeminn2, in silkworm, Bombyx mori. These genes contain the Geminin conserved coiled-coil domain and are periodically localized in the nucleus during the S-G2 phase but are degraded at anaphase in mitosis. Both BmGeminin1 and BmGeminin2 are able to homodimerize and interact with BmCdt1 in cells. In addition, BmGeminin1 and BmGeminin2 can interact with each other. Overexpression of BmGeminin1 affects cell cycle progression: cell cycle is arrested in S phase, and RNA interference of BmGeminin1 leads to rereplication. In contrast, overexpression or knockdown of BmGeminin2 with RNAi did not significantly affect cell cycle, while more rereplication occurred when BmGeminin1 and BmGeminin2 together were knocked down in cells than when only BmGeminin1 was knocked down. These data suggest that both BmGeminin1 and BmGeminin2 are involved in the regulation of DNA replication. These findings provide insight into the function of Geminin and contribute to our understanding of the regulation mechanism of cell cycle in silkworm.

Identification and characterization of the BmCyclin L1-BmCDK11A/B complex in relation to cell cycle regulation

Cyclin proteins are the key regulatory and activity partner of cyclin-dependent kinases (CDKs), which play pivotal regulatory roles in cell cycle progression. In the present study, we identified a Cyclin L1 and 2 CDK11 2 CDK11 splice variants, CDK11A and CDK11B, from silkworm, Bombyx mori. We determined that both Cyclin L1 and CDK11A/B are nuclear proteins, and further investigations were conducted to elucidate their spatiofunctional features. Cyclin L1 forms a complex with CDK11A/B and were co-localized to the nucleus. Moreover, the dimerization of CDK11A and CDK11B and the effects of Cyclin L1 and CDK11A/B on cell cycle regulation were also investigated. Using overexpression or RNA interference experiments, we demonstrated that the abnormal expression of Cyclin L1 and CDK11A/B leads to cell cycle arrest and cell proliferation suppression. Together, these findings indicate that CDK11A/B interacts with Cyclin L1 to regulate the cell cycle.

Effects of starvation and hormones on DNA synthesis in silk gland cells of the silkworm, Bombyx mori

Silk gland cells of silkworm larvae undergo multiple cycles of endomitosis for the synthesis of silk proteins during the spinning phase. In this paper, we analyzed the endomitotic DNA synthesis of silk gland cells during larval development, and found that it was a periodic fluctuation, increasing during the vigorous feeding phase and being gradually inhibited in the next molting phase. That means it might be activated by a self-regulating process after molting. The expression levels of cyclin E, cdt1 and pcna were consistent with these developmental changes. Moreover, we further examined whether these changes in endomitotic DNA synthesis resulted from feeding or hormonal stimulation. The results showed that DNA synthesis could be inhibited by starvation and re-activated by re-feeding, and therefore appears to be dependent on nutrition. DNA synthesis was suppressed by in vivo treatment with 20-hydroxyecdysone (20E). However, there was no effect on DNA synthesis by in vitro 20E treatment or by either in vivo or in vitro juvenile hormone treatment. The levels of Akt and 4E-BP phosphorylation in the silk glands were also reduced by starvation and in vivo treatment with 20E. These results indicate that the activation of endomitotic DNA synthesis during the intermolt stages is related to feeding and DNA synthesis is inhibited indirectly by 20E.

A newly discovered member of the Atlastin family, BmAtlastin-n, has an antiviral effect against BmNPV in Bombyx mori

Atlastin is a member of the dynamin protein superfamily and it can mediate homotypic fusion of endoplasmic reticulum (ER) membranes, which is required for many biological processes. In this study, a new Atlastin homologous protein, BmAtlastin-n, was characterized in silkworms and was found to contain an N-terminal conserved GTPase domain and a coiled-coil middle domain. BmAtlastin-n is localized in the cytoplasm and enriched in silkworm midgut. Results also showed that overexpression of BmAtlastin-n in BmN-SWU1 cells could enhance resistance to BmNPV. To better confirm its antiviral effect, microRNA was used to knock down the expression of BmAtlastin-n in BmE-SWU1 cells with inducing the reproduction of BmNPV. A transgenic expression vector of BmAtlastin-n was constructed and introduced to silkworm embryos by microinjection. The transgenic silkworm also showed considerable antiviral capacity. In conclusion, these findings demonstrate that BmAtlastin-n plays an important role in BmNPV defense. More importantly, the current study may provide a new clue for Atlastin research.

Establishment of a highly efficient virus-inducible CRISPR/Cas9 system in insect cells

Although current antiviral strategies can inhibit baculovirus infection and decrease viral DNA replication to a certain extent, novel tools are required for specific and accurate elimination of baculovirus genomes from infected insects. Using the newly developed clustered regularly interspaced short palindromic repeats/associated protein 9 nuclease (CRISPR/Cas9) technology, we disrupted a viral genome in infected insect cells in vitro as a defense against viral infection. We optimized the CRISPR/Cas9 system to edit foreign and viral genome in insect cells. Using Bombyx mori nucleopolyhedrovirus (BmNPV) as a model, we found that the CRISPR/Cas9 system was capable of cleaving the replication key factor ie-1 in BmNPV thus effectively inhibiting virus proliferation. Furthermore, we constructed a virus-inducible CRISPR/Cas9 editing system, which minimized the probability of off-target effects and was rapidly activated after viral infection. This is the first report describing the application of the CRISPR/Cas9 system in insect antiviral research. Establishment of a highly efficient virus-inducible CRISPR/Cas9 system in insect cells provides insights to produce virus-resistant transgenic strains for future.

Screening and optimization of an efficient Bombyx mori nucleopolyhedrovirus inducible promoter

Pathogen-inducible promoters have been studied extensively and widely used in resistance breeding and gene therapy. However, few reports have been published that explore the efficacy of Bombyx mori nucleopolyhedrovirus (BmNPV)-inducible promoters in antiviral research in the Bombyx mori (Lepidoptera). Here, we screened BmNPV promoters (VP1054, P33, Bm21, Bm122, 39K, P143, and P6.9) and found that the 39K promoter had the highest BmNPV-induced transcriptional activity by dual-luciferase reporter assays system. By 5' truncation analysis, two regions of 39K promoter were critical for optimal virus-inducible activity, indicated that they could serve as a candidate to produce synthetic pathogen-induced promoters. Furthermore, we enhanced the virus-inducible activity of BmNPV 39K promoter using a hybrid enhancer comprising hr3 and polh-up (designated as HP39K). Finally, we showed that RNAi regulated by HP39K promoter could significantly inhibit the proliferation of BmNPV in silkworm cells. Taken together, our results have practical value in antiviral research of silkworm and baculovirus expression system.

Effects of 10-hydroxycamptothecin on intrinsic mitochondrial pathway in silkworm BmN-SWU1 cells

10-Hydroxycamptothecin (HCPT), a plant alkaloid isolated from Camptotheca acuminate, is known as a planted-derived insecticide, however, the specific mechanism in insect cells is still unclear. In this study, we treated the ovarian cell line of the silkworm, BmN-SWU1, with different HCPT doses for durations ranging from 0 to 72h. The apoptosis morphology was evident after 72h of incubation and included cell protuberance, concentrated cytoplasm and apoptotic bodies. We observed DNA fragmentation and cell apoptosis after HCPT treatment. The disruption of mitochondrial distribution, activation of the intracellular mitochondrial permeability transition pore, and release of cytochrome c during HCPT-induced apoptosis in dose and time-dependent manner indicate the involvement of mitochondria in BmN-SWU1 cells. Caspase-9 and -3 activities increased gradually with the duration of incubation time. In conclusion, HCPT has a significant effect to initiate the intrinsic mitochondrial pathway in silkworm cells, providing a theoretical basis for better application of plant-derived insecticide in pest control.

Oligomerization of Baculovirus LEF-11 Is Involved in Viral DNA Replication

We have previously reported that baculovirus Bombyx mori nucleopolyhedrovirus (BmNPV) late expression factor 11 (lef-11) is associated with viral DNA replication and have demonstrated that it potentially interacts with itself; however, whether LEF-11 forms oligomers and the impact of LEF-11 oligomerization on viral function have not been substantiated. In this study, we first demonstrated that LEF-11 is capable of forming oligomers. Additionally, a series of analyses using BmNPV LEF-11 truncation mutants indicated that two distinct domains control LEF-11 oligomerization (aa 42–61 and aa 72–101). LEF-11 truncation constructs were inserted into a lef-11-knockout BmNPV bacmid, which was used to demonstrate that truncated LEF-11 lacking either oligomerization domain abrogates viral DNA replication. Finally, site-directed mutagenesis was used to determine that the conserved hydrophobic residues Y58&I59 (representing Y58 and I59), I85 and L88&L89 (representing L88 and L89) are required for LEF-11 oligomerization and viral DNA replication. Collectively, these data indicate that BmNPV LEF-11 oligomerization influences viral DNA replication.

Expression pattern and tissue localization of the class B scavenger receptor BmSCRBQ4 in Bombyx mori

Class B scavenger receptors (SR-Bs) are cell surface glycoproteins involved in various physiological processes in vivo, including the transport and metabolism of lipids, binding and phagocytosis of xenobiotics, and signaling. But little information is available about silkworm SR-Bs; it is necessary to study these SR-Bs for revealing their function. In this study, we cloned the full-length coding sequence of BmSCRBQ4, a SR-B gene from the silkworm Bombyx mori L. We found that the BmSCRBQ4 gene consists of nine exons and eight introns, with an open reading frame of 1371 bp encoding 456 amino acids. Gene expression studies determined that BmSCRBQ4 messenger RNA (mRNA) was expressed in unfertilized eggs, during embryonic development and throughout the majority of the larval period. Expression of mRNA was detected in the mid gut, middle silk gland, posterior silk gland, head, integumentum, fat body, testes and the ovaries of the larval B. mori Dazao strain, as well as in the silkworm cell lines BmN and BmE. Protein expression studies found BmSCRBQ4 protein was expressed only in the testes, fat body and middle silk gland of larvae, as well as in the silkworm cell lines BmN and BmE. The BmSCRBQ4 protein showed variability in banding patterns in different tissues and cells when analyzed by Western blotting. Immunohistochemical staining showed that the BmSCRBQ4 protein localizes to the constitutive membranes or cellular membranes of these tissues. These results indicated that BmSCRBQ4 gene may play some physiologically relevant roles at the cell surface in each tissue.

The silkworm GSTe4 is sensitive to phoxim and protects HEK293 cells against UV-induced cell apoptosis

Glutathione S-transferases (GSTs, EC 2.5.1.18) are a family of super enzymes with multiple functions that play a major role in the detoxification of endogenous and xenobiotic compounds. In our previous study, we have predicted 23 putative cytosolic GSTs in the silkworm genome using bioinformatic methods. In this study, we cloned and studied the insect-specific epsilon-class GST gene GSTe4 from the silkworm, Bombyx mori. The recombinant BmGSTe4 (Bac-BmGSTe4) was overexpressed in SF-9 cell lines, and it was found to have effective GST activity. We also found that the expression of BmGSTe4 was especially down-regulated after the silkworms were fumigated with or ingested phoxim. Moreover, BmGSTe4 protected HEK293 cells against UV-induced cell apoptosis. These results demonstrated that BmGSTe4 has GST activity, is sensitive to phoxim, and plays a role in inhibition of UV-induced cell apoptosis.

Differential susceptibilities to BmNPV infection of two cell lines derived from the same silkworm ovarian tissues

We previously established and characterized two insect cell lines (BmN-SWU1 and BmN-SWU2) from Bombyx mori ovaries. Here, we examined their differential susceptibilities to Bombyx mori nucleopolyhedrovirus (BmNPV) despite having originated from the same tissue source. BmN-SWU1 cells were susceptible and supported high titers of BmNPV replication, while BmN-SWU2 cells were resistant to BmNPV infection. Subcellular localization analysis demonstrated that very few BmNPV particles could be imported into BmN-SWU2 cells. However, initiation of BmNPV DNA replication but not amplification was detected in BmN-SWU2 cells after transfection with vA4^prm-VP39-EGFP bacmid DNA. BmNPV transcription assays showed that late and very late but not early viral genes apparently were blocked in BmNSWU2 cells by unknown mechanisms. Further syncytium formation assays demonstrated that the BmNPV envelope fusion protein GP64 could not mediate BmN-SWU2 host cell-cell membrane fusion. Taken together, these results indicate that these two cell lines represent optimal tools for investigating host-virus interactions and insect antiviral mechanisms.