BmNHR96 participate BV entry of BmN-SWU1 cells via affecting the cellular cholesterol level.

B.mori nucleopolyhedrovirus (BmNPV), which produces BV and ODV two virion phenotypes in its life cycle, caused the amount of economic loss in sericulture. But the mechanism of its infection was still unclear. In this study we characterized B.mori nuclear hormone receptor 96 (BmNHR96) as a NHR96 family member, which was localized in the nucleus. We also found BmNHR96 over-expression could enhance the entry of BV as well as cellular cholesterol level. Furthermore, we validated that BmNHR96 increased membrane fusion mediated by GP64, which could probably promote BV-infection. In summary, our study suggested that BmNHR96 plays an important role in BV infection and this function probably actualized by affecting cellular cholesterol level, and our results provided insights to the mechanisms of BV-infection of B.mori.

Transgenic RNAi of BmREEPa in silkworms can enhance the resistance of silkworm to Bombyxmori Nucleopolyhedrovirus.

Our previous study has identified a gene, BmREEPa, which affects BmNPV invasion in silkworm cells. In this study, we interfered with BmREEPa in silkworm larvae through transgenic technology and screened BmREEPa-RNAi silkworm strains (RP). We found the mortality in RP was lower than that in Dazao, when silkworm larvae were infected with BmNPV via oral and injection routes. And the expression level of VP39 was lower in RP than in Dazao in the group infected via injection. In the oral infection group, VP39 expression level showed significant reduction at 48 h post-infection. These results revealed that the anti-BmNPV activity was enhanced in RP, and this enhancement probably presents itself during secondary infection via BVs.

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.

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.

BmREEPa Is a Novel Gene that Facilitates BmNPV Entry into Silkworm Cells.

We previously established two silkworm cell lines, BmN-SWU1 and BmN-SWU2, from Bombyx mori ovaries. BmN-SWU1 cells are susceptible while BmN-SWU2 cells are highly resistant to BmNPV infection. Interestingly, we found that the entry of BmNPV into BmN-SWU2 cells was largely inhibited. To explore the mechanism of this inhibition, in this study we used isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative protein expression profiling and identified 629 differentially expressed proteins between the two cell lines. Among them, we identified a new membrane protein termed BmREEPa. The gene encoding BmREEPa transcribes two splice variants; a 573 bp long BmREEPa-L encoding a protein with 190 amino acids and a 501 bp long BmREEPa-S encoding a protein with 166 amino acids. BmREEPa contains a conserved TB2/DP, HVA22 domain and three transmembrane domains. It is localized in the plasma membrane with a cytoplasmic C-terminus and an extracellular N-terminus. We found that limiting the expression of BmREEPa in BmN-SWU1 cells inhibited BmNPV entry, whereas over-expression of BmREEPa in BmN-SWU2 cells promoted BmNPV entry. Our results also indicated that BmREEPa can interact with GP64, which is the key envelope fusion protein for BmNPV entry. Taken together, the findings of our study revealed that BmREEPa is required for BmNPV to gain entry into silkworm cells, and may provide insights for the identification of BmNPV receptors.