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.

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.

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 Bm14-3-3ζthat can interact with BmE2F4 and allow it to localize in the nucleus.Overexpression of the Bm14-3-3ζgene 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.