Characterization Of Bombyx Mori Nucleopolyhedrovirus (BmNPV) Infection In The Trachea Of Silkworm

During the process of Bombyx mori nucleopolyhedrovirus(BmNPV)infection,Occlusion-derived virus(ODV)were released in the midgut of silkworm to infect the epithelium cells and establish the primary infection.Budded virus(BV)was then produced after budding from the basement membrane of the midgut epithelial cells with polarities.BV triggers host-related physiological processes through its own encoded protein to allow the virus escape from the midgut,and infect various tissues to establish a systemic infection.In the process of establishing a systemic infection of baculovirus,the trachea has been considered to play an important role as an channel that connect various tissues throughout the larvae.In order to study the characteristics of trachea infected by baculovirus in silkworm and analyze the role of trachea in virus transmission,our study based on immunohistochemistry,transcriptomics,molecular biology,and bioinformatics analysis to explore the histopathological changes of trachea,the characteristics of BmNPV infection and different expressed genes(DEGs)in tracheal epithelial cells.The main results are as follows:1.Through optical microscope observation and HE staining,it was found that the viral infection have a dramatic impact on the structural integrity of trachea tissue,including tissue dissociation,cell swelling,DNA replication up-regulated,polyhedron aggregation and other symptoms.2.Tracking the fluorescent tag of the recombinant virus,it was observed that BmNPV transmitted linearly on the trachea,and fluorescence of the end branches of trachea gradually weaken.At this time,it also can be seen that fluorescence intensity at the bottom of the trachea gradually becomes stronger at 72h p.i.During the infection on trachea,BmNPV gradually spreads along the end of the trachea and then spreads to the other tissues when the systemic infection built.3.There are a small number of fluorescent signals can be detected outside the nucleus of tracheal epithelial cells at earliest to 24 hp.i when tissue immunofluorescence were used for tracking wild-type BmNPV infection in different phases.The fluorescent signals clearly distributed in the cytoplasm of tracheal epithelial cells,and the cell volume becomes larger at 48h p.i gradually,which proves that tracheal epithelial cells are important target site of BmNPV infection.The results of real-time quantitative PCR indicate that the trachea produces a large number of BV with stronger cell infection ability.These results suggested that the progeny virus produced in the trachea is more beneficial to cell-to-cell transmission,which further proves the important role of trachea in the BmNPV transmission in vivo.4.Transcriptomics sequencing was applied to analyze the mRNA level of the tracheal epithelial cells before and after virus infection.This result showed that the genes related to DNA replication and aminoacyl tRNA synthesis,cytoskeleton pathway and glycoprotein synthesis were up-regulated,while the genes related to energy metabolism and immune response pathways were down-regulated after virus infection.These change may be closely related to the proliferation,coating and transmission of viral particles in the trachea.