Susceptibility of the Bombyx mori cardia cells to Nucleopolyhedrovirus, multiple subgroup, BmMNPV

Bombyx mori entomopathogenic virus infection is a serious problem for silk production in tropical regions. Here, we investigate the susceptibility of the B. mori cardia epithelial cells to B. mori Nucleopolyhedrovirus, BmMNPV. Results show that cardia cells are susceptible to BmMNPV and that the cytopathology is similar to that in other target cells. The infection was detected at 6 day post-inoculation. This infection time, together with the protected cover intima, suggests that the cardia region is a secondary target, infected by budded virus.     

Specific expression of GFPuv-beta1,3-N-acetylglucosaminyltransferase 2 fusion protein in fat body of Bombyx mori silkworm larvae using signal peptide

Bombyxin (bx) and prophenoloxidase-activating enzyme (ppae) signal peptides from Bombyx mori, their modified signal peptides, and synthetic signal peptides were investigated for the secretion of GFP(uv)-beta1,3-N-acetylglucosaminyltransferase 2 (GGT2) fusion protein in B. mori Bm5 cells and silkworm larvae using cysteine protease deficient B. mori multiple nucleopolyhedrovirus (BmMNPV-CP(-)) and its bacmid. The secretion efficiencies of all signal peptides were 15-30% in Bm5 cells and 24-30% in silkworm larvae, while that of the +16 signal peptide was 0% in Bm5 cells and 1% in silkworm larvae. The fusion protein that contained the +16 signal peptide was expressed specifically in the endoplasmic reticulum (ER) and in the fractions of cell precipitations. Ninety-four percent of total intracellular beta1,3-N-acetylglucosaminyltransferase (beta3GnT) activity was detected in cell precipitations following the 600, 8000, and 114,000g centrifugations. In the case of the +38 signal peptide, 60% of total intracellular activity was detected in the supernatant from the 114,000g spin, and only 1% was found in the precipitate. Our results suggest that the +16 signal peptide might be situated in the transmembrane region and not cleaved by signal peptidase in silkworm or B. mori cells. Therefore, the fusion protein connected to the +16 signal peptide stayed in the fat body of silkworm larvae with biological function, and was not secreted extracellularly.