FIG 9.

C6/36 cell-cell fusion from within. C6/36 cells were infected with the WT and mutant viruses at an MOI of 1. The cell culture supernatants were harvested every 24 h, and then the viral titer and GCP number were calculated by plaque assays (A) and qPCR (B), respectively. (C) At 4 days postinfection, fusion of the infected cells was triggered by serum-free medium at pH 5.5 for 2 h, and then the nuclei were stained with DAPI for 10 min. The percent fusion was determined by the numbers of the nuclei of the syncytia relative to the total number of nuclei. Asterisks denote a statistically significant reduction in fusion activity compared to that of the WT (**, P < 0.01; ***, P < 0.001). (D) Presentation of the syncytia formed by WT and other mutants. Syncytia were usually formed by dozens of cells, and a representative syncytium is indicated by a white arrow.