Fig. 5.

Immunofluorescence for immortalizing E1A protein and transient transfection to examine expression plasmid promoter activity. (A) All cells are positive for E1A in early passage Rousettus cell lines but signal intensity is close to the detection limit in R06E and R05R. CR cells serve as positive control, Vero as negative control. (B) In high passage cell lines signal intensity remains high in R05T but was lost in R06E. (C) Chiropteran and avian cell lines were transiently transfected with an expression plasmid where GFP reporter is under control of the promoters used in the immortalizing plasmid. hPGK, human phosphoglycerate kinase promoter; tk, herpes simplex virus thymidine kinase promoter. Note extremely low signal strength for hPGK and tk promoters in Rousettus cells but not in CR cells. Even the usually very strong hCMV promoter appears to be repressed in Rousettus cells. Images shown here were taken 24 h post-transfection.