Plasmid transfection of F-ΔOcc leads to extrusion and apoptosis. A. CIT3 cells on glass slides transiently transfected with F-ΔOcc were fixed and stained 18 hr later. An antibody to ZO-1 outlines junctional complexes (green) and an antibody to FLAG (red) labels a transfected cell. Nuclei are stained with DAPI. Yellow in composite images represents overlap between ZO-1 and FLAG. B. CIT3 cells grown on glass slides were transiently transfected with FLAG-bacterial alkaline phosphatase as a control (upper left hand panel) or F-ΔOcc. After 48 hr monolayers were fixed and stained for TUNEL (red), FLAG (green), and nuclei (blue). A spontaneous TUNEL positive nucleus outside two F-BAP expressing cells (upper right panel) demonstrates that the TUNEL stain is working in this view. C. Transfected cells shown in B were identified by their expression of FLAG; the proportion of these cells showing TUNEL positivity was determined and plotted as a percentage of the FLAG stained cells. *** p < .0005. D. Cells transfected with F-ΔOcc as in B were visualized by staining for the FLAG epitope, actin, myosin, and nuclei as labeled.