Figure 6).

Cell death in ‘second-floor’ cells. A A positive terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling reaction indicating apoptosis in the two nuclei of a second-floor cell at an early stage (72 h) in culture. Red represents actin. B Uptake of propidium iodide indicating necrosis of a second-floor cell. Red represents propidium iodide and green represents actin. C By reduction of the laser intensity in the confocal microscope, it became evident that the second nucleus was already fading. D Electron microscopy confirms the necrotic appearance of the nucleus (original magnification ×24,000). E Shadow projection. Absence of nuclei in a rod-shaped, cross-striated second-floor cell. The underlying spreading cell contains two intact nuclei. F This is more distinct in a section-mode presentation, where the xz-plane (below) and the yz-plane (right) clearly show the unstained nuclear region in the centre of the cell