Fig. 4. Classification of apoptotic nuclei. BRL cells treated with 1 µM staurosporine for 15 hours were fixed, permeabilized and stained for DNA using BoBo-3-iodide or for lamin B before analysis by CLSM. The panels show chromatin in 0.3 µm equatorial sections of apoptotic nuclei classified as stage I-III as indicated. The extremely weak lamin B immunofluorescence signal remaining in a stage III nucleus delineating the grape-shaped nuclear periphery is also shown. Bars, 10 µm (stage I,II); 5 µm (stage III).