Fig. 4. Formation of -H2AX foci in the nuclei incubated in Xenopus egg extract containing CPT. Demembranated sperm nuclei were incubated in Xenopus egg extract with (B) or without (A) CPT. -H2AX foci formation (a,c,e,g) and DNA (b,d,f,h) in the absence (a,b,c,d) or the presence (e,f,g,h) of geminin were visualized. Panels c, d, g and h are enlarged images of the nuclei indicated by arrowheads in panels a, b, e and f, respectively. Bars, 50 µm (a,b,e,f); 20 µm (c,d,g,h).