Imaging and 3D reconstruction of interphase and mitotic nuclei within a fixed H2B-HcRed-expressing spheroid. A: Magnification of one frame of the z-stack presented in Additional file 4 showing a mitotic cell located on the surface of the spheroid detected at z = 30 μm. Scale bar, 15 μm. B: 3D reconstruction of the region of the stack corresponding to the frame shown in a: blue isosurfaces correspond to interphase nuclei and red isosurfaces to mitotic condensed chromosomes. Scale bar: 7 μm. C: Magnification of a region of a z-stack at z = 150 μm showing a mitotic cell located at 100 μm from the surface of the spheroid. Scale bar, 10 μm. D: 3D reconstruction of the region of the stack corresponding to C. Scale bar: 7 μm. E: Sketch showing how the position of the mitotic cells are defined with regard to the spheroid surface and to the z position in the detection axis.