Optical sections of mitotic chromosomes of zebrafish (Danio rerio) embryos at the cleavage stage after staining with antibodies against the integral membrane protein of the inner nuclear membrane LAP{omega} (red) and the DNA-staining dye Hoechst (blue). These early developmental stages are characterized by the association of nuclear-envelope-forming vesicles with mitotic chromosomes prior to anaphase, resulting in the formation of a nuclear envelope around each single chromosome (upper nucleus; approximately 15 chromosomes are visible). Subsequently nuclear membranes of neighbouring karyomeres start to fuse (lower nucleus). For further details, see the article by Schoft et al. JCS2003.