Fig. 5. fue mutants exhibit a defect in mitotic spindle assembly. Mitotic spindles were visualised using an antibody directed against -tubulin (green) and chromosomes were labelled with DAPI (blue). (A) The first mitotic spindle is assembled in wild-type zygotes at 25 minutes post-fertilization. (B,C) In fue zygotes mitotic spindle assembly is perturbed because of a defect in chromosome-dependent microtubule nucleation (B), however, in about 30% of fue zygotes microtubule nucleation on one or both chromosome clusters (arrowhead, C) does occur. In all cases the formation of asters does not seem to be affected (B,C). (E) A mitotic spindle as observed in wild-type eight-cell stage embryos. (F,G) In the majority of fue embryos at post-zygotic stages, microtubules are associated with the chromosome clusters during mitosis (F), except in a minority of embryos (about 5%), where aberrant spindles are observed, which can randomly segregate DNA (G). (D,H) In all fue cells at post-zygotic stages a pair of asters is formed during mitosis (H), which is similar to that observed in the anucleate cells of wild-type embryos that were injected with the DNA replication inhibitor, aphidicolin (D). Therefore, fue zygotes demonstrate a defect in spindle assembly, arising from a defect in the chromatin-dependent generation of microtubules (Karsenti and Vernos, 2001). Scale bars: 20 µm.