Fig. 1. Time-lapse series of optical sections throughout the twelfth cleavage cycle following injection of egg cytoplasm into embryos. Microtubules are highlighted by 1-tubulin-GFP. The embryos were injected during anaphase of the eleventh cleavage cycle. The injected cytoplasm samples were taken from wild-type eggs (Wild type) or eggs from Kavar^18c/- females (Kavar^18c/-). E82K-4-tubulin, introduced in the Kavar^18c/- egg cytoplasm, slowed down the separation of the daughter centrosomes (white arrows). The partially separated centrosomes either organize the formation of short microtubules that never assemble to a spindle apparatus (middle column of panels), or fail to localize the nuclei properly (right column of panels; adjoining nuclei in the boxed area); as a consequence tripolar spindles form. Asterisks indicate sites of cytoplasm injection; time after injection is shown in the first column of panels but applies to the entire row; arrows indicate centrosomes, open arrows indicate interpolar microtubule bundles.