The effect of taxol on first and second meiotic spindle formation was examined in oocytes of the surf clam, Spisula solidissima, by immunofluorescence staining with anti-tubulin antibody. The first meiotic spindle appeared to form as in untreated control cells. However, the spindle did not migrate toward the periphery of taxol-activated oocytes, resulting in blockage of the formation of the first polar body. In spite of inhibited microtubule depolymerization and failure of spindle disappearance, the pole separation in telophase that is typical of this material began at the same time as in untreated cells. Polymerization of the second spindle microtubules onto the spindle persisting from the first meiosis led to the formation of a triple form of spindle connected at the poles of each other. The subsequent emergence of ring-shaped microtubule-containing structures in mature activated eggs was not affected by taxol. The mechanism of meiotic spindle formation thus seemsto be different from that in mitosis, where taxol has been shown to block spindle formation completely.

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