Microtubule assembly after treatment of pig oocytes with taxol: Correlation with chromosomes, γ‐tubulin, and MAP kinase*

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Abstract
In this study, taxol was used as a tool to study the correlation of microtubule assembly with chromosomes, γ‐tubulin and phosphorylated mitogen‐activated protein (MAP) kinase in pig oocytes at different maturational stages. Taxol treatment did not affect meiotic resumption and chromosome condensation but inhibited/disrupted chromosome alignment at the metaphase plate and bipolar spindle formation and thus meiotic progression. Microtubules were co‐localized with chromosomes and were found to emanate from the chromosomes in taxol‐treated oocytes, suggesting that chromosomes may serve as a source of microtubule organization. In addition, the concentric emanation of microtubules within the chromosome‐surrounded area in taxol‐treated oocytes suggests that microtubule emanation from the chromosomes may be directed by other microtubule‐organizing material. The formation of one large spindle or ≥2 spindles in oocytes after taxol removal shows that minus end microtubule‐organizing material can be normally located on both sides of chromosomes only when the chromosomes are aligned on the metaphase plate. The co‐localization of γ‐tubulin and phosphorylated MAP kinase with microtubule assembly in both control and taxol‐treated oocytes suggests that these two proteins are associated microtubule‐nucleating material in pig oocytes. However, Western blot analysis showed that neither cytoplasmic microtubule aster formation nor extensive microtubule assembly in the chromosome region induced by taxol was caused by super‐activation of MAP kinase. Taxol also induced microtubule assembly depending on chromosome distribution in the first polar body. The results suggest that chromosomes are always co‐localized with microtubules and that emanation of microtubules from the chromosomes may be regulated/directed by microtubule‐organizing material including γ‐tubulin and phosphorylated MAP kinase in pig oocytes. Mol. Reprod. Dev. 60: 481–490, 2001.

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