Effects of nanomolar taxol on crane-fly spermatocyte spindles indicate that acetylation of kinetochore microtubules can be used as a marker of poleward tubulin flux.

Kinetochore microtubules (kMTs) in meiosis-I crane-fly spermatocytes label strongly with antibodies to acetylated alpha-tubulin, except near the kinetochore, where there is a "gap" in labelling [Wilson and Forer, 1989: Cell Motil. Cytoskeleton 14:237-250]. Previously we measured the length of gaps in metaphase and anaphase cells, and from these data deduced that during anaphase kMTs disassemble primarily at the pole [Wilson et al., 1994: J. Cell Sci. 107:3015-3027]. However, the study rested on our assumption that the gap is due to a time lag between polymerisation at the kinetochore and acetylation of the polymerised MTs: the subunits enter kMTs at the kinetochore and do not become acetylated until they have moved poleward. In the present study we tested our interpretation of the gap by treating spermatocytes with paclitaxel (taxol) to reduce microtubule dynamics [e.g. Jordan et al., 1993: Proc. Natl. Acad. Sci. U.S.A. 90:9552-9556]. We expected that if our assumptions were correct, taxol would slow tubulin addition at the kinetochore but acetylation would continue, and the gap in acetylation would get smaller. We found that 5 to 50 nM taxol results in increased acetylation of kMTs at the kinetochore, supporting our interpretation of the gap. Nanomolar taxol also increases the level of acetylation in other microtubule populations and causes changes in spindle morphology.