MICROTUBULE TRACKS CAN BE DETECTED IN MOUSE OOCYTES WITH AN ANTIBODY-DIRECTED AGAINST A CALCIUM TRANSPORTER

In metaphase II-arrested mouse oocytes, most microtubules are found in the meiotic spindle, a structure that remains stable for hours despit e microtubule instability. Microtubule organizing centres (MTOCs) are present at the poles of the spindle and in the cytoplasm, but the latt er nucleate very few microtubules. This particular organization of the microtubule network enabled us to observe the unexpected behaviour of a protein that can associate with microtubules. We compared the distr ibution of a mitosis-activated calcium transport system with that of t he microtubule network, by immunofluorescence, using two monoclonal an tibodies, one directed against a component of the calcium transport sy stem (7/13), and the other against the common tyrosinated form of alph a-tubulin (YL1/2). The 7/13 staining was associated with the spindle m icrotubules and with the kinetochore area. In addition, we observed ma ny asters in the cytoplasm, around the cytoplasmic MTOCs. The majority of these asters were not stained with the antitubulin antibody. Moreo ver, these 7/13 asters either disappeared after nocodazole treatment o r were enlarged after taxol treatment. Using a confocal microscope, we observed single fibres that were stained with both antibodies: the ex tremity furthest from the MTOC (corresponding to the + end of the micr otubule) being detected by the 7/13 antibody only. All these observati ons suggest that the 7/13 antigen is associated with microtubule track s that persist a few minutes after microtubule depolymerization. The p ossible role of these tracks in microtubule regrowth is discussed.