Fig. 4. Short dynamic microtubules are part of the early spindle. (A) INA microtubules appear at the earliest stages of spindle assembly. These still images are projections of three 0.4µm sections taken at 7-second intervals (strain, YY105). The fluorescent bar is the short spindle. The arrow at time point 35 shows the earliest detected INA microtubule before any visible spindle pole separation has occurred. The arrow at time 56 shows the same INA microtubule that has elongated towards the nuclear center. The arrow at time 119 shows two INA microtubules after spindle pole separation, one extending from each spindle pole. Bar, 1 µm (see Movie 2, http://jcs.biologists.org/supplemental/). (B) Sequential images of a single nucleus with an early phase 1 spindle and INA microtubules taken at approximately 2-second intervals. The arrows follow a single INA microtubule bundle as it sweeps across the nucleus. The same microtubule stops sweeping and appears to grow in length over the next several time frames. The cells in both A and B progressed normally through anaphase. Bar, 1 µm (see Movie 3, http://jcs.biologists.org/supplemental/).