Increase in chromatid length is associated with cell elongation during anaphase/telophase. (a) Still images from time-lapse movies of individual neuroblasts expressing the H2Av::RFP (red) during late cytokinesis. The top row shows the histone variant H2Av fused with RFP (H2Av::RFP) images (red), and the bottom row shows differential interference contrast (DIC) images merged with H2Av::RFP signal (red). All images are oriented with the GMC at the top. The cyan arrows indicate the position of the tip of the longest chromatids lagging behind the mass of chromatids. The gray and white broken lines outline the cells. Asterisks designate cell blebs. Bars, 8 µm. (b) Schemes indicating how the various lengths, widths, and distances were measured for graphs c–f in live cells (see Materials and methods). (c) Scatter dot plot with mean ± SD showing the range of the longest chromatid length in the GMC (GMC LCL) for control and I-CreI cells. (d) Scatter dot plot with mean ± SD showing the GMC elongation index for control and I-CreI cells. (e) Scatter dot plot with mean ± SD showing the neuroblast (N) elongation index for control and I-CreI cells. (f) Graph showing the linear correlation (R2 = 0.6) of the GMC elongation index with the longest chromatid length for I-CreI cells. (g) Time-lapse images of control and I-CreI neuroblasts expressing H2Av::RFP (red). Each image is one sagittal DIC image merged with the H2Av::RFP signal. The cyan arrows indicate the positions of the tip of the longest chromatids. The white broken lines outline the cells. Time is given in minutes. 0 = anaphase onset. The top row shows a control cell (see Video 1). The middle row shows a cell with I-CreI–induced long chromatids that elongates and starts rounding up 7 min after anaphase onset in parallel with the decrease in chromatid arm length (see Video 2). The third row shows a cell with long chromatids that takes longer to round up. The cell stays elongated until 12 min after anaphase onset before starting to round up (see Video 3). Bars, 8 µm. (h) Graph showing the GMC elongation index (mean ± SD) over time for control and I-CreI cells exhibiting long chromatids. Time starts at anaphase onset. (i) Scatter dot plot with mean ± SD showing the diameter of the GMC at the end of mitosis relative to the neuroblast diameter for control and I-CreI cells. n = number of cells.
