Xenbase Image ID: 125627

Figure 3. Spindle assembly is sensitive to mechanisms affecting internal MT organization but not to MT length distribution. (A) When the area of chromatin-mediated nucleation was decreased to span 10 µm, the bipolarity (green, yellow, and red) of MT structures was sensitive to the nucleation pathway. Color indicates MT ”bipolarity index” defined in Materials and methods: astral (red), bipolar (yellow), strongly bipolar (green). MT structures remained bipolar only for percentages of chromatin-mediated nucleation up to 25%, while spindle length in the bipolar regime scaled slightly with nucleation pathway (92 simulations). (B) Position of the minus ends of right-oriented MTs at a single time point with a 10-µm zone of chromatin-mediated MT nucleation (double arrow). In a simulation with 86% MT amplification (green), the bipolar MT structure contained short MTs throughout while long MTs were positioned with their minus ends at the pole (dashed lines). Four sample MTs are illustrated (arrows). In a simulation with only 25% MT amplification (red), the astral MT structure also contained small MTs throughout, but minus ends did not extend far from the midzone, and plus ends grew past minus ends. (C) Mean MT length and bipolarity index (color) for simulations in which parameters for the nucleation pathway, MT plus-end growth rate, MT plus-end catastrophe rate, and kinesin-13 rate were varied. Bold circles indicate the simulations represented in D (92, 99, 95, 99 simulations). (D) Total MT density along the pole-to-pole axis from representative simulations (bold circles in C), where color indicates bipolarity index. Spindles could form and fail in a variety of sizes, indicating a strong dependence for bipolarity on assembly mechanism rather than the exact organization of the MT structure. Image published in: Loughlin R et al. (2010) © 2010 Loughlin et al. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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