Microtubule plus end depolymerization rate is a potentially important target of physiological regulation, but it has been challenging to measure, so its role in spatial organization is poorly understood. Here we apply a method for tracking plus ends based on time difference imaging to measure depolymerization rates in large interphase asters growing in Xenopus egg extract. We observed strong spatial regulation of depolymerization rates, which were higher in the aster interior compared to the periphery, and much less regulation of polymerization or catastrophe rates. We interpret these data in terms of a limiting component model, where aster growth results in lower levels of soluble tubulin and MAPs in the interior cytosol compared to that at the periphery. The steady-state polymer fraction of tubulin was ∼30%, so tubulin is not strongly depleted in the aster interior. We propose that the limiting component for microtubule assembly is a MAP that inhibits depolymerization, and that egg asters are tuned to low microtubule density.

微管加末端解聚率是生理调节的一个潜在的重要目标，但测量起来具有挑战性，因此对其在空间组织中的作用知之甚少。在这里，我们应用一种基于时间差成像的跟踪加端的方法来测量在非洲爪蟾中生长的大型间期紫菀的解聚率 鸡蛋提取物。我们观察到解聚速率的强烈空间调节，与外围相比，翠菊内部的解聚速率更高，而聚合或灾难速率的调节则要少得多。我们根据限制成分模型来解释这些数据，其中紫菀生长导致内部细胞质溶胶中可溶性微管蛋白和 MAP 的水平低于外围。微管蛋白的稳态聚合物分数约为 30%，因此微管蛋白在紫菀内部没有强烈消耗。我们建议微管组装的限制成分是抑制解聚的 MAP，并且将蛋紫调节为低微管密度。