ANALYSIS AND CONTROL OF CHROMOSOME MOVEMENT

描述（来自申请人摘要的逐字逐句）：目标是了解 精确的染色体运动和染色体的准确分布， 有丝分裂和减数分裂中的子细胞。分配错误可能导致 癌症和唐氏综合症以及人类的其他染色体疾病。细胞如何 避免错误是这个项目的主题。有丝分裂的机械张力 力量是关键。在有丝分裂的早期，染色体移动到一个位置， 正好在主轴两极的中间该机芯由motile 着丝粒（将染色体附着在纺锤体上的结构 微管）。着丝粒在拉动和不活动的“中性”之间切换 状态开关可通过张力进行调节，张力将直接由 用显微操作针推压染色体以放松张力， 允许切换发生。马达动力蛋白和CENP-E存在于 当染色体开始移动，但后来从染色体中丢失时， 染色体这种瞬时动粒马达的可能用途是 测试.染色体分布中常见的错误有两种， 避免这两种情况都涉及紧张。避免第一类错误 依赖于染色体对纺锤体的锚定， 张力两极是敏感地点的可能性将被测试 通过显微操作。第二种错误可以通过检查点来避免 检测错误并延迟有丝分裂的完成。张力敏感 动粒蛋白磷酸化可能是检查点的信号。 张力当然会引起动粒去磷酸化，但其影响可能是 直接（某些组件的变形）或间接（张力增加 微管的数量，这可能导致去磷酸化）。这种模糊性 将通过创造一种可以操纵紧张局势的局面来解决 但不会增加微管的数量。紧张局势对 动粒及其组分的结构将通过结合 显微操作来改变张力，用电子显微镜观察 后果动粒将通过三维重建 断层扫描最终的目标是了解张力，通过改变 结构，可能导致化学变化，如脱磷酸化。

DESCRIPTION (Verbatim from the applicant's abstract): The goal is to understand precise chromosome movement and the accurate distribution of chromosomes to the daughter cells in mitosis and meiosis. Errors in distribution can lead to cancer and to Down syndrome and other chromosome disorders in humans. How cells avoid errors is the subject of this project. Mechanical tension from mitotic forces is the key. Early in mitosis, chromosomes move to a position quite precisely midway between the spindle poles. The movement is powered by motile kinetochores (the structures that attach the chromosome to spindle microtubules). Kinetochores switch between pulling and an inactive, 'neutral' state. The switch may be regulated by tension, which will be tested directly by pushing on chromosomes with a micromanipulation needle to relax the tension and allow switching to occur. The motors dynein and CENP-E are present at kinetochores when chromosomes begin to move but are later lost from the chromosomes. The possible uses for such transitory kinetochore motors will be tested. The common errors in chromosome distribution are of two sorts, and tension is involved in avoiding both of them. Avoiding errors of the first sort depends on an anchorage of chromosomes to the spindle that is sensitive to tension. The possibility that the poles are the sensitive site will be tested by micromanipulation. Errors of the second sort are avoided by a checkpoint that detects errors and delays the completion of mitosis. Tension-sensitive kinetochore protein phosphorylation may be the signal to the checkpoint. Tension certainly causes kinetochore dephosphorylation, but the effect may be direct (deformation of some component) or indirect (tension increases the number of microtubules, which may lead to dephosphorylation). This ambiguity will be resolved by creating a situation in which tension can be manipulated yet does not increase the number of microtubules. The effect of tension on the structure of the kinetochore and its components will be explored by combining micromanipulation to vary the tension force with electron microscopy to view the consequences. Kinetochores will be reconstructed by threedimensional tomography. The ultimate goal is to understand how tension, by altering structure, can lead to chemical changes such as dephosphorylation.