Traction force on a kinetochore at metaphase acts as a linear function of kinetochore fiber length.
Traction force on a kinetochore at metaphase acts as a linear function of kinetochore fiber length.
复制标题
DOI：
10.1083/jcb.93.2.374
复制
发表时间：
1982-05
期刊：
影响因子：
--
通讯作者：
Salmon ED
中科院分区：
文献类型：
--
作者：
Hays TS;Wise D;Salmon ED
我们正在研究动粒极向拉力与相应动粒纤维长度之间的关系。Ostergren在1950年认识到，染色体的中期位置可以通过与着丝粒到极点的距离成正比的牵引力来实现。对于典型的染色体(即减数分裂二价体或有丝分裂染色体)，当染色体位于两极之间的中点时，合力(Rf)为零。对于特殊的染色体，其动粒纤维的数量不相等，向相反的两极延伸。对于特殊的染色体，其动粒纤维的数量不相等，向相反的两极延伸。奥斯特格伦提出，对于特殊的染色体，其动粒纤维的数量不相等，向相反的两极延伸，当染色体向更多的动粒纤维拉向的极点移动时，Rf=0。我们通过分析实验产生的具有三个或四个着丝粒纤维的多价染色体的中期位置，测量了活纺锤体中的力-长度关系。用γ辐射不同若虫，产生了不同构型的多价染色体，并分析了它们在第一次减数分裂精子细胞中的行为。动粒纤维的长度是从延时照片中通过测量完全联结的染色体在后期开始之前的动粒到极的距离来确定的。在我们的分析中，沿单个动粒纤维的力(F)表示为：F=kL(Exp)，其中k是与长度无关的比例常数，L表示动粒纤维长度，exp是未知指数。染色体上的Rf由下列公式给出：Rf=σk(I)L(I)(Exp)，其中相对半纺锤体上的动粒纤维长度被赋予相反的符号。如果中期染色体上的力是平衡的(Rf=0)，那么对于多价体的不对称取向，我们可以测量单个动粒纤维的长度(L(I))，并求解产生零合力的指数。该指数的值与沿动粒纤维的力的大小如何随其长度变化有关。对于六个三价态和一个自然生成的四价态，我们计算的平均值为exp=1.06+/-0.18。这一结果与奥斯特格伦的假设一致，并表明沿动粒纤维的极向牵引力的大小与纤维的长度成正比。我们的发现表明，沿动粒纤维的力的平衡可能是调节动粒微管组装程度的主要因素。
We are investigating the relation between the force pulling a kinetochore poleward and the length of the corresponding kinetochore fiber. It was recognized by Ostergren in 1950 (Hereditas 36:1-19) that the metaphase position of a chromosome could be achieved by a balance of traction forces were proportional to the distance from kinetochore to pole. For the typical chromosome (i.e., a meiotic bivalent or mitotic chromosome) with a single kinetochore fiber extending to each pole, the resultant force (RF) would equal zero when the chromosome lay at the midpoint between the two poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles, Ostergren’s proposal suggests that RF = 0 when the chromosome is shifted closer to the pole toward which the greater number of kinetochore fibers are pulling. We have measured the force-length relationship in living spindles by analyzing the metaphase positions of experimentally generated multivalent chromosomes having three or four kinetochore fibers. Multivalent chromosomes of varied configurations were generated by γ-irradiation of nymphs of the grasshopper melanoplus differentialis, and their behavior was analyzed in living first meiotic spermocytes. The lengths of kinetochore fibers were determined from time-lapse photographs by measuring the kinetochore-to-pole distances for fully congressed chromosomes just before the onset of anaphase. In our analysis, force (F) along a single kinetochore fiber is expressed by: F = kL(exp), where k is a length-independent proportionality constant, L represents the kinetochore fiber length, and exp is an unknown exponent. The RF on a chromosome is then given by: RF = σk(i)L(i)(exp), where kinetochore fiber lengths in opposite half- spindles are given opposite sign. If forces on a metaphase chromosome are at equilibrium (RF = 0), then for asymmetrical orientations of multivalents we can measure the individual kinetochore fiber lengths (L(i)) and solve for the exponent that yields a resultant force of zero. The value of the exponent relates how the magnitude of force along a kinetochore fiber varies with its length. For six trivalents and one naturally occurring quadrivalent we calculated an average value of exp = 1.06 +/- 0.18. This result is consistent with Ostergren’s hypothesis and indicates that the magnitude of poleward traction force along a kinetochore fiber is directly proportional to the length of the fiber. Our finding suggests that the balance of forces along a kinetochore fiber may be a major factor regulating the extent of kinetochore microtubule assembly.