Skibbens R V, Salmon E D
Department of Biology, University of North Carolina, Chapel Hill 27599-3280, USA.
Exp Cell Res. 1997 Sep 15;235(2):314-24. doi: 10.1006/excr.1997.3691.
In mitotic vertebrate tissue cells, chromosome congression to the spindle equator in prometaphase and segregation to the poles in anaphase depend on the movements ofkinetochores at their kinetochore microtubule attachment sites. To test if kinetochores sense tension to control their states of movement poleward (P) and away from the pole (AP), we applied an external force to the spindle in preanaphase newt epithelial cells by stretching chromosome arms with microneedles. For monooriented chromosomes (only one kinetochore fiber), an abrupt stretch of an arm away from the attached pole induced the single attached kinetochore to persist in AP movement at about 2 microm/min velocity, resulting in chromosome movement away from the pole. When the stretch was reduced or the needle removed, the kinetochore switched to P movement at about 2 microm/min and pulled the chromosome back to near the premanipulation position within the spindle. For bioriented chromosomes (sister kinetochores attached to opposite poles) near the spindle equator, stretching one arm toward a pole placed the kinetochore facing away from the direction of stretch under tension and the sister facing toward the stretch under reduced tension or compression. Kinetochores under increased tension exhibited prolonged AP movement while kinetochores under reduced tension or compression exhibited prolonged P movement, moving the centromeres at about 2 microm/min velocities off the metaphase plate in the direction of stretch. Removing the needle resulted in centromere movement back to near the spindle equator at similar velocities. These results show that tension controls the direction of kinetochore movement and associated kinetochore microtubule assembly/disassembly to position centromeres within the spindle of vertebrate tissue cells. High tension induces persistent AP movement while low tension induces persistent P movement. The velocity of P and AP movement appears to be load independent and governed by the molecular mechanisms which attach kinetochores to the dynamic ends of kinetochore microtubules.
在有丝分裂的脊椎动物组织细胞中，前中期染色体向纺锤体赤道板汇聚以及后期向两极分离，依赖于动粒在其动粒微管附着位点的运动。为了测试动粒是否感知张力以控制其向极（P）和远离极（AP）的运动状态，我们在蝾螈上皮细胞的前后期，通过用微针拉伸染色体臂，对纺锤体施加外力。对于单定向染色体（只有一条动粒纤维），将一条臂突然从附着的极拉伸开，会诱导单个附着的动粒以约2微米/分钟的速度持续进行AP运动，导致染色体远离极移动。当拉伸减小或移开针时，动粒会切换为以约2微米/分钟的速度进行P运动，并将染色体拉回到纺锤体内接近操作前的位置。对于靠近纺锤体赤道板的双定向染色体（姐妹动粒附着于相反两极），向一极拉伸一条臂会使远离拉伸方向的动粒处于张力之下，而姐妹动粒处于减小的张力或压缩之下。张力增加的动粒表现出延长的AP运动，而张力减小或受到压缩的动粒表现出延长的P运动，着丝粒以约2微米/分钟的速度沿拉伸方向从中期板移开。移开针会导致着丝粒以相似速度回到接近纺锤体赤道板的位置。这些结果表明，张力控制动粒运动方向以及相关的动粒微管组装/拆卸，从而在脊椎动物组织细胞的纺锤体内定位着丝粒。高张力诱导持续的AP运动，而低张力诱导持续的P运动。P和AP运动的速度似乎与负载无关，由将动粒附着到动粒微管动态末端的分子机制控制。
