Maloriented bivalents have metaphase positions at the spindle equator with more kinetochore microtubules to one pole than to the other
Maloriented bivalents have metaphase positions at the spindle equator with more kinetochore microtubules to one pole than to the other
复制标题
有向性的二价体位于纺锤体赤道的分裂期位置，一极的动点小管比另一极的多
DOI：
10.1091/mbc.e04-06-0524
复制
发表时间：
2004-12-01
影响因子：
3.3
通讯作者：
Oldenbourg, R
中科院分区：
文献类型：
--
作者：
LaFountain, JR;Oldenbourg, R
为了验证二价体减数分裂中期定位的“牵引纤维”模型，用液晶偏光显微镜分析了冷停滞恢复过程中诱导的取向不良的二价体动粒纤维。动粒纤维的双折射延迟与纤维中微管的数量成正比。在所分析的11种取向不良的二价体中，有5种表现出双极取向不良，其中一极的动粒微管至少是另一极的四倍，两个微管只指向一极。然而，所有取向不良的二价体都位于纺锤形赤道或其附近。牵引纤维模型预测，这种取向不良的二价体应该放置在更靠近极点的位置，有更多的动粒微管。根据该模型，在纺锤体赤道的中期位置，两极需要相同数量的动粒微管。偏光显微镜图像的数据与这些预测不一致，从而得出结论，除了牵引力之外，其他因素肯定参与了鹤-蝇精母细胞的中期定位。虽然其他因素的一致性尚未确定，但一种可能性是，极地弹射力的作用是施加远离极点的力，这可能会抵消极点方向的牵引力。另一种说法是，动感神经是“智能的”，这意味着它们体现了一种位置敏感的机制，可以控制它们的活动。
To test the "traction fiber" model for metaphase positioning of bivalents during meiosis, kinetochore fibers of maloriented bivalents, induced during recovery from cold arrest, were analyzed with a liquid crystal polarizing microscope. The measured birefringence retardation of kinetochore fibers is proportional to the number of microtubules in a fiber. Five of the 11 maloriented bivalents analyzed exhibited bipolar malorientations that had at least four times more kinetochore microtubules to one pole than to the other pole, and two had microtubules directed to only one pole. Yet all maloriented bivalents had positions at or near the spindle equator. The traction fiber model predicts such maloriented bivalents should be positioned closer to the pole with more kinetochore microtubules. A metaphase position at the spindle equator, according to the model, requires equal numbers of kinetochore microtubules to both poles. Data from polarizing microscope images were not in accord with those predictions, leading to the conclusion that other factors, in addition to traction forces, must be involved in metaphase positioning in crane-fly spermatocytes. Although the identity of additional factors has not been established, one possibility is that polar ejection forces operate to exert away-from-the-pole forces that could counteract pole-directed traction forces. Another is that kinetochores are "smart," meaning they embody a position-sensitive mechanism that controls their activity.