Cimini Daniela, Moree Ben, Canman Julie C, Salmon E D
Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
J Cell Sci. 2003 Oct 15;116(Pt 20):4213-25. doi: 10.1242/jcs.00716. Epub 2003 Sep 2.
Merotelic kinetochore orientation is an error that occurs when a single kinetochore becomes attached to microtubules from two spindle poles rather than just to one pole. We obtained the first evidence that merotelic kinetochore orientation occurs very frequently during early mitosis in mammalian tissue cells and that two different correction mechanisms are critical for accurate chromosome segregation in cells possessing bipolar spindles and unperturbed chromosomes. Our data show that about 30% of prometaphase PtK1 cells possess one or more merotelically oriented kinetochores. This frequency is increased to over 90% in cells recovering from a nocodazole-induced mitotic block. A delay in establishing spindle bipolarity is responsible for the high frequency of merotelic orientations seen in cells recovering from nocodazole, but not in untreated cells. The frequency of anaphase cells with merotelically oriented lagging chromosomes is 1% in untreated cells and 18% in cells recovering from nocodazole. Prolonging metaphase by 2 hours reduced the frequency of anaphase cells with lagging chromosomes both for untreated and for nocodazole-treated cells. Surprisingly, anaphase lagging chromosomes represented a very small fraction of merotelic kinetochore orientations present in late metaphase. Our data indicate that two correction mechanisms operate to prevent chromosome missegregation due to merotelic kinetochore orientation. The first, a pre-anaphase correction mechanism increases the ratio of kinetochore microtubules attached to the correct versus incorrect pole and might eventually result in kinetochore reorientation before anaphase onset. The increase in microtubule ratio to opposite poles is the groundwork for a second mechanism, active in anaphase, that promotes the segregation of merotelically oriented chromosomes to the correct pole.
单着丝粒动粒定向是一种错误情况，即单个着丝粒附着于来自两个纺锤体极的微管，而非仅附着于一个纺锤体极。我们首次获得证据表明，在哺乳动物组织细胞的早期有丝分裂过程中，单着丝粒动粒定向非常频繁地发生，并且两种不同的校正机制对于具有双极纺锤体和未受干扰染色体的细胞中染色体的准确分离至关重要。我们的数据显示，约30%的前中期PtK1细胞具有一个或多个单着丝粒定向的动粒。在从诺考达唑诱导的有丝分裂阻滞中恢复的细胞中，这一频率增加到90%以上。纺锤体双极性建立的延迟是从诺考达唑中恢复的细胞中观察到的高频率单着丝粒定向的原因，但在未处理的细胞中并非如此。在未处理的细胞中，具有单着丝粒定向滞后染色体的后期细胞频率为1%，而在从诺考达唑中恢复的细胞中为18%。将中期延长2小时可降低未处理细胞和诺考达唑处理细胞中具有滞后染色体的后期细胞的频率。令人惊讶的是，后期滞后染色体仅占中期后期存在的单着丝粒动粒定向的一小部分。我们的数据表明，两种校正机制发挥作用以防止由于单着丝粒动粒定向导致的染色体错分离。第一种是后期前校正机制，它增加了附着于正确极与错误极的动粒微管的比例，并最终可能导致后期开始前动粒重新定向。微管与相反极比例的增加是第二种机制的基础，该机制在后期活跃，促进单着丝粒定向染色体向正确极的分离。
