Nondisjunction in <i>mad</i> mutants.

Mitosis and meiosis have two mechanisms for regulating the accuracy of chromosome segregation: error correction and the spindle assembly checkpoint (SAC). We have investigated the function of several checkpoint proteins in meiosis I of Drosophila oocytes. Increased localization of several SAC proteins was found upon depolymerization of microtubules by colchicine. However, unattached kinetochores or errors in biorientation of homologous chromosomes do not induce increased SAC protein localization. Furthermore, the metaphase I arrest does not depend on SAC genes, suggesting the APC is inhibited even if the SAC is not functional. Two SAC proteins, ROD of the ROD-ZW10-Zwilch (RZZ) complex and MPS1, are also required for the biorientation of homologous chromosomes during meiosis I, suggesting an error correction function. Both proteins aid in preventing or correcting erroneous attachments and depend on SPC105R for localization to the kinetochore. We have defined a region of SPC105R, amino acids 123–473, that is required for ROD localization and biorientation of homologous chromosomes at meiosis I. Surprisingly, ROD removal from kinetochores and movement towards spindle poles, termed “streaming,” is independent of the dynein adaptor Spindly and is not linked to the stabilization of end-on attachments. Instead, meiotic RZZ streaming appears to depend on cell cycle stage and may be regulated independently of kinetochore attachment or biorientation status. We also show that Spindly is required for biorientation at meiosis I, and surprisingly, the direction of RZZ streaming.有丝分裂与减数分裂存在两种调控染色体分离准确性的机制：错误校正与纺锤体组装检验点（spindle assembly checkpoint, SAC）。我们针对果蝇卵母细胞减数分裂I过程中的多种检验点蛋白功能展开了研究。经秋水仙素解聚微管后，可观察到多种SAC蛋白的定位水平升高。然而，未附着动粒或同源染色体双极定向异常均无法诱导SAC蛋白定位上调。此外，减数分裂I中期阻滞并不依赖于SAC基因，这提示即便SAC功能丧失，后期促进复合物（Anaphase Promoting Complex, APC）仍会受到抑制。两种SAC蛋白——ROD-ZW10-Zwilch（RZZ）复合物中的ROD以及MPS1，同时在减数分裂I的同源染色体双极定向过程中发挥功能，表明二者具备错误校正作用。这两种蛋白均可协助阻止或纠正错误的附着状态，且其在动粒上的定位依赖于SPC105R。我们明确了SPC105R上123至473位氨基酸区域是ROD定位以及减数分裂I时期同源染色体双极定向所必需的。令人意外的是，ROD从动粒脱离并向纺锤体极移动的过程（被称为"streaming（流散）"）并不依赖于动力蛋白适配因子Spindly，且与端附着的稳定化无关。相反，减数分裂过程中的RZZ流散似乎依赖于细胞周期时相，且可能独立于动粒附着状态或双极定向状态受到调控。我们还证实，Spindly是减数分裂I时期同源染色体双极定向所必需的，同时也会影响ROD流散的方向。