Timely Endocytosis of Cytokinetic Enzymes Prevents Premature Spindle Breakage during Mitotic Exit.
Timely Endocytosis of Cytokinetic Enzymes Prevents Premature Spindle Breakage during Mitotic Exit.
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DOI：
10.1371/journal.pgen.1006195
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发表时间：
2016-07
期刊：
影响因子：
4.5
通讯作者：
Yeong FM
中科院分区：
文献类型：
--
作者：
Chin CF;Tan K;Onishi M;Chew Y;Augustine B;Lee WR;Yeong FM
胞质分裂需要时空协调的膜沉积和初级隔膜（PS）的形成在分裂网站驱动肌动球蛋白环（AMR）的收缩。已经证明AMR收缩总是只发生在有丝分裂纺锤体解体之后。它也已被确定，几丁质合成酶II（Chs 2 p）颈部定位有丝分裂纺锤体解体之前，在有丝分裂出口。由于AMR收缩依赖于PS形成，因此出现了如何调节几丁质沉积以防止过早AMR收缩和有丝分裂纺锤体断裂的问题。在这项研究中，我们提出，细胞调节纺锤体拆卸和AMR收缩之间的协调，通过及时的细胞动力学酶，Chs 2 p，Chs 3 p，和Fks 1 p的内吞作用。内吞作用的抑制导致有丝分裂退出期间细胞动力学酶的过度积累，这加速了AMR的收缩，并导致纺锤体断裂，最终可能有助于在随后的细胞分裂中形成单极纺锤体。有趣的是，在胞吞作用突变体中观察到的有丝分裂纺锤体断裂可以通过缺失或抑制参与隔膜形成的CHS 2、CHS 3和FKS 1的活性来挽救。我们的研究结果强调了在有丝分裂退出过程中，细胞分裂位点细胞动力学酶的及时内吞对维护有丝分裂纺锤体完整性的重要性。在有丝分裂过程中，母细胞-子细胞的物理分离所需的胞质分裂机制从酵母到人类都是高度保守的。在芽殖酵母中，胞质分裂是通过将胞质动力学酶及时递送到最终触发AMR收缩的分裂位点来实现的。以前已经证明，胞质分裂总是发生在有丝分裂纺锤体解体之后。有趣的是，Chs 2 p，这是负责奠定了初级隔膜已被证明是本地化的分裂网站之前，有丝分裂纺锤体解体。在这项研究中，我们表明，有丝分裂纺锤体的完整性后，姐妹染色单体分离是依赖于连续的胞吞作用的细胞动力学酶。有丝分裂退出过程中细胞动力学蛋白内化的失败导致过早的AMR收缩，最终导致有丝分裂纺锤体的剪切。因此，细胞在随后的细胞分裂周期中不能重新建立双极纺锤体。我们的研究结果提供了深入了解分裂位点分泌蛋白的水平如何影响胞质分裂。我们相信，这种调节机制可能是保守的高等真核细胞分泌蛋白，hemicentin，最近已被证明参与调节秀丽隐杆线虫和小鼠胚胎的胞质分裂。
Cytokinesis requires the spatio-temporal coordination of membrane deposition and primary septum (PS) formation at the division site to drive acto-myosin ring (AMR) constriction. It has been demonstrated that AMR constriction invariably occurs only after the mitotic spindle disassembly. It has also been established that Chitin Synthase II (Chs2p) neck localization precedes mitotic spindle disassembly during mitotic exit. As AMR constriction depends upon PS formation, the question arises as to how chitin deposition is regulated so as to prevent premature AMR constriction and mitotic spindle breakage. In this study, we propose that cells regulate the coordination between spindle disassembly and AMR constriction via timely endocytosis of cytokinetic enzymes, Chs2p, Chs3p, and Fks1p. Inhibition of endocytosis leads to over accumulation of cytokinetic enzymes during mitotic exit, which accelerates the constriction of the AMR, and causes spindle breakage that eventually could contribute to monopolar spindle formation in the subsequent round of cell division. Intriguingly, the mitotic spindle breakage observed in endocytosis mutants can be rescued either by deleting or inhibiting the activities of, CHS2, CHS3 and FKS1, which are involved in septum formation. The findings from our study highlight the importance of timely endocytosis of cytokinetic enzymes at the division site in safeguarding mitotic spindle integrity during mitotic exit. The cytokinesis machinery that is required for physical separation of mother-daughter cells during mitosis is highly conserved from yeast to humans. In budding yeast, cytokinesis is achieved via timely delivery of cytokinetic enzymes to the division site that eventually triggers the constriction of AMR. It has been previously demonstrated that cytokinesis invariably occurs after the disassembly of the mitotic spindle. Intriguingly, Chs2p that is responsible for laying down the primary septum has been shown to localize to the division site before mitotic spindle disassembly. In this study, we show that mitotic spindle integrity upon sister chromatid separation is dependent on the continuous endocytosis of cytokinetic enzymes. Failure in the internalization of cytokinetic proteins during mitotic exit causes premature AMR constriction that eventually contributes to the shearing of mitotic spindle. Consequently, cells fail to re-establish a bipolar spindle in the subsequent round of cell division cycle. Our findings provide insights into how the levels of secreted proteins at the division site impacts cytokinesis. We believe this regulation mechanism might be conserved in higher eukaryotic cells as a secreted protein, hemicentin, has been shown recently to be involved in regulating cytokinesis in both Caenorhabditis elegans and mouse embryos.