CRBM, University of Montpellier, CNRS, Montpellier, France.
IGMM, University of Montpellier, CNRS, Montpellier, France.
EMBO Rep. 2020 Jun 4;21(6):e50257. doi: 10.15252/embr.202050257. Epub 2020 Apr 19.
The Mps1 kinase corrects improper kinetochore-microtubule attachments, thereby ensuring chromosome biorientation. Yet, its critical phosphorylation targets in this process remain largely elusive. Mps1 also controls the spindle assembly checkpoint (SAC), which halts chromosome segregation until biorientation is attained. Its role in SAC activation is antagonised by the PP1 phosphatase and involves phosphorylation of the kinetochore scaffold Knl1/Spc105, which in turn recruits the Bub1 kinase to promote assembly of SAC effector complexes. A crucial question is whether error correction and SAC activation are part of a single or separable pathways. Here, we isolate and characterise a new yeast mutant, mps1-3, that is severely defective in chromosome biorientation and SAC signalling. Through an unbiased screen for extragenic suppressors, we found that mutations lowering PP1 levels at Spc105 or forced association of Bub1 with Spc105 reinstate both chromosome biorientation and SAC signalling in mps1-3 cells. Our data argue that a common mechanism based on Knl1/Spc105 phosphorylation is critical for Mps1 function in error correction and SAC signalling, thus supporting the idea that a single sensory apparatus simultaneously elicits both pathways.
Mps1 激酶可以纠正不正确的动粒-微管连接，从而确保染色体的正确定向。然而，其在这个过程中的关键磷酸化靶标在很大程度上仍难以捉摸。Mps1 还控制着纺锤体组装检查点（SAC），该检查点会阻止染色体分离，直到达到正确定向。它在 SAC 激活中的作用被 PP1 磷酸酶拮抗，涉及到动粒支架 Knl1/Spc105 的磷酸化，这反过来又招募了 Bub1 激酶来促进 SAC 效应复合物的组装。一个关键问题是错误修正和 SAC 激活是否属于单一或可分离的途径。在这里，我们分离并表征了一个新的酵母突变体 mps1-3，它在染色体正确定向和 SAC 信号传导方面严重缺陷。通过对附加基因抑制子的无偏筛选，我们发现降低 Spc105 上的 PP1 水平或强制 Bub1 与 Spc105 结合的突变可以恢复 mps1-3 细胞中的染色体正确定向和 SAC 信号传导。我们的数据表明，基于 Knl1/Spc105 磷酸化的共同机制对于 Mps1 在错误修正和 SAC 信号传导中的功能至关重要，因此支持了一个单一的感觉装置同时引发这两种途径的想法。
