Brown Rae R, Schwartz Jacob P, Ghadri Lyin, Straight Aaron F
Department of Biochemistry, Stanford University School of Medicine.
bioRxiv. 2025 Jul 15:2025.07.15.664882. doi: 10.1101/2025.07.15.664882.
Eukaryotic chromosome segregation requires attachment of chromosomes to microtubules of the mitotic spindle through the kinetochore so that chromosomes can align and move in mitosis. Kinetochores are assembled on the centromere which is a unique chromatin domain that is epigenetically defined by the histone H3 variant CENtromere Protein A (CENP-A). During DNA replication CENP-A is equally divided between replicated chromatids and new CENP-A nucleosomes are re-assembled during the subsequent G1 phase of the cell cycle. How cells regulate the strict cell cycle timing of CENP-A assembly is a central question in the epigenetic maintenance of centromeres and kinetochores. One essential assembly factor for CENP-A nucleosomes is the Mis18 complex (Mis18α, Mis18β, and M18BP1) which is regulated in its localization to centromeres between metaphase and G1 when CENP-A assembly occurs. Here, we define a new regulatory mechanism that works through cell cycle dependent phosphorylation of M18BP1 between metaphase and interphase. This phosphoregulatory switch disrupts binding of M18BP1 to CENP-A nucleosomes in metaphase, and when relieved enables M18BP1 binding to CENP-A nucleosomes in interphase. We show that this phosphorylation dependent switching mechanism regulates CENP-A nucleosome assembly. We propose that the phospho-regulated binding of M18BP1 to CENP-A nucleosomes is an important control mechanism that restricts the timing of new CENP-A assembly.
真核生物染色体分离需要染色体通过动粒附着于有丝分裂纺锤体的微管上，以便染色体在有丝分裂过程中能够排列并移动。动粒组装在着丝粒上，着丝粒是一个独特的染色质结构域，由组蛋白H3变体着丝粒蛋白A（CENP - A）在表观遗传上定义。在DNA复制过程中，CENP - A在复制后的染色单体之间平均分配，并且新的CENP - A核小体在随后的细胞周期G1期重新组装。细胞如何调节CENP - A组装严格的细胞周期时间是着丝粒和动粒表观遗传维持中的一个核心问题。CENP - A核小体的一个重要组装因子是Mis18复合物（Mis18α、Mis18β和M18BP1），其在CENP - A组装发生的中期和G1期之间定位于着丝粒的过程中受到调节。在这里，我们定义了一种新的调节机制，该机制通过中期和间期之间M18BP1的细胞周期依赖性磷酸化起作用。这种磷酸化调节开关在中期破坏M18BP1与CENP - A核小体的结合，而当这种调节解除时，使M18BP1在间期与CENP - A核小体结合。我们表明这种磷酸化依赖性转换机制调节CENP - A核小体组装。我们提出M18BP1与CENP - A核小体的磷酸化调节结合是一种重要的控制机制，可限制新CENP - A组装的时间。
