Department of Biology, Institute of Biochemistry, ETH Zurich, Zurich, Switzerland.
Molecular Life Sciences Ph.D. Program, Zurich, Switzerland.
EMBO Rep. 2023 Sep 6;24(9):e56766. doi: 10.15252/embr.202356766. Epub 2023 Jul 20.
During mitotic entry of vertebrate cells, nuclear pore complexes (NPCs) are rapidly disintegrated. NPC disassembly is initiated by hyperphosphorylation of linker nucleoporins (Nups), which leads to the dissociation of FG repeat Nups and relaxation of the nuclear permeability barrier. However, less is known about disintegration of the huge nuclear and cytoplasmic rings, which are formed by annular assemblies of Y-complexes that are dissociated from NPCs as intact units. Surprisingly, we observe that Y-complex Nups display slower dissociation kinetics compared with other Nups during in vitro NPC disassembly, indicating a mechanistic difference in the disintegration of Y-based rings. Intriguingly, biochemical experiments reveal that a fraction of Y-complexes remains associated with mitotic ER membranes, supporting recent microscopic observations. Visualization of mitotic Y-complexes by super-resolution microscopy demonstrates that they form two classes of higher order assemblies: large clusters at kinetochores and small, focal ER-associated assemblies. These, however, lack features qualifying them as persisting ring-shaped subassemblies previously proposed to serve as structural templates for NPC reassembly during mitotic exit, which helps to refine current models of nuclear reassembly.
在脊椎动物细胞有丝分裂进入时，核孔复合体（NPC）迅速解体。NPC 的组装是通过连接核孔蛋白（Nups）的过度磷酸化起始的，这导致 FG 重复 Nups 的解离和核通透性屏障的松弛。然而，关于巨大的核质环的解体，人们知之甚少，这些核质环是由从 NPC 作为完整单元解离的 Y 复合物的环形组装形成的。令人惊讶的是，我们观察到，与体外 NPC 解体过程中的其他 Nups 相比，Y 复合物 Nups 的解离动力学较慢，表明 Y 基环解体的机制存在差异。有趣的是，生化实验表明，一部分 Y 复合物仍然与有丝分裂 ER 膜结合，支持最近的显微镜观察。通过超分辨率显微镜对有丝分裂 Y 复合物的可视化表明，它们形成了两类更高阶的组装体：动粒处的大簇和小的、聚焦的 ER 相关组装体。然而，这些组装体缺乏作为 NPC 在有丝分裂退出期间重新组装的结构模板的特征，这有助于完善当前的核重新组装模型。
