The actin cytoskeleton operates in a multitude of cellular processes including cell shape and migration, mechanoregulation, and membrane or organelle dynamics. However, its filamentous properties and functions inside the mammalian cell nucleus are less well explored. We previously described transient actin assembly at mitotic exit that promotes nuclear expansion during chromatin decondensation. Here, we identify non‐muscle α‐actinin 4 (ACTN4) as a critical regulator to facilitate F‐actin reorganization and bundling during postmitotic nuclear expansion. ACTN4 binds to nuclear actin filament structures, and ACTN4 clusters associate with nuclear F‐actin in a highly dynamic fashion. ACTN4 but not ACTN1 is required for proper postmitotic nuclear volume expansion, mediated by its actin‐binding domain. Using super‐resolution imaging to quantify actin filament numbers and widths in individual nuclei, we find that ACTN4 is necessary for postmitotic nuclear actin reorganization and actin filament bundling. Our findings uncover a nuclear cytoskeletal function for ACTN4 to control nuclear size and chromatin organization during mitotic cell division.

中文翻译：

---

细胞核的有丝分裂后扩张需要核肌动蛋白丝被α-actinin4束缚。

肌动蛋白的细胞骨架在许多细胞过程中起作用，包括细胞形状和迁移，机械调节以及膜或细胞器动力学。然而，它的丝状特性和在哺乳动物细胞核内部的功能还没有得到很好的研究。我们先前描述了有丝分裂出口处的瞬时肌动蛋白装配，该装配在染色质缩聚过程中促进核扩增。在这里，我们确定非肌肉α-肌动蛋白4（ACTN4）是促进有丝分裂后核扩增过程中F-肌动蛋白重组和束缚的关键调节剂。ACTN4与核肌动蛋白丝结构结合，而ACTN4簇则以高度动态的方式与核F-肌动蛋白结合。由其肌动蛋白结合域介导的适当的有丝分裂后核体积扩增需要ACTN4而不是ACTN1。使用超分辨率成像来量化单个核中肌动蛋白丝的数量和宽度，我们发现ACTN4对于有丝分裂后核肌动蛋白重组和肌动蛋白丝束捆绑是必需的。我们的发现揭示了ACTN4的核细胞骨架功能，以控制有丝分裂细胞分裂过程中的核大小和染色质组织。