The building of nuclear bodies after mitosis is a coordinated event crucial for nuclear organization and function. The nucleolus is assembled during early G(1) phase. Here, two periods (early G1a and early G1b) have been defined. During these periods, the nucleolar compartments (DFC, GC) corresponding to different steps of ribosome biogenesis are progressively assembled. In telophase, rDNA transcription is first activated and PNBs (reservoirs of nucleolar processing proteins) are formed. The traffic of the processing proteins between incipient nucleoli and PNBs was analyzed using photoactivation. We demonstrate that the DFC protein fibrillarin passes from one incipient nucleolus to other nucleoli but not to PNBs, and that the GC proteins, B23/NPM and Nop52, shuttle between PNBs and incipient nucleoli. This difference in traffic suggests a way of regulating assembly first of DFC and then of GC. The time of residency of GC proteins is high in incipient nucleoli compared to interphase nuclei, it decreases in LMB-treated early G1a cells impairing the assembly of GC. Because the assembly of the nucleolus and that of the Cajal body at the exit from mitosis are both sensitive to CRM1 activity, we discuss the fact that assembly of GC and/or its interaction with DFC in early G1a depends on shuttling between PNBs and NORs in a manner dependent on Cajal body assembly.

中文翻译：

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核仁组织区和核前体之间的蛋白质运输控制着有丝分裂出口处核仁的组装

有丝分裂后核体的构建是对核组织和功能至关重要的协调事件。核仁是在早期 G(1) 阶段组装的。这里定义了两个时期（早 G1a 和早 G1b）。在这些时期，与核糖体生物合成的不同步骤相对应的核仁区室（DFC、GC）逐渐组装。在末期，rDNA 转录首先被激活并形成 PNB（核仁加工蛋白的库）。使用光活化分析初始核仁和 PNB 之间加工蛋白质的流量。我们证明 DFC 蛋白原纤蛋白从一个初始核仁传递到另一个核仁，但不传递到 PNB，并且 GC 蛋白 B23/NPM 和 Nop52 在 PNB 和初始核仁之间穿梭。流量的这种差异表明了一种首先调节 DFC 然后调节 GC 的组装方式。与间期细胞核相比，GC 蛋白在初始核仁中的驻留时间较长，在 LMB 处理的早期 G1a 细胞中它会减少，从而损害 GC 的组装。因为有丝分裂出口处核仁的组装和 Cajal 体的组装都对 CRM1 活性敏感，我们讨论了这样一个事实，即 G1a 早期 GC 的组装和/或其与 DFC 的相互作用取决于 PNB 和 NOR 之间的穿梭一种依赖于 Cajal 车身组装的方式。