RNA transcription modulates phase transition-driven nuclear body assembly
RNA transcription modulates phase transition-driven nuclear body assembly
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DOI：
10.1073/pnas.1509317112
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发表时间：
2015-09-22
影响因子：
11.1
通讯作者：
Brangwynne, Clifford P.
中科院分区：
文献类型：
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作者：
Berry, Joel;Weber, Stephanie C.;Brangwynne, Clifford P.
核体是富含RNA和蛋白质的无膜细胞器，在基因调控中发挥重要作用。最大和最著名的核体是核仁，它是一种细胞器，其在核糖体生物发生中的主要功能使其成为细胞生长和大小稳态的关键。核仁和其他核体的行为类似于液相液滴，似乎是通过浓度依赖性相分离从核质中浓缩而成。然而，核仁积极消耗化学能，目前还不清楚这种非平衡活动如何影响经典的液-液相分离。在这里，我们结合联合收割机在体内和体外实验与理论和模拟来表征核仁的组装和拆卸动力学在秀丽隐杆线虫早期胚胎。除了在转录活性核仁组织区组装的经典核仁外，我们还观察到数十个以不依赖于转录的方式在核质中凝聚的“核仁液滴”（ENDS）。我们发现，增长的核仁和ENDS是一致的一阶相变中，后期粗化动力学介导的布朗聚结，并在较小程度上，奥斯特瓦尔德熟化。通过操纵C. elegans细胞大小，我们改变核仁组分浓度，并确认几个关键模型的预测。我们的研究结果表明，rRNA转录和其他非平衡生物活性可以调节有效的热力学参数控制核仁和END组装，但没有出现从根本上改变被动相分离机制。
Nuclear bodies are RNA and protein-rich, membraneless organelles that play important roles in gene regulation. The largest and most well-known nuclear body is the nucleolus, an organelle whose primary function in ribosome biogenesis makes it key for cell growth and size homeostasis. The nucleolus and other nuclear bodies behave like liquid-phase droplets and appear to condense from the nucleoplasm by concentration-dependent phase separation. However, nucleoli actively consume chemical energy, and it is unclear how such nonequilibrium activity might impact classical liquid-liquid phase separation. Here, we combine in vivo and in vitro experiments with theory and simulation to characterize the assembly and disassembly dynamics of nucleoli in early Caenorhabditis elegans embryos. In addition to classical nucleoli that assemble at the transcriptionally active nucleolar organizing regions, we observe dozens of "extranucleolar droplets" (ENDs) that condense in the nucleoplasm in a transcription-independent manner. We show that growth of nucleoli and ENDs is consistent with a first-order phase transition in which late-stage coarsening dynamics are mediated by Brownian coalescence and, to a lesser degree, Ostwald ripening. By manipulating C. elegans cell size, we change nucleolar component concentration and confirm several key model predictions. Our results show that rRNA transcription and other nonequilibrium biological activity can modulate the effective thermodynamic parameters governing nucleolar and END assembly, but do not appear to fundamentally alter the passive phase separation mechanism.