Transcriptional activity generates chromatin motion that drives nuclear blebbing

Abnormal nuclear blebbing is a hallmark of human diseases, including cancers and age-related disorders. Previous work has outlined that nuclear blebbing is due to an imbalance of nuclear strength resisting actin confinement and contraction. Independent of this balance, our recent work revealed that inhibiting RNA polymerase II (RNA Pol II) suppresses nuclear blebbing, but the mechanism remains unknown. Disruption of transcriptional activity through rapid degradation of RNA Pol II via auxin inducible degron suppresses nuclear blebbing. To more finely decrease then restore transcriptional activity, we removed culture media serum and then added it back respectively. Decreasing transcriptional activity decreases nuclear bleb formation, stability, and rupture while returning transcriptional activity increases nuclear blebbing. These modulations of transcriptional activity did not alter the nuclear spring constant or actin confinement and contraction. Instead, we find that transcriptional activity regulates chromatin domain motion measured by mean square displacement (MSD) of chromatin domains labeled via transfected Cy3-dNTPs. Increasing chromatin domain motion using an established RAD51 inhibitor B02 resulted in increased nuclear blebbing. Thus, we reveal that transcriptional activity drives nuclear blebbing through chromatin motion.核膜出泡异常是人类多种疾病的标志性特征，涵盖癌症与年龄相关性病症。既往研究已阐明，核膜出泡源于细胞核抗肌动蛋白约束与收缩的强度失衡。本团队近期的独立研究发现，抑制RNA聚合酶II（RNA polymerase II，简称RNA Pol II）可抑制核膜出泡，但具体机制尚未明确。通过生长素诱导降解标签（auxin inducible degron）快速降解RNA聚合酶II以破坏转录活性，可有效抑制核膜出泡。为实现转录活性的精细化降低与恢复，我们分别移除培养基血清后再将其回补。实验结果显示，降低转录活性可减少核膜出泡的形成、稳定性与破裂事件，而恢复转录活性则会增加核膜出泡的发生。这类转录活性的调控并未改变细胞核的弹性常数，亦未影响肌动蛋白的约束与收缩作用。相反，我们发现转录活性可调控染色质结构域的运动：该运动通过对转染Cy3标记脱氧核苷三磷酸（Cy3-dNTPs）的染色质结构域进行均方位移（mean square displacement, MSD）分析进行量化。使用已报道的RAD51抑制剂B02增强染色质结构域运动后，核膜出泡现象显著增多。综上，本研究揭示转录活性通过调控染色质运动驱动核膜出泡。