Khanna Nimish, Hu Yan, Belmont Andrew S
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Curr Biol. 2014 May 19;24(10):1138-44. doi: 10.1016/j.cub.2014.03.053. Epub 2014 May 1.
Association and disassociation of gene loci with respect to specific nuclear compartments accompany changes in gene expression, yet little is known concerning the mechanisms by which this occurs or its functional consequences. Previously, we showed that tethering acidic activators to a peripheral chromosome site led to movement of the chromosome site away from the nuclear periphery, but the physiological relevance of this movement was unclear [1]. Nuclear speckles, or interchromatin granule clusters, are enriched in factors involved in RNA processing [2], and the association of a subset of active genes at their periphery suggests speckles may play a role in gene expression [3, 4]. Here, we show an actin-dependent association of HSP70 transgenes with nuclear speckles after heat shock. We visualized HSP70 transgenes moving curvilinearly toward nuclear speckles over ∼0.5-6 μm distances at velocities of 1-2 μm min(-1). Chromatin stretching in the direction of movement demonstrates a force-generating mechanism. Transcription in nearly all cases increased noticeably only after initial contact with a nuclear speckle. Moreover, blocking new HSP70 transgene/speckle association by actin depolymerization prevented significant heat shock-induced transcriptional activation in transgenes not associated with speckles, although robust transcriptional activation was observed for HSP70 transgenes associated with nuclear speckles. Our results demonstrate the existence of a still-to-be-revealed machinery for moving chromatin in a direct path over long distances toward nuclear speckles in response to transcriptional activation; moreover, this speckle association enhances the heat shock activation of these HSP70 transgenes.
基因座与特定核区室的缔合和解离伴随着基因表达的变化，然而对于其发生机制或功能后果却知之甚少。此前，我们发现将酸性激活剂拴系到外周染色体位点会导致该染色体位点从核边缘移开，但这种移动的生理相关性尚不清楚[1]。核斑点或染色质间颗粒簇富含参与RNA加工的因子[2]，并且一些活跃基因在其外周的缔合表明斑点可能在基因表达中起作用[3,4]。在这里，我们展示了热休克后HSP70转基因与核斑点的肌动蛋白依赖性缔合。我们观察到HSP70转基因以1 - 2μm min(-1)的速度在约0.5 - 6μm的距离上沿曲线向核斑点移动。在移动方向上的染色质拉伸证明了一种产生力的机制。几乎在所有情况下，转录仅在最初与核斑点接触后才显著增加。此外，通过肌动蛋白解聚阻断新的HSP70转基因/斑点缔合可防止未与斑点缔合的转基因中显著的热休克诱导的转录激活，尽管与核斑点缔合的HSP70转基因观察到了强大的转录激活。我们的结果表明存在一种尚未揭示的机制，可响应转录激活使染色质沿直接路径长距离向核斑点移动；此外，这种斑点缔合增强了这些HSP70转基因的热休克激活。
