Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL.
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL.
J Cell Biol. 2020 Jan 6;219(1). doi: 10.1083/jcb.201904046.
Many active genes reproducibly position near nuclear speckles, but the functional significance of this positioning is unknown. Here we show that HSPA1B BAC transgenes and endogenous Hsp70 genes turn on 2-4 min after heat shock (HS), irrespective of their distance to speckles. However, both total HSPA1B mRNA counts and nascent transcript levels measured adjacent to the transgene are approximately twofold higher for speckle-associated alleles 15 min after HS. Nascent transcript level fold-increases for speckle-associated alleles are 12-56-fold and 3-7-fold higher 1-2 h after HS for HSPA1B transgenes and endogenous genes, respectively. Severalfold higher nascent transcript levels for several Hsp70 flanking genes also correlate with speckle association at 37°C. Live-cell imaging reveals that HSPA1B nascent transcript levels increase/decrease with speckle association/disassociation. Initial investigation reveals that increased nascent transcript levels accompanying speckle association correlate with reduced exosome RNA degradation and larger Ser2p CTD-modified RNA polymerase II foci. Our results demonstrate stochastic gene expression dependent on positioning relative to a liquid-droplet nuclear compartment through "gene expression amplification."
许多活跃的基因可重复地定位在核斑点附近，但这种定位的功能意义尚不清楚。在这里，我们表明 HSPA1B BAC 转基因和内源性 Hsp70 基因在热休克（HS）后 2-4 分钟内打开，而与它们与斑点的距离无关。然而，HS 后 15 分钟，与斑点相关的等位基因的 HSPA1B 总 mRNA 计数和新生转录本水平测量值分别约为两倍。HS 后 1-2 小时，与斑点相关的等位基因的新生转录本水平增加倍数分别为 HSPA1B 转基因和内源性基因的 12-56 倍和 3-7 倍。几个 Hsp70 侧翼基因的新生转录本水平也高出几倍，与 37°C 时的斑点相关。活细胞成像显示，HSPA1B 新生转录本水平随斑点的关联/分离而增加/减少。初步研究表明，与斑点相关的新生转录本水平升高与外泌体 RNA 降解减少和 Ser2p CTD 修饰的 RNA 聚合酶 II 焦点增大有关。我们的结果表明，依赖于相对液滴状核区室的定位的随机基因表达通过“基因表达放大”来实现。
