Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637, USA.
J Cell Sci. 2017 Dec 15;130(24):4180-4192. doi: 10.1242/jcs.206854. Epub 2017 Nov 13.
Nuclear speckles are self-assembled organelles composed of RNAs and proteins. They are proposed to act as structural domains that control distinct steps in gene expression, including transcription, splicing and mRNA export. Earlier studies identified differential localization of a few components within the speckles. It was speculated that the spatial organization of speckle components might contribute directly to the order of operations that coordinate distinct processes. Here, by performing multi-color structured illumination microscopy, we characterized the multilayer organization of speckles at a higher resolution. We found that SON and SC35 (also known as SRSF2) localize to the central region of the speckle, whereas and small nuclear (sn)RNAs are enriched at the speckle periphery. Coarse-grained simulations indicate that the non-random organization arises due to the interplay between favorable sequence-encoded intermolecular interactions of speckle-resident proteins and RNAs. Finally, we observe positive correlation between the total amount of RNA present within a speckle and the speckle size. These results imply that speckle size may be regulated to accommodate RNA accumulation and processing. Accumulation of RNA from various actively transcribed speckle-associated genes could contribute to the observed speckle size variations within a single cell.
核斑点是由 RNA 和蛋白质组成的自组装细胞器。它们被认为是控制基因表达不同步骤的结构域，包括转录、剪接和 mRNA 输出。早期的研究确定了斑点内少数成分的差异定位。有人推测，斑点成分的空间组织可能直接有助于协调不同过程的操作顺序。在这里，通过进行多色结构光照显微镜，我们以更高的分辨率表征了斑点的多层组织。我们发现 SON 和 SC35（也称为 SRSF2）定位于斑点的中心区域，而 和小核（sn）RNAs 在斑点外围富集。粗粒度模拟表明，非随机组织的出现是由于斑点驻留蛋白和 RNA 之间有利的序列编码的分子间相互作用的相互作用。最后，我们观察到斑点内存在的 RNA 总量与斑点大小之间存在正相关。这些结果表明，斑点大小可能受到调节以适应 RNA 积累和加工。来自各种活跃转录的斑点相关基因的 RNA 的积累可能导致单个细胞内观察到的斑点大小变化。
