Carter K C, Taneja K L, Lawrence J B
Department of Cell Biology, University of Massachusetts Medical Center, Worcester 01655.
J Cell Biol. 1991 Dec;115(5):1191-202. doi: 10.1083/jcb.115.5.1191.
The functional organization of the nucleus was studied using a fluorescence microscopy approach which allowed integration of positional information for RNA, DNA, and proteins. In cells from sea urchin to human, nuclear poly(A) RNA was found concentrated primarily within several discrete "transcript domains" which often surrounded nucleoli. Concentrations of poly(A) RNA were coincident with snRNP antigen clusters, providing evidence for the localization of pre-mRNA splicing at these sites. The spatial relationship of transcript domains with respect to various classes of DNA was established, in that the poly(A) RNA-rich regions coincided with discrete regions of low DNA density and were non-randomly distributed with respect to specific DNA sequences. Centromeric DNA and late-replicating DNA did not overlap transcript domains, whereas a subset of early-replicating DNA may. Results indicate that transcript domains do not result directly from a simple clustering of chromatin corresponding to metaphase chromosomes bands. Finally, observations on the reassembly of these domains after mitosis suggest that the clustering of snRNP antigens may be dependent on the reappearance of pol II transcription. Implications of these findings for overall nuclear structure and function are considered, including a discussion of whether transcript domains may be sites of polymerase II transcription reflecting a clustering of active genes.
利用荧光显微镜技术研究了细胞核的功能组织，该技术能够整合RNA、DNA和蛋白质的位置信息。在从海胆到人类的细胞中，发现核聚腺苷酸RNA主要集中在几个离散的“转录结构域”内，这些结构域常常围绕着核仁。聚腺苷酸RNA的聚集与小核核糖核蛋白抗原簇重合，为前体mRNA剪接在这些位点的定位提供了证据。确定了转录结构域与各类DNA的空间关系，富含聚腺苷酸RNA的区域与低DNA密度的离散区域重合，并且相对于特定DNA序列呈非随机分布。着丝粒DNA和晚期复制DNA不与转录结构域重叠，而一部分早期复制DNA可能重叠。结果表明，转录结构域并非直接由对应于中期染色体带的染色质简单聚集产生。最后，对有丝分裂后这些结构域重新组装的观察表明，小核核糖核蛋白抗原的聚集可能依赖于聚合酶II转录的重新出现。考虑了这些发现对整体核结构和功能的影响，包括讨论转录结构域是否可能是反映活性基因聚集的聚合酶II转录位点。
