Janevski J, Park P C, De Boni U
Department of Physiology, Faculty of Medicine, University of Toronto, Ontario, Canada.
Exp Cell Res. 1995 Apr;217(2):227-39. doi: 10.1006/excr.1995.1082.
The existence of a function-dependent, nonrandom organization of chromatin domains within interphase nuclei is supported by evidence which suggests that specific chromatin domains undergo spatial rearrangement under conditions which alter gene expression. Exposure to estrogen of male Xenopus laevis hepatocytes in vitro results in de novo activation of vitellogenin mRNA production and vitellogenin protein synthesis and provides an ideal model to study the association between chromatin organization and changes in gene expression. In a test of the hypothesis that the de novo induction of vitellogenesis in male X. laevis is associated with a spatial rearrangement of specific chromatin domains, centromeric regions were localized by immunofluorescent labeling of associated kinetochore proteins in naive and in estrogen-treated, vitellogenic cells. Analyses by confocal scanning laser microscopy of the three-dimensional spatial distribution of kinetochores in estrogen-treated male hepatocytes showed that a significantly greater proportion of signals was associated with the nuclear periphery than in non-estrogen-treated, naive male cells. In hepatocyte nuclei, quantification of kinetochore signal sizes using image analysis showed that these signals were fewer in number and showed greater variation in size than those of cells in metaphase, with larger signals exhibiting total normalized fluorescence intensities of two, three, four, and five times that associated with kinetochore signals of metaphase cells. These observations are taken to reflect the existence of clustering of kinetochores and, by extension, of centromeres in these cells. In summary, the results show that centromeric domains within interphase nuclei of Xenopus hepatocytes occur as clusters and that these domains undergo spatial rearrangement under conditions which alter the transcriptional state of the cell.
有证据支持间期核内染色质结构域存在功能依赖的非随机组织，这表明在改变基因表达的条件下，特定染色质结构域会发生空间重排。体外将雄性非洲爪蟾肝细胞暴露于雌激素中，会导致卵黄蛋白原mRNA产生和卵黄蛋白原蛋白合成的从头激活，并为研究染色质组织与基因表达变化之间的关联提供了理想模型。在一项关于雄性非洲爪蟾卵黄生成的从头诱导与特定染色质结构域的空间重排相关的假说测试中，通过对未处理和雌激素处理的、处于卵黄生成状态的细胞中相关动粒蛋白进行免疫荧光标记，定位了着丝粒区域。通过共聚焦扫描激光显微镜对雌激素处理的雄性肝细胞中动粒的三维空间分布进行分析，结果显示，与未用雌激素处理的未成熟雄性细胞相比，与核周边相关的信号比例显著更高。在肝细胞核中，使用图像分析对着丝粒信号大小进行定量分析，结果表明，这些信号的数量比中期细胞中的信号少，且大小变化更大，较大信号的总归一化荧光强度是中期细胞着丝粒信号的两倍、三倍、四倍和五倍。这些观察结果被认为反映了这些细胞中动粒的聚集情况，进而反映了着丝粒的聚集情况。总之，结果表明非洲爪蟾肝细胞间期核内的着丝粒结构域以簇的形式存在，并且这些结构域在改变细胞转录状态的条件下会发生空间重排。
