Dundr Miroslav, Hebert Michael D, Karpova Tatiana S, Stanek David, Xu Hongzi, Shpargel Karl B, Meier U Thomas, Neugebauer Karla M, Matera A Gregory, Misteli Tom
National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
J Cell Biol. 2004 Mar 15;164(6):831-42. doi: 10.1083/jcb.200311121.
Cajal bodies (CBs) are subnuclear domains implicated in small nuclear ribonucleoprotein (snRNP) biogenesis. In most cell types, CBs coincide with nuclear gems, which contain the survival of motor neurons (SMN) complex, an essential snRNP assembly factor. Here, we analyze the exchange kinetics of multiple components of CBs and gems in living cells using photobleaching microscopy. We demonstrate differences in dissociation kinetics of CB constituents and relate them to their functions. Coilin and SMN complex members exhibit relatively long CB residence times, whereas components of snRNPs, small nucleolar RNPs, and factors shared with the nucleolus have significantly shorter residence times. Comparison of the dissociation kinetics of these shared proteins from either the nucleolus or the CB suggests the existence of compartment-specific retention mechanisms. The dynamic properties of several CB components do not depend on their interaction with coilin because their dissociation kinetics are unaltered in residual nuclear bodies of coilin knockout cells. Photobleaching and fluorescence resonance energy transfer experiments demonstrate that coilin and SMN can interact within CBs, but their interaction is not the major determinant of their residence times. These results suggest that CBs and gems are kinetically independent structures.
卡哈尔体（CBs）是参与小核核糖核蛋白（snRNP）生物合成的亚核结构域。在大多数细胞类型中，CBs与核宝石结构重合，核宝石结构包含运动神经元存活蛋白（SMN）复合体，这是一种重要的snRNP组装因子。在此，我们使用光漂白显微镜分析了活细胞中CBs和核宝石结构多种成分的交换动力学。我们证明了CB成分解离动力学的差异，并将其与它们的功能联系起来。卷曲螺旋蛋白和SMN复合体成员在CB中的停留时间相对较长，而snRNPs、小核仁核糖核蛋白的成分以及与核仁共有的因子的停留时间则明显较短。这些共享蛋白从核仁或CB解离动力学的比较表明存在特定隔室的保留机制。几种CB成分的动态特性并不取决于它们与卷曲螺旋蛋白的相互作用，因为它们在卷曲螺旋蛋白敲除细胞的残留核体中的解离动力学未发生改变。光漂白和荧光共振能量转移实验表明，卷曲螺旋蛋白和SMN可以在CBs内相互作用，但它们的相互作用不是其停留时间的主要决定因素。这些结果表明，CBs和核宝石结构在动力学上是独立的结构。
