Siebrasse Jan Peter, Veith Roman, Dobay Akos, Leonhardt Heinrich, Daneholt Bertil, Kubitscheck Ulrich
Institute for Physical and Theoretical Chemistry, Wegelerstrasse 12, Rheinische Friedrich Wilhelms University Bonn, D-53115 Bonn, Germany.
Proc Natl Acad Sci U S A. 2008 Dec 23;105(51):20291-6. doi: 10.1073/pnas.0810692105. Epub 2008 Dec 12.
Messenger ribonucleoprotein particles (mRNPs) move randomly within nucleoplasm before they exit from the nucleus. To further understand mRNP trafficking, we have studied the intranuclear movement of a specific mRNP, the BR2 mRNP, in salivary gland cells in Chironomus tentans. Their polytene nuclei harbor giant chromosomes separated by vast regions of nucleoplasm, which allows us to study mRNP mobility without interference of chromatin. The particles were fluorescently labeled with microinjected oligonucleotides (DNA or RNA) complementary to BR2 mRNA or with the RNA-binding protein hrp36, the C. tentans homologue of hnRNP A1. Using high-speed laser microscopy, we followed the intranuclear trajectories of single mRNPs and characterized their motion within the nucleoplasm. The Balbiani ring (BR) mRNPs moved randomly, but unexpectedly, in a discontinuous manner. When mobile, they diffused with a diffusion coefficient corresponding to their size. Between mobile phases, the mRNPs were slowed down 10- to 250-fold but were never completely immobile. Earlier electron microscopy work has indicated that BR particles can attach to thin nonchromatin fibers, which are sometimes connected to discrete fibrogranular clusters. We propose that the observed discontinuous movement reflects transient interactions between freely diffusing BR particles and these submicroscopic structures.
信使核糖核蛋白颗粒（mRNPs）在从细胞核排出之前在核质中随机移动。为了进一步了解mRNP的运输，我们研究了一种特定的mRNP——BR2 mRNP在摇蚊唾液腺细胞中的核内移动。它们的多线核含有由大片核质分隔的巨大染色体，这使我们能够在不受染色质干扰的情况下研究mRNP的移动性。这些颗粒用与BR2 mRNA互补的显微注射寡核苷酸（DNA或RNA）或用RNA结合蛋白hrp36（hnRNP A1的摇蚊同源物）进行荧光标记。使用高速激光显微镜，我们追踪了单个mRNP的核内轨迹，并表征了它们在核质中的运动。巴尔比亚尼环（BR）mRNPs随机移动，但出乎意料的是，它们以不连续的方式移动。当处于移动阶段时，它们以与其大小相对应的扩散系数进行扩散。在移动阶段之间，mRNPs的移动速度减慢了10到250倍，但从未完全静止。早期的电子显微镜研究表明，BR颗粒可以附着在细的非染色质纤维上，这些纤维有时与离散的纤维颗粒簇相连。我们认为，观察到的不连续运动反映了自由扩散的BR颗粒与这些亚微观结构之间的瞬时相互作用。
