MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK.
Exp Cell Res. 2010 Aug 15;316(14):2354-64. doi: 10.1016/j.yexcr.2010.05.001. Epub 2010 May 7.
Uridine-rich small nuclear ribonucleoproteins (U snRNPs) play key roles in pre-mRNA processing in the nucleus. The assembly of most U snRNPs takes place in the cytoplasm and is facilitated by the survival motor neuron (SMN) complex. Discrete cytoplasmic RNA granules called U bodies have been proposed to be specific sites for snRNP assembly because they contain U snRNPs and SMN. U bodies invariably associate with P bodies, which are involved in mRNA decay and translational control. However, it remains unknown whether other SMN complex proteins also localise to U bodies. In Drosophila there are four SMN complex proteins, namely SMN, Gemin2/CG10419, Gemin3 and Gemin5/Rigor mortis. Drosophila Gemin3 was originally identified as the Drosophila orthologue of human and yeast Dhh1, a component of P bodies. Through an in silico analysis of the DEAD-box RNA helicases we confirmed that Gemin3 is the bona fide Drosophila orthologue of vertebrate Gemin3 whereas the Drosophila orthologue of Dhh1 is Me31B. We then made use of the Drosophila egg chamber as a model system to study the subcellular distribution of the Gemin proteins as well as Me31B. Our cytological investigations show that Gemin2, Gemin3 and Gemin5 colocalise with SMN in U bodies. Although they are excluded from P bodies, as components of U bodies, Gemin2, Gemin3 and Gemin5 are consistently found associated with P bodies, wherein Me31B resides. In addition to a role in snRNP biogenesis, SMN complexes residing in U bodies may also be involved in mRNP assembly and/or transport.
富含尿嘧啶的小核核糖核蛋白（U snRNPs）在细胞核中前体 mRNA 的加工中发挥关键作用。大多数 U snRNPs 的组装发生在细胞质中，由运动神经元存活（SMN）复合物促进。离散的细胞质 RNA 颗粒称为 U 体，被认为是 snRNP 组装的特定部位，因为它们包含 U snRNPs 和 SMN。U 体始终与 P 体相关联，P 体参与 mRNA 降解和翻译控制。然而，其他 SMN 复合物蛋白是否也定位于 U 体仍然未知。在果蝇中，有四种 SMN 复合物蛋白，即 SMN、Gemin2/CG10419、Gemin3 和 Gemin5/Rigor mortis。果蝇 Gemin3 最初被鉴定为人类和酵母 Dhh1 的果蝇同源物，Dhh1 是 P 体的一个组成部分。通过对 DEAD 框 RNA 解旋酶的计算机分析，我们证实 Gemin3 是真核生物 Gemin3 的真正果蝇同源物，而 Dhh1 的果蝇同源物是 Me31B。然后，我们利用果蝇卵室作为模型系统，研究 Gemin 蛋白以及 Me31B 的亚细胞分布。我们的细胞学研究表明，Gemin2、Gemin3 和 Gemin5 与 SMN 共定位于 U 体中。尽管它们作为 U 体的组成部分被排除在 P 体之外，但 Gemin2、Gemin3 和 Gemin5 始终与 P 体相关联，而 Me31B 则位于 P 体中。除了在 snRNP 生物发生中的作用外，位于 U 体中的 SMN 复合物也可能参与 mRNP 的组装和/或运输。
