Gemin proteins are required for efficient assembly of Sm-class ribonucleoproteins
Gemin proteins are required for efficient assembly of Sm-class ribonucleoproteins
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DOI：
10.1073/pnas.0508947102
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发表时间：
2005-11-29
影响因子：
11.1
通讯作者：
Matera, AG
中科院分区：
文献类型：
--
作者：
Shpargel, KB;Matera, AG
脊髓性肌萎缩症（SMA）是一种以脊髓运动神经元丧失为特征的神经退行性疾病。编码运动神经元存活（SMN）蛋白的基因在约95%的SMA病例中发生突变。SMN是包括Gemins2-7在内的大型寡聚复合物的中心成分，它是Sm蛋白在体内组装到介导前mrna剪接的小核rna （sn）上所必需和充分的。在Sm核的细胞质组装后，SMN和剪接snRNA都被导入细胞核，在Cajal小体中积累，进行额外的snRNA成熟步骤，然后靶向剪接因子区室，称为“斑点”。在这项研究中，我们通过RNA干扰（RNAi）分析了单个SMN复合体成员的功能。rnai介导的SMN、Gemin2、Gemin3和Gemin4的敲低会破坏Sm核心的组装，而Gemin5和Snurportin1的敲低则没有影响。通过表达GFP-SMN结构来恢复组装活性，该结构对RNAi具有折光性，但不包含SMA患者衍生突变的类似结构。我们的研究结果还表明，Cajal体内稳态需要SMN和持续的snRNP生物发生。SMN功能的扰动导致Cajal小体的解体和标记蛋白coilin重新定位到核仁。此外，在smn缺陷细胞中，新合成的SmB蛋白不能与U2 snRNA结合或在Cajal小体中积累。总的来说，我们的研究结果确定了Gemin3和Gemin4在Sm核心组装中的先前未被描述的功能，并将该途径的活性与SMA联系起来。
Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by loss of spinal motor neurons. The gene encoding the survival of motor neurons (SMN) protein is mutated in > 95% of SMA cases. SMN is the central component of a large oligomeric complex, including Gemins2-7, that is necessary and sufficient for the in vivo assembly of Sm proteins onto the small nuclear (sn)RNAs that mediate pre-mRNA splicing. After cytoplasmic assembly of the Sm core, both SMN and splicing snRNPs are imported into the nucleus, accumulating in Cajal bodies for additional snRNA maturation steps before targeting to splicing factor compartments known as "speckles." In this study, we analyzed the function of individual SMN complex members by RNA interference (RNAi). RNAi-mediated knockdown of SMN, Gemin2, Gemin3, and Gemin4 each disrupted Sm core assembly, whereas knockdown of Gemin5 and Snurportin1 had no effect. Assembly activity was rescued by expression of a GFP-SMN construct that is refractive to RNAi but not by similar constructs that contain SMA patient-derived mutations. Our results also demonstrate that Cajal body homeostasis requires SMN and ongoing snRNP biogenesis. Perturbation of SMN function results in disassembly of Cajal bodies and relocalization of the marker protein, coilin, to nucleoli. Moreover, in SMN-deficient cells, newly synthesized SmB proteins fail to associate with U2 snRNA or accumulate in Cajal bodies. Collectively, our results identify a previously uncharacterized function for Gemin3 and Gemin4 in Sm core assembly and correlate the activity of this pathway with SMA.