University of Barcelona, Department of Genetics, IBUB, Av. Diagonal 645, 08028, Barcelona, Spain.
Development. 2010 Apr;137(7):1055-65. doi: 10.1242/dev.042564.
Planarians are an ideal model system to study in vivo the dynamics of adult pluripotent stem cells. However, our knowledge of the factors necessary for regulating the 'stemness' of the neoblasts, the adult stem cells of planarians, is sparse. Here, we report on the characterization of the first planarian member of the LSm protein superfamily, Smed-SmB, which is expressed in stem cells and neurons in Schmidtea mediterranea. LSm proteins are highly conserved key players of the splicing machinery. Our study shows that Smed-SmB protein, which is localized in the nucleus and the chromatoid body of stem cells, is required to safeguard the proliferative ability of the neoblasts. The chromatoid body, a cytoplasmatic ribonucleoprotein complex, is an essential regulator of the RNA metabolism required for the maintenance of metazoan germ cells. However, planarian neoblasts and neurons also rely on its functions. Remarkably, Smed-SmB dsRNA-mediated knockdown results in a rapid loss of organization of the chromatoid body, an impairment of the ability to post-transcriptionally process the transcripts of Smed-CycB, and a severe proliferative failure of the neoblasts. This chain of events leads to a quick depletion of the neoblast pool, resulting in a lethal phenotype for both regenerating and intact animals. In summary, our results suggest that Smed-SmB is an essential component of the chromatoid body, crucial to ensure a proper RNA metabolism and essential for stem cell proliferation.
涡虫是研究成体多能干细胞体内动力学的理想模式生物。然而，我们对调节涡虫成体干细胞（neoblasts）“干性”的因素知之甚少。在这里，我们报告了第一个 LSm 蛋白超家族的扁形动物成员 Smed-SmB 的特征，该蛋白在 Schmidtea mediterranea 中的干细胞和神经元中表达。LSm 蛋白是剪接机制中高度保守的关键因子。我们的研究表明，Smed-SmB 蛋白定位于干细胞的核和染色质体中，对于维持 neoblasts 的增殖能力是必需的。染色质体是一种细胞质核糖核蛋白复合物，是维持后生动物生殖细胞所必需的 RNA 代谢的重要调节剂。然而，扁形动物的 neoblasts 和神经元也依赖于它的功能。值得注意的是，Smed-SmB dsRNA 介导的敲低会导致染色质体的快速失去组织，转录后处理 Smed-CycB 转录本的能力受损，以及 neoblasts 的严重增殖失败。这一连串的事件导致 neoblast 池迅速耗尽，导致再生和完整动物的致命表型。总之，我们的结果表明，Smed-SmB 是染色质体的一个必需组成部分，对于确保适当的 RNA 代谢和维持干细胞增殖至关重要。
