The Prp19 Complex Directly Functions in Mitotic Spindle Assembly

The conserved Prp19 (pre-RNA processing 19) complex is required for pre-mRNA splicing in eukaryotic nuclei. Recent RNAi screens indicated that knockdown of Prp19 complex subunits strongly delays cell proliferation. Here we show that knockdown of the smallest subunit, BCAS2/Spf27, destabilizes the entire complex and leads to specific mitotic defects in human cells. These could result from splicing failures in interphase or reflect a direct function of the complex in open mitosis. Using Xenopus extracts, in which cell cycle progression and spindle formation can be reconstituted in vitro, we tested Prp19 complex functions during a complete cell cycle and directly in open mitosis. Strikingly, immunodepletion of the complex either before or after interphase significantly reduces the number of intact spindles, and increases the percentage of spindles with lower microtubule density and impaired metaphase alignment of chromosomes. Our data identify the Prp19 complex as the first spliceosome subcomplex that directly contributes to mitosis in vertebrates independently of its function in interphase.

保守的Prp19（pre-RNA processing 19）复合物是真核细胞核内前mRNA剪接所必需的。近期的RNA干扰（RNAi）筛选实验显示，敲低Prp19复合物亚基会显著延缓细胞增殖。本研究证实，敲低其最小亚基BCAS2/Spf27会使整个复合物不稳定，并在人类细胞中引发特异性有丝分裂缺陷。这类缺陷可能源于间期的剪接失败，也可能反映了该复合物在开放式有丝分裂中的直接功能。我们利用可在体外重建细胞周期进程与纺锤体形成的爪蟾提取物，检测了Prp19复合物在完整细胞周期及开放式有丝分裂中的直接功能。值得注意的是，无论在间期前还是间期后对该复合物进行免疫耗竭，均会显著减少完整纺锤体的数量，并提升微管密度较低、染色体中期排列异常的纺锤体所占比例。本研究数据证实，Prp19复合物是首个被发现的、可独立于间期功能之外直接参与脊椎动物有丝分裂的剪接体（spliceosome）亚复合物。