蚕豆细胞核仁和核质中剪接因子SC35的定位研究

LOCALIZATION OF SC35 IN THE NUCLEOLUS AND NUCLEOPLASM OF THE ROOT MERISTEMATIC CELLS OF VICIA FABA

本文以蚕豆(Vicia faba L.)根端分生组织细胞为材料,以抗SC35抗体为探针,在电镜下对SC35在高等植物细胞中的存在与否和分布特点进行了研究,发现经抗SC35抗体标记后,标明SC35位置的胶体金颗粒主要分布于核仁的致密纤维组分(DFC)、核质的染色质间颗粒(IGs)和染色质周边纤维处(PFs),而核仁的纤维中心(FC)、核仁液泡和集缩染色质团块中央部位的金颗粒很少。DFC, IGs和PFs处的金颗粒平均密度分别为65.89个/μm^2和36.28个/μm^2,远远高于集缩染色质团块中央部位以及FC和核仁液泡处的金颗粒平均密度(分别为5.90个/μm^2和6.26个/μm^2)。说明蚕豆细胞核仁的DFC,核质的IGs和PFs处富含剪接因子SC35。本文研究结果表明,SC35或SC35类蛋白在蚕豆细胞核质中的分布与其在哺乳动物细胞核质中的分布规律相似。同时本文首次报道了SC35或SC35类蛋白存在于核仁中。

SC35 is a non-snRNP spliceosome component purified from mammalian cells by Fu and Maniatis in 1990. In vitro splicing assays showed that SC35 plays a key role in splicing site selection and ATP-dependent pre-spliceosome assembly. In the mammalian nucleus, SC35 has been localized to distinct and dynamic nuclear domains : immunofluorescence observations revealed the presence of SC35 in speckles distributed in various regions throughout the nucleo-plasm, which, as identified with immunoelectron microscopy, correspond to the interchromatin granules (IGs) and perichromatin fibrils (PFs). However, there has been no report regarding the presence and distribution pattern of SC35 in higher plant nuclei. Engage in such studies will surely contribute to our understanding of RNA processing and the spatial organization or structure basis of this process in higher plant. In this article, we studied the distribution pattern of SC35 in the nucleus of the root meris-tematic cells of Vicia faba by immunoelectron microscopy. After immunolabeling with anti-SC35 mAb and protein A-colloidal gold, IGs and PFs in the nucleoplasm and dense fibrillar component (DFC) of the nucleolus were heavily labeled with gold particles, while only a few of the gold particles were found in fibrillar centers (FC) and nucleolar vacuoles (NV) of the nucleolus and the central domains of the condensed chromatin. Densities of gold particles in the areas of DFC and the area of IGs plus PFs were 65. 89/μm2 and 36. 28 /μm2 respectively, much higher than that of the central domain of condensed chromatin and that of FC plus NV, which were only 5. 90/μm2 and 6. 26/μm2 respectively. This indicates that DFC of the nucleolus and the area of IGs plus PFs of the nucleoplasm are enriched with SC35 or SC35-like protein. The distribution pattern of SC35 or SC35-like protein in the nucleoplasm of Vicia faba is similar to that of the mammalian nuclei. To the authors' knowledge, it is a new finding that SC35 or SC35-like protein exists in the nucleolus.