Martin M, Diaz de la Espina S M, Javier Medina F
Centro de Investigaciones Biológicas (C.S.I.C.), Madrid, Spain.
Chromosoma. 1989 Nov;98(5):368-77. doi: 10.1007/BF00292390.
Intranucleolar DNA, including ribosomal DNA (rDNA), was localized in situ in proliferating onion cells under the electron microscope using an anti-DNA monoclonal antibody and a postembedding indirect immunogold procedure. In the interphase nucleolus of this species, characterized by a very high amount of rRNA genes, we found DNA concentrated mostly in fibrillar centres (FCs) and in the region of the dense fibrillar component (DFC) immediately surrounding them. Clusters of gold particles were frequently seen covering both of these structural components of the nucleolus at the same time. Moreover, the same technique, applied to transcriptionally arrested quiescent onion cells, showed the nucleolar DFC devoid of DNA. Also, in mitotic cells at telophase, the prenucleolar material, which has the same morphological and cytochemical features as the DFC, does not contain DNA. These data suggest the existence of at least two subcomponents of the DFC in the onion cell nucleolus, one associated with pre-rRNA synthesis, and the other, with further processing of transcripts, already released from the rDNA template. We conclude that the first subcomponent forms part of the "transition between FC and DFC", which is the in situ structural counterpart of pre-rRNA synthesis. This transition is morphologicaly sizeable in onion cells, because of their high number of rRNA genes and the large size of the DFC mass; however, it would be largely detectable in situ in other cell systems, where the whole DFC comprises only a thin layer and the amount of rDNA is considerably reduced.
利用抗DNA单克隆抗体和包埋后间接免疫金标法，在电子显微镜下对增殖的洋葱细胞中的核仁内DNA（包括核糖体DNA，rDNA）进行了原位定位。在该物种的间期核仁中，其特征是含有大量的rRNA基因，我们发现DNA主要集中在纤维中心（FCs）以及紧邻它们的致密纤维组分（DFC）区域。经常可以看到金颗粒簇同时覆盖着核仁的这两个结构组分。此外，将同样的技术应用于转录停滞的静止洋葱细胞时，发现核仁DFC不含DNA。同样，在有丝分裂末期的细胞中，具有与DFC相同形态和细胞化学特征的前核仁物质也不含DNA。这些数据表明，洋葱细胞核仁的DFC中至少存在两个亚组分，一个与前体rRNA合成相关，另一个与已从rDNA模板释放的转录本的进一步加工相关。我们得出结论，第一个亚组分构成了“FC与DFC之间的过渡区域”的一部分，这是前体rRNA合成的原位结构对应物。由于洋葱细胞中rRNA基因数量众多且DFC体积较大，这种过渡在形态上较为显著；然而，在其他细胞系统中，整个DFC仅由一层薄层组成且rDNA数量大幅减少的情况下，这种过渡在原位也能在很大程度上被检测到。
