Chen Y, Zhang B, Luo W J, Zhai Z H
College of Life Sciences, Peking University, Beijing.
Shi Yan Sheng Wu Xue Bao. 1996 Sep;29(3):255-67.
Nuclei assembled in Xenopus egg extracts from exogenous DNA or chromatin are morphologically similar to normal eukaryotic nuclei except that they do not contain nucleolus-like structure. Previous work show that prenucleolar bodies could be found in these nuclei, but they are unable to fuse with each other, probably due to the absence of a functional nucleolus organizer. It is interesting to know if exogenous functional nuclei could act as functional nucleolus organizer to induce the formation of mature nucleoli. To test this possibility, nucleoli and demembranated macronuclei which contain perinuclear distributed nucleoli were isolated and purified from Tetrahymena shanghaiensis and were introduced into Xenopus cell-free system. By EM observation, we showed that these nucleoli, both individual isolated and perinuclear distributed, could not keep their original morphological characteristic, but undergo a series of structural changes resembling nuclear assembly induced by exogenous chromatin. No nucleolus-like structure was found in these nuclear like structure. These results indicate that functional nucleolus organizers could neither keep their original activity of RNA transcription nor induce the formation of new nucleoli in Xenopus egg extracts.
从外源DNA或染色质在非洲爪蟾卵提取物中组装的细胞核在形态上与正常真核细胞核相似，只是它们不包含核仁样结构。先前的研究表明，在这些细胞核中可以发现前核仁体，但它们无法相互融合，这可能是由于缺乏功能性核仁组织区。了解外源功能性细胞核是否可以作为功能性核仁组织区来诱导成熟核仁的形成很有意思。为了测试这种可能性，从上海四膜虫中分离并纯化了核仁以及含有核周分布核仁的去膜大核，并将其引入非洲爪蟾无细胞体系。通过电子显微镜观察，我们发现这些核仁，无论是单个分离的还是核周分布的，都不能保持其原始形态特征，而是经历了一系列类似于外源染色质诱导的核组装的结构变化。在这些类核结构中未发现核仁样结构。这些结果表明，功能性核仁组织区在非洲爪蟾卵提取物中既不能保持其原始的RNA转录活性，也不能诱导新核仁的形成。
