Ref ID : 7699
C. Caratero, J.C. Bes, A. Caratero, and H. Planel; [Etude Ultrastructurale du Nucleole et de la Nucleologenese chez Tetrahymena pyriformis]. Protistologica XIX(2):177-186, 1983
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An ultrastructure study of the macronucleus of Tetrahymena allowed, at least in part, the normal nucleolar structure to be defined. Our investigation showed that the dense central fibrillar region, which contains DNA, as demonstrated by Charret (1969) also contains RNP. It can not therefore be considered as a zone without transcriptional activity. Furthermore, actinomycine D which in Tetrahymena causes nucleolar fusion can, under certain experimental conditions, bring about segregation of the nucleolar components. This is the first time that such a phenomenon has been observed in Tetrahymena. Overall, these results have allowed us to propose an organizational structure for the nucleolus of Tetrahymena pyriformis. This investigation also presents the first electron micrographs of nucleologenesis occuring during conjugation accompagnying ribosomal DNA amplification. The nucleoli first appear in the centre of the nucleus in rod or crescent shapes; they are smaller than adult nucleoli. Nucleologenesis was never seen to occur near the periphery of the nucleus.