Ref ID : 7676
Marina Frenkel; Tillina magna (Ciliophora, Colpodidae): Structural Changes of the Macronucleus Correlated with its Division. Protistologica XVIII(2):259-272, 1982
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Many compact chromatin aggregates are formed in the predivisional macronucleus of Tillina magna. During the two consecutive nuclear divisions, these aggregates are segregation units similar to those of other Colpodidae. In Tillina magna, they are formed by contraction of the macronuclear chromatin strands into a number of individual stellate clusters. The chromatin strands are coiled chromosome-like structures likely to be aggregates of several chromosomes. Some of the macronuclear segregation units get enclosed into the large single extrusion body which separates from every daughter nucleus after both the first and the second divisions. These data are consistent with the polygenomic model of the macronucleus of Colpodidae. Electron microscopy shows that the condensed macronuclear chromatin of Tillina magna is represented by typical << small bodies >>. Like in Colpoda steini, only redistribution of the macronuclear material but no ultrastructural changes of the chromatin << small bodies >> occur during the predivisional reorganization. The general ultrastructural pattern of macronuclear division corresponds sufficiently well to the light microscopical observations. The fine structure of the large extrusion bodies does not differ from that of the rest of the macronucleus, at least at the moment of their separation (following each division). Shortly before the macronucleus divides, numerous small fragments separate from its surface. These fragments can be seen only with the electron microscope and contain loose fibro-granular material but neither condensed chromatin nor nucleolar fibrillar cores. Extrusion of this type seems to be correlated with the predivisional reorganization of the macronucleus. The dividing macronucleus contains bundles of microtubules.