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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7698

Stefan Radzikowski; Mechanisms Controlling the Variable DNA Level in the Heteromeric Type Macronucleus of Chilodonella steini (Cyrtophoridae). Protistologica XIX(2):149-156, 1983

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The ciliate Chilodonella steini has a nuclear apparatus composed of one macronucleus of the centric heteromeric type, and one micronucleus. The variation observed in DNA level of macronuclei are the result of : a) uneven division of chromatin material during division of the macronucleus. b) the physiological state of the cell. In constant optimal culture conditions DNA content of macronuclei remains on an unvarying level, but when oxygen and food conditions deteriorate DNA content decreases. When conditions improve, however, there is an increase in DNA content in the macronucleus. In both cases, i.e. decrease and increase, there is about 8% DNA content variation per one cell cycle. Both increase and decrease in the DNA content of macronuclei are activated by the mechanism of differentiated DNA replication. In the case of deteriorating culture conditions initial DNA content (G1) is not completely doubled. When conditions improve this content is more than doubled. DNA elimination from the macronucleus was not observed during the interphase period. The sporadic elimination of chromatin observed during division cannot be considered as a mechanism controlling macronuclear DNA level, but more as a qualitative elimination mechanism. No fluctuations in DNA level caused by uneven division or culture conditions are observed in the micronucleus.