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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7583

Igor B. Raikov and V.G. Kovaleva; Fine Structural Morphology and Cytochemistry of the Nuclei of the Lower Marine Ciliate Trachelocerca geopetiti (Karyorelictida). Protistologica XVII(1):113-130, 1981

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The distribution of DNA, RNA, and protein containing structures in the nuclei of T. geopetiti has been investigated using the EDTA method of Bernhard and treatments of epoxy sections and some non-embedded specimes with pronase, DNase, and RNase. The nuclear apparatus of T. geopetiti is a group of 4 or 8 macronuclei and 2 or 4 micronuclei. The macronuclei contain very large spongy chromocentres, multiple fibro-granular nucleoli, and sometimes single dense spheres. The condensed chromatin of the chromocentres is completely bleached with EDTA and digested by a sequential treatment with pronase and DNase. However, perichromatin RNP fibrils and perichromatin-type granules are visualized both on the surface and in the inner cavities of the chromocentres following either treatment. The chromocentres thus seem to be able of peripheral transcription. The macronuclear matrix is rich in fibrogranular, RNA containing material. Only intranucleolar chromatin is bleached with EDTA in the nucleoli, whereas pronase decreases the density of all nucleolar components. The macronuclear spheres retain full contrast after EDTA treatment but are completely digested with pronase, thus being essentially proteinaceous. The spheres closely contact both the fibrillar and the granular regions of several nucleoli. The micronuclei are filled with condensed chromatin which can be bleached with EDTA. RNP-containing lamellae exist the clefts pervading the chromatin. These lamellae resemble the kinetochores of the macronuclear mitotic chromosomes and seem to be persisting interphasic kinetochores.