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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 4699

Meiying Lin and David M. Prescott; Fine Structure of the Macronuclei and Micronuclei in Five Hypotrichs. Arch.Protistenk 131:33-43, 1986

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The ultrastructure of macronuclei, including replication bands, and of micronuclei are described for 5 hypotrich species, Urostyla cristata, Holosticha sp., Styx sp., Euplotes eurystomus, and E. crassus. Macronuclei contain three major components: dispersed chromatin, condensed chromatin, and nucleoli. The dense chromatin represents the aggregation of at least most of the millions of gene-sized DNA molecules in hypotrich macronuclei. The micronuclei in all 5 species have basically the same structure, i.e. a network of tightly packed, dense chromatin. The structure of macronuclear replication bands is similar in all 5 species. The forward zone contains tightly packed fibers ~40 nm in diameter formed by dramatic reorganization of the chromatin at the leading border of the forward zone. An intermediate between chromatin and fibers is seen in U. cristata, consisting of finely divided particulate/fibrous material. The rear zone, in which DNA replication occurs, contain fibers ~10 nm in diameter. Behind the rear zone the newly replicated DNA is aggregated into dense chromatin. Nucleoli remain intact as they pass through replication bands.