Also, the protein scaffold could be isolated independently of the DNA by treating HeLa chromosomes with micrococcal nuclease before removing the histones 23. Meanwhile, Laemmli and his colleagues showed that, after the histones and most of the nonhistone proteins were gently removed from HeLa metaphase chromosome, there existed a nonhistone protein scaffold that retained the size and shape of intact chromosome, and to which the DNA was attached, predominantly forming 1oops 20, 21, 22. The association of nuclear matrix with DNA replication, RNA transcription and processing, virus reproduction and other life activities soon becomes an exploding area of cell biology research 19. Its isolation and characterization stimulated the investigation of nuclear structure and function in eukaryotic cells. The existence of a nuclear matrix or nucleoskeleton in higher eukaryote has been demonstrated in numerous studies 12, 13, 14, 15, 16, 17, 18. It is generally agreed that the dinoflagellates are true eukaryotes, but may belong to one of the older lineage of eukaryotes and their nuclei may represent the transition stages from prokaryotic nucleoid to typical eukaryotic nucleus.Ĭompared with the detailed knowledge of the DNA on molecular level, little is yet known of its organization in the nucleus. The dinoflagellates cytoplasm contains all those organelles characteristic of eukaryotic cells. They possess a well defined nucleus, nucleolus and chromosomes, and a total DNA content and sequence complexity similar to advanced eukaryotes. On the other hand, the dinoflagellates have similarities to classic eukaryotes. In view of these unusual features, Dodge 11 introduced the term mesokaryote to distinguish dinoflagellates from eukaryotes. Dinoflagellate is one of the primitive eukaryotes and its nucleus possesses numerous unusual nuclear characteristics, such as little to no histone associated with the DNA 1, 2, lack of nucleosomes 3, 4, the presence of large amounts of the base 5−hydroxymethyluracil 5, 6, and unusual mitosis 7, 8, 9, 10. For the investigation of the development and evolution of nuclear matrix and chromosome scaffold in eukaryote, lower eukaryotes are ideal experimental models. Most of researches on nuclear matrix and chromosome scaffold were concentrated on higher eukaryotes, especially on mammalian cells. Our results demonstrated that a framework similar to the nuclear matrix and chromosome scaffold in mammalian cells appears in this primitive eukaryote,suggesting that these structures may have been originated from the early stages of eukaryote evolution. Two dimensional electrophoreses indicated that the nuclear matrix and chromosome scaffold are mainly composed of acidic proteins. This scaffold preserves the characteristic morphology of the chromosome. Moreover, we demonstrated that the dinoflagellate chromosome retains a protein scaffold after the depletion of DNA and soluble proteins. Chromosome residues are connected with nuclear matrix filaments to form a complete network spreading over the nucleus. Using selective extraction together with embeddment−free section and whole mount electron microscopy, a delicate nuclear matrix filament network was shown, for the first time, in dinoflagellate Crypthecodinium cohnii nucleus. Images of each chromosome are digitally arranged into homologous pairs (right).Dinoflagellate is one of the primitive eukaryotes, whose nucleus may represent one of the transition stages from prokaryotic nucleoid to typical eukaryotic nucleus. Chromosomes are released from nuclei and randomly dispersed (left). \): Karyotypes from a metaphase chromosome preparation from a spiny frog Quasipaa boulengeri (CC-BY Qing et al., 2012 PLoS Biology ).
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