[Chromosome-like bodies of dysentery ameba Entamoeba histolytica]

Intact and surface stretched amembraneous nuclei of Entamoeba histolytica (Rhizopoda, Lobosea, Entamoebidae) trophozoites were studied by light and electron microscopy. A moderately dense karyosome about 1.5 microns in diameter, localized in the central part of the interphase nucleus, contains the bulk of nuclear DNA. Within the karyosome, beaded and ribbon-like chromatin bodies surrounding a loose fibrillar core are commonly recognized. The peripheral domain of both interphase and several mitotic nuclei is filled with a heterogeneous material similar in its ultrastructure to the nucleolar substance. A wide fibrogranular domain lies between this unusual nucleolus and the karyosome. Rosette-like intranuclear inclusions 0.2-0.4 micron in diameter are often seen in both the fibrogranular and nucleolar domains. At the prophase-metaphase, nearly 50 linear chromosome-like bodies are detected as being in close association with several large beaded and ribbon-like chromatin bodies. At the anaphase-telophase, the chromatin bodies per surface-stretched daughter nucleus of live entamoebae, and in each amembraneous daughter nuclear preparation number nearly 14 and 6, respectively. Besides, in each amembraneous DAPI-stained nucleus a set of 50 or so linear chromosome-like bodies are clearly identified. We infer that the nucleus of E. histolytica contains more than 50 linear chromosomes which at different stages of the cell cycle can unite into several beaded and ribbon-like associations. These form a single moderately dense chromatin karyosome in the central part of the interphase nucleus.