Relative position of nucleolar chromatin and nucleolar components in ciliate <Emphasis Type="Italic">Didinium nasutum</Emphasis> somatic nuclei |
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Authors: | O G Leonova B P Karadzhyan Yu F Ivlev Yu L Ivanova V I Popenko |
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Institution: | 1.Engelhardt Institute of Molecular Biology,Russian Academy of Sciences,Moscow,Russia;2.Institute of Cytology,Russian Academy of Sciences,St. Petersburg,Russia;3.Severtsov Institute of Ecology and Evolution,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | According to our computer modeling data obtained earlier, nucleoli in interphase ciliates Didinium nasutum are complex netlike structures, in which the trabeculumor lamella-shaped fibrillar component is located on the periphery,
and the granular component in the central part of the nucleolus. Chromatin bodies connected with nucleoli act as the nucleolar
organizers in D. nasutum. In the present work, the arrangement of all chromatin bodies, which could correspond to nucleolar organizers by morphological
criteria, is studied by means of a 3D-reconstruction. It is shown that all of these chromatin bodies are localized outside
the nucleoli, on the fibrillar component’s periphery. Even those chromatin bodies which appeared to be completely surrounded
by the fibrillar nucleolar component on single ultrathin sections are actually settled down in nucleolus cavities open to
the nucleoplasm. This proves that the RNA processing in D. nasutum nucleoli is directed toward the center of nucleoli, where the granular component is located. The analysis of the nucleolar
chromatin distribution made it possible to conclude that different parts of the complex interfase netlike nucleoli of D. nasutum have approximately the same activity. |
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