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Three-dimensional structure of the ciliate Didinium nasutum nucleoli
Authors:V. I. Popenko  B. P. Karajan  O. G. Leonova  S. O. Skarlato  Yu. F. Ivlev  Yu. L. Ivanova
Affiliation:(1) Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 199991, Russia;(2) Institute of Cytology, Russian Academy of Sciences, St. Petersburg, 194064, Russia;(3) Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, 119071, Russia
Abstract:The nucleolar organization in ciliate Didinium nasutum somatic interphase nuclei was studied using serial ultrathin sections and compared for various physiological states of the cell, namely, fed ciliates, starved ciliates, and dormant cysts. It has been shown that the interphase nucleoli are large structures with a complex architecture: the fibrillar component forms an intricate network in the macronucleus space, while the granular component is located inside this network. The structures looking as individual nucleoli in single sections are actually parts of branched nucleolar networks. The intricate nucleolar networks do not disintegrate after a 30-h starvation; however, the granular component becomes denser and develops numerous cavities filled with fine fibrils of a nonribonucleoprotein nature. In fed D. nasutum, the fibrillar structures on the periphery of nucleoli contain numerous pores (virtually absent in starved cell nucleoli), which can potentially serve for transporting newly synthesized rRNP. Branched nucleolar networks are undetectable in cysts. Their nucleoli are individual structures consisting mainly of the fibrogranular component.
Keywords:3D reconstruction  nucleolar structure  ciliates  macronucleus  serial ultrathin sections  electron microscopy
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