Quantitative analysis of nucleolar chromatin distribution in the complex convoluted nucleoli of Didinium nasutum (Ciliophora)

Abstract

We have earlier shown that the typical Didinium nasutum nucleolus is a complex convoluted branched domain, comprising a dense fi brillar component located at the periphery of the nucleolus and a granular component located in the central part. Here our main interest was to study quantitatively the spatial distribution of nucleolar chromatin structures in these convoluted nucleoli. There are no "classical" fi brillar centers in D.nasutum nucleoli. The spatial distribution of nucleolar chromatin bodies, which play the role of nucleolar organizers in the macronucleus of D.nasutum, was studied using 3D reconstructions based on serial ultrathin sections. The relative number of nucleolar chromatin bodies was determined in macronuclei of recently fed, starved D.nasutum cells and in resting cysts. This parameter is shown to correlate with the activity of the nucleolus. However, the relative number of nucleolar chromatin bodies in diff erent regions of the same convoluted nucleolus is approximately the same. This fi nding suggests equal activity in diff erent parts of the nucleolar domain and indicates the existence of some molecular mechanism enabling it to synchronize this activity in D. nasutum nucleoli. Our data show that D. nasutum nucleoli display bipartite structure. All nucleolar chromatin bodies are shown to be located outside of nucleoli, at the periphery of the fi brillar component.

Effects of Lead on the Morphology and Structure of the Nucleolus in the Root Tip Meristematic Cells of Allium cepa L.

“…The nucleolus is a highly dynamic subnuclear domain where rRNA synthesis, rRNA processing and assembly of ribosomal subunits take place [26]. It plays important roles in the regulation of many fundamental cellular processes, including cell cycle regulation, apoptosis, telomerase production, and the monitoring and response to cellular stress [27,28].…”

Localization of fibrillarin in the nucleoli of ciliate species with subchromosomal organization of macronuclear genome

“…Using three-dimensional electron microscopy reconstructions, it has been shown that D. nasutum nucleoli, looking on the single sections like individual separate structures, are parts of the large complicated branchy nucleolar networks (Leonova et al, 2006(Leonova et al, , 2012(Leonova et al, , 2013. 3D models built on the basis of serial ultrathin sections show that in these nucleolar domains the fibrillar component is located at the periphery, while the granular part is in the central part of the nucleolus (Leonova et al, 2006).…”

“…Fibrillarin homologues are present in the cells of various species from Archaea to human (Henriquez et al, 1990;Amiri, 1994;Amin et al, 2007). Fibrillarin plays an important role in early processing and modification of pre-rRNA, ribosome assembly, and is also essential for early embryonic development (Fomproix et al, 1989;Tollervey et al, 1993;Newton et al, 2003). Moreover, fibrillarin plays a critical role in the maintenance of nuclear shape and cellular growth (Amin et al, 2007).…”

Electron Microscopic Identification of Rna- And Dna- Containing Structures in the Preparations of Isolated Macronuclei of Ciliates Bursaria Truncatella

“…It was shown that in "gene-sized" species Stylonychia lemnae rRNA is processed in a bipartite and inverse manner compared to a typical metazoan nucleolar organization (Postberg et al, 2006). The nucleoli of another ciliate, Didinium nasutum, also display the bipartite structure, with an inverted disposition of its main components (Leonova et al, 2006(Leonova et al, , 2012(Leonova et al, , 2013.…”