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Nucleolar Structure and Function in Trypanosomatid Protozoa

Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Av. de los Barrios 1, Col. Los Reyes Iztacala, Tlalnepantla CP 54090, Estado de México, Mexico
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Cells 2019, 8(5), 421; https://doi.org/10.3390/cells8050421
Received: 2 April 2019 / Revised: 26 April 2019 / Accepted: 28 April 2019 / Published: 8 May 2019
(This article belongs to the Special Issue Nucleolar Organization and Functions in Health and Disease)
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Abstract

The nucleolus is the conspicuous nuclear body where ribosomal RNA genes are transcribed by RNA polymerase I, pre-ribosomal RNA is processed, and ribosomal subunits are assembled. Other important functions have been attributed to the nucleolus over the years. Here we review the current knowledge about the structure and function of the nucleolus in the trypanosomatid parasites Trypanosoma brucei, Trypanosoma cruzi and Leishmania ssp., which represent one of the earliest branching lineages among the eukaryotes. These protozoan parasites present a single nucleolus that is preserved throughout the closed nuclear division, and that seems to lack fibrillar centers. Trypanosomatids possess a relatively low number of rRNA genes, which encode rRNA molecules that contain large expansion segments, including several that are trypanosomatid-specific. Notably, the large subunit rRNA (28S-type) is fragmented into two large and four small rRNA species. Hence, compared to other organisms, the rRNA primary transcript requires additional processing steps in trypanosomatids. Accordingly, this group of parasites contains the highest number ever reported of snoRNAs that participate in rRNA processing. The number of modified rRNA nucleotides in trypanosomatids is also higher than in other organisms. Regarding the structure and biogenesis of the ribosomes, recent cryo-electron microscopy analyses have revealed several trypanosomatid-specific features that are discussed here. Additional functions of the nucleolus in trypanosomatids are also reviewed. View Full-Text
Keywords: nucleolus; trypanosomatid parasites; Pol I; rRNA; ribosome biogenesis; snoRNA; snoRNP nucleolus; trypanosomatid parasites; Pol I; rRNA; ribosome biogenesis; snoRNA; snoRNP
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Martínez-Calvillo, S.; Florencio-Martínez, L.E.; Nepomuceno-Mejía, T. Nucleolar Structure and Function in Trypanosomatid Protozoa. Cells 2019, 8, 421.

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