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Nucleolus

About: Nucleolus is a research topic. Over the lifetime, 5873 publications have been published within this topic receiving 232435 citations. The topic is also known as: GO:0005730 & cell nucleolus.


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Journal ArticleDOI
TL;DR: The onset of RNA synthesis in developing early pig embryos from 1-cell to 8-cell and morula stages was studied using high-resolution autoradiography of (5-3H)uridine incorporation, with some nucleoli being more reticulated and showing more transcriptional activity than others.
Abstract: The onset of RNA synthesis in developing early pig embryos from 1-cell to 8-cell and morula stages was studied using high-resolution autoradiography of (5-3H)uridine incorporation. No transcriptional activity was detected in nuclei of 1- and 2- cell stage embryos with this technique. In these embryos nucleolus-like bodies (NLB) consist of sharply delineated, round, electron dense fibrillar masses. In the 4-cell stage embryos, the first uridine-3H incorporation in the nucleoplasm was detected and localized mainly near the regions of condensed chromatin. The first signs or reticulation and chromatin association were observed at the periphery of NLBs. In the next cell cycle (5- to 8-cell embryos) uridine-3H labelling was detected in the nucleoplasm and nucleoli. In these embryos, nucleoli consist of a central dense fibrillar mass without any transcriptional activity and fibrillo-granular cortex over which label was localized. The degree of functional restructure of nucleoli was variable within one blastomere or among different blastomeres, some nucleoli being more reticulated and showing more transcriptional activity than others. Fully developed nucleoli were present in early morulae. Electron dense unidentified structures described here as small dense roundshaped bodies (RDB) often surrounded by blocks of large chromatin granules were observed in intact 2-cell and alpha-amanitin treated 4-cell stage embryos. These structures did not show any transcriptional activity

86 citations

Journal ArticleDOI
TL;DR: It is demonstrated here that IRS-1 binds also to the phosphatidylinositol 3-kinase (PI3-K) subunits in nuclear extracts, and that the p110 subunit of PI3- K directly phosphorylates and activates UBF1, an exclusively nucleolar protein.
Abstract: The insulin-like growth factor I/insulin receptor substrate 1 axis controls, in a nonredundant way, ≈50% of cell and body size in animals from Drosophila to mice and in cells in culture. Although other factors may also intervene, cell size is strongly dependent on ribosome biogenesis, which is under the control of RNA polymerase I activity. We have previously shown that insulin receptor substrate 1 (IRS-1) translocates to the nuclei and nucleoli, where it binds to the upstream binding factor (UBF) 1, a regulator of RNA polymerase I activity. Activation of UBF1 requires its phosphorylation. However, IRS-1 is not a kinase, and we searched for an intermediate kinase that can phosphorylate UBF1. We demonstrate here that IRS-1 binds also to the phosphatidylinositol 3-kinase (PI3-K) subunits in nuclear extracts, and that the p110 subunit of PI3-K directly phosphorylates and activates UBF1, an exclusively nucleolar protein. The interaction of IRS-1, PI3-K, and UBF1 in the nucleoli provides one of the mechanisms for the effects of IRS-1 on cell and body size.

86 citations

Journal ArticleDOI
TL;DR: This mini-review will focus on the modes of action of nucleolar stress and discuss how the manipulation ofucleolar activity might underscore novel strategies to extend neuronal function and survival.
Abstract: Nucleoli are the sites where synthesis of rRNA and ribosomal assembly take place Along with these “traditional” roles, the nucleolus controls cellular physiology and homeostasis The cellular and molecular alterations associated with impaired nucleolar activity (“nucleolar stress”) have just started to be systematically explored in the nervous system taking advantage of newly available animal models lacking rRNA synthesis in specific neurons These studies showed that nucleolar function is necessary for neuronal survival and that its modality of action differs between and within cell types Nucleolar function is also crucial in pathology as it controls mitochondrial activity and critical stress signaling pathways mimicking hallmarks of human neurodegenerative diseases This mini-review will focus on the modes of action of nucleolar stress and discuss how the manipulation of nucleolar activity might underscore novel strategies to extend neuronal function and survival

86 citations

Journal ArticleDOI
TL;DR: The cytological localization of rRNA synthesis, transport, and processing events within the mammalian cell nucleolus is examined by double-label fluorescent in situ hybridization analysis using probes for small selected segments of pre-rRNA, which have known half-lives.
Abstract: We have examined the cytological localization of rRNA synthesis, transport, and processing events within the mammalian cell nucleolus by double-label fluorescent in situ hybridization analysis using probes for small selected segments of pre-rRNA, which have known half-lives. In particular, a probe for an extremely short-lived 5′ region that is not found separate of the pre-rRNA identifies nascent transcripts within the nucleolus of an intact active cell, while other characterized probes identify molecules at different stages in the rRNA processing pathway. Through these studies, visualized by confocal and normal light microscopy, we (1) confirm that rDNA transcription occurs in small foci within nucleoli (2) show that the nascent pre-rRNA transcripts and most likely also the rDNA templates are surprisingly extended in the nucleolus, (3) provide evidence that the 5′ end of the nascent rRNA transcript moves more rapidly away from the template DNA than does the 3′ end of the newly released transcript, and (4) demonstrate that the various subsequent rRNA processing steps occur sequentially further from the transcription site, with each early processing event taking place in a distinct nucleolar subdomain. These last three points are contrary to the generally accepted paradigms of nucleolar organization and function. Our findings also imply that the nucleolus is considerably more complex than the conventional view, inferred from electron micrographs, of only three kinds of regions—fibrillar centers, dense fibrillar components, and granular components—for the dense fibrillar component evidently consists of several functionally distinct sub-domains that correlate with different steps of ribosome biogenesis.

86 citations

Journal ArticleDOI
TL;DR: By combining cryofixation and cryosubstitution in a structural and functional analysis of the nucleus of Saccharomyces cerevisiae, morphological subcompartments in the nucleolus are identified and it is suggested that ribosomal transcripts are distributed along a nucleolar network that might include both DFC and GC.
Abstract: By combining cryofixation and cryosubstitution in a structural and functional analysis of the nucleus of Saccharomyces cerevisiae, we identified morphological subcompartments in the nucleolus. These were similar to those of nucleoli of higher eukaryotes, such as the fibrillar centre (FC), the dense fibrillar component (DFC) and the granular component (GC). In situ hybridization and immunocytochemistry revealed RNA polymerase I and proteins involved in early steps of ribosomal maturation along the DFC, while the ribosomal genes were detected at the FCs. Our results also suggest that ribosomal transcripts are distributed along a nucleolar network that might include both DFC and GC. We also show that pre-ribosomal subunits may be exported along tracks to the cytoplasm. Export takes place through all the pores of the nuclear envelope, not just those in contact with the nucleolus. Moreover, comparison of the nucleolar organization in S. cerevisiae and in Schizosaccharomyces pombe demonstrated than the distribution of the 5S genes with respect to the 35S transcription unit does not modify the organization of the nucleolus. We also report, for the first time, the ultrastructural localization of RNA polymerase II in yeast. The distribution of RNA polymerase II and morphological details that could be observed in the extra-nucleolar region of cryofixed cells provided cytological evidence of a peripheral region extending along the nuclear envelope that could correspond to heterochromatin in higher eukaryotes.

86 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023145
2022209
2021143
2020125
2019139
2018121