scholarly journals Nucleolar activation and vacuolation in embryo radicle cells during early germination

1985 ◽  
Vol 76 (1) ◽  
pp. 67-83
Author(s):  
R. Deltour ◽  
T. de Barsy
Keyword(s):  
Primary Root ◽  
High Rate ◽  
Rrna Processing ◽  
Root Cells ◽  
Ribosomal Subunits ◽  
Granular Component ◽  
High Loss ◽  
Early Germination ◽  
Nucleolar Volume ◽  
Fibrillar Component

The activation of the nucleolus of primary root cells of Sinapis alba embryos during the first 72 h of germination was monitored by autoradiographic, ultrastructural and microstereological methods. Autoradiographs showed that within 48 h, the nucleolus progressively resumed the capacity to synthesize pre-rRNA molecules at a high rate. In quiescent embryos the nucleolus was small, compact and composed of mixed granular and fibrillar components. Within the first 6 h of germination a strong nucleolar vacuolation occurred, accompanied by a decrease in the volume of the nucleolus and a concomitant high loss of its ribonucleoproteins (RNPs). From 6 to 24 h, nucleolar vacuolation decreased to reach a stable level. During this last period the volume of the nucleolus increased by the accumulation of the fibrillar component resulting from a slow pre-rRNA processing. At 24 h the nucleolus presented a predominantly fibrillar texture. After 24 h, nucleolus growth continued but was due to the accumulation of the granular component, indicating that pre-rRNA processing occurred at a higher rate than during the first day of germination. From 48 h the nucleolus was composed of well-delineated granular and fibrillar areas. Dense nucleolus-associated chromatin as well as fibrillar centres were always observed during the whole period of observation. In addition, previous studies on the nucleolus of radicle cells of Zea mays embryo during early germination were completed by studying changes in the nucleolar volume and in the density of pre-ribosomal subunits of the granular component. On the basis of the data obtained with both species we suggest that a possible function for the nucleolar vacuoles is the increase in the nucleolus-nucleoplasm exchange interface in response to a rapid increase in the output of nucleolar RNPs. The nucleolar growth pattern during early germination is also discussed.

Distinguishing the sites of pre-rRNA synthesis and accumulation in Ehrlich tumor cell nucleoli

1991 ◽  
Vol 99 (4) ◽  
pp. 759-767
Author(s):  
M. Thiry ◽  
G. Goessens
Keyword(s):  
Tumor Cell ◽  
Condensed Chromatin ◽  
Rrna Genes ◽  
Rrna Synthesis ◽  
Rrna Gene ◽  
Dense Fibrillar Component ◽  
Ehrlich Tumor ◽  
Granular Component ◽  
Fibrillar Component

The precise location of transcribing rRNA genes within Ehrlich tumor cell nucleoli has been investigated using two approaches: high-resolution autoradiography of cells pulse-labelled with tritiated uridine, varying the exposure time, and in situ-in vitro transcription coupled with an immunogold labelling procedure. When autoradiographic preparations are exposed for a short time, silver grains are found associated almost exclusively with interphasic cell nucleoli. Labelling of extranucleolar areas requires longer exposure. Within the nucleolus, the first sites to be revealed are in the dense fibrillar component. Prolonging exposure increases labelling over the dense fibrillar component, with label becoming more and more apparent over the fibrillar centers. Under these conditions, however, labelling does not extend into the granular component, and no background is observed. Initiation of transcription on ultrathin cell sections occurs preferentially at the borders of condensed chromatin blocks and in their close vicinity. The condensed chromatin areas themselves remain unlabelled. Inside most nucleoli, gold-particle clusters are mainly detected in the fibrillar centers, especially at their periphery, whereas the dense fibrillar component and the granular component remain devoid of label. These results, together with previous observations made on the same cell type, clearly indicate that the fibrillar centers are the sites of rRNA gene transcription in Ehrlich tumor cell nucleoli, while the dense fibrillar component is the site of pre-rRNA accumulation.

scholarly journals Simultaneous immunoelectron microscopic visualization of protein B23 and C23 distribution in the HeLa cell nucleolus.

1989 ◽  
Vol 37 (9) ◽  
pp. 1371-1374 ◽  
Author(s):  
M Biggiogera ◽  
S Fakan ◽  
S H Kaufmann ◽  
A Black ◽  
J H Shaper ◽  
...  
Keyword(s):  
Hela Cell ◽  
Immunoelectron Microscopy ◽  
Silver Staining ◽  
Dense Fibrillar Component ◽  
Specific Antibodies ◽  
Granular Component ◽  
Protein B23 ◽  
Reported Data ◽  
Fibrillar Component

The intranucleolar distribution of phosphoproteins B23 and C23 was visualized simultaneously by post-embedding immunoelectron microscopy in HeLa cell nucleoli, using specific antibodies. The data show that proteins B23 and C23 co-localize to the same nucleolar compartments, i.e., the dense fibrillar component and the granular component. Neither of the two antibodies is significantly associated with the fibrillar centers in these cells, although the fibrillar centers appear positive after silver staining. These findings suggest that other unidentified components must be responsible for the silver staining observed in the fibrillar centers of interphase nucleoli. The results are discussed in the light of previously reported data obtained by preembedding immunolabeling techniques and by silver staining, which both suggested a localization of protein C23 inside the fibrillar centers.

scholarly journals Both endonucleolytic and exonucleolytic cleavage mediate ITS1 removal during human ribosomal RNA processing

2013 ◽  
Vol 200 (5) ◽  
pp. 577-588 ◽  
Author(s):  
Katherine E. Sloan ◽  
Sandy Mattijssen ◽  
Simon Lebaron ◽  
David Tollervey ◽  
Ger J.M. Pruijn ◽  
...  
Keyword(s):  
Ribosomal Rna ◽  
Rna Processing ◽  
Large Subunit ◽  
Genetic Diseases ◽  
Evolutionary Conservation ◽  
Rrna Processing ◽  
Ribosomal Subunits ◽  
Important Pathway ◽  
Ribosomal Rna Processing ◽  
Insight Into

Human ribosome production is up-regulated during tumorogenesis and is defective in many genetic diseases (ribosomopathies). We have undertaken a detailed analysis of human precursor ribosomal RNA (pre-rRNA) processing because surprisingly little is known about this important pathway. Processing in internal transcribed spacer 1 (ITS1) is a key step that separates the rRNA components of the large and small ribosomal subunits. We report that this was initiated by endonuclease cleavage, which required large subunit biogenesis factors. This was followed by 3′ to 5′ exonucleolytic processing by RRP6 and the exosome, an enzyme complex not previously linked to ITS1 removal. In contrast, RNA interference–mediated knockdown of the endoribonuclease MRP did not result in a clear defect in ITS1 processing. Despite the apparently high evolutionary conservation of the pre-rRNA processing pathway and ribosome synthesis factors, each of these features of human ITS1 processing is distinct from those in budding yeast. These results also provide significant insight into the links between ribosomopathies and ribosome production in human cells.

scholarly journals Intranucleolar sites of ribosome biogenesis defined by the localization of early binding ribosomal proteins

2007 ◽  
Vol 177 (4) ◽  
pp. 573-578 ◽  
Author(s):  
Tim Krüger ◽  
Hanswalter Zentgraf ◽  
Ulrich Scheer
Keyword(s):  
Ribosomal Rna ◽  
Ribosomal Proteins ◽  
Live Cell Imaging ◽  
Ribosome Biogenesis ◽  
Cell Imaging ◽  
Rrna Processing ◽  
Dense Fibrillar Component ◽  
Assembly Pathway ◽  
Fibrillar Component ◽  
Processing Steps

Considerable efforts are being undertaken to elucidate the processes of ribosome biogenesis. Although various preribosomal RNP complexes have been isolated and molecularly characterized, the order of ribosomal protein (r-protein) addition to the emerging ribosome subunits is largely unknown. Furthermore, the correlation between the ribosome assembly pathway and the structural organization of the dedicated ribosome factory, the nucleolus, is not well established. We have analyzed the nucleolar localization of several early binding r-proteins in human cells, applying various methods, including live-cell imaging and electron microscopy. We have located all examined r-proteins (S4, S6, S7, S9, S14, and L4) in the granular component (GC), which is the nucleolar region where later pre-ribosomal RNA (rRNA) processing steps take place. These results imply that early binding r-proteins do not assemble with nascent pre-rRNA transcripts in the dense fibrillar component (DFC), as is generally believed, and provide a link between r-protein assembly and the emergence of distinct granules at the DFC–GC interface.

scholarly journals Late Cytoplasmic Maturation of the Small Ribosomal Subunit Requires RIO Proteins in Saccharomyces cerevisiae

2003 ◽  
Vol 23 (6) ◽  
pp. 2083-2095 ◽  
Author(s):  
Emmanuel Vanrobays ◽  
Jean-Paul Gelugne ◽  
Pierre-Emmanuel Gleizes ◽  
Michele Caizergues-Ferrer
Keyword(s):  
18S Rrna ◽  
Nuclear Protein ◽  
Essential Gene ◽  
Sequence Similarity ◽  
Ribosomal Subunit ◽  
Rrna Processing ◽  
Ribosomal Subunits ◽  
Rrna Maturation ◽  
Cytoplasmic Maturation

ABSTRACT Numerous nonribosomal trans-acting factors involved in pre-rRNA processing have been characterized, but few of them are specifically required for the last cytoplasmic steps of 18S rRNA maturation. We have recently demonstrated that Rrp10p/Rio1p is such a factor. By BLAST analysis, we identified the product of a previously uncharacterized essential gene, YNL207W/RIO2, called Rio2p, that shares 43% sequence similarity with Rrp10p/Rio1p. Rio2p homologues were identified throughout the Archaea and metazoan species. We show that Rio2p is a cytoplasmic-nuclear protein and that its depletion blocks 18S rRNA production, leading to 20S pre-rRNA accumulation. In situ hybridization reveals that in Rio2p-depleted cells, 20S pre-rRNA localizes in the cytoplasm, demonstrating that its accumulation is not due to an export defect. We also show that both Rio1p and Rio2p accumulate in the nucleus of crm1-1 cells at the nonpermissive temperature. Nuclear as well as cytoplasmic Rio2p and Rio1p cosediment with pre-40S particles. These results strongly suggest that Rio2p and Rrp10p/Rio1p are shuttling proteins which associate with pre-40S particles in the nucleus and they are not necessary for export of the pre-40S complexes but are absolutely required for the cytoplasmic maturation of 20S pre-rRNA at site D, leading to mature 40S ribosomal subunits.

scholarly journals Naf1p, an Essential Nucleoplasmic Factor Specifically Required for Accumulation of Box H/ACA Small Nucleolar RNPs

2002 ◽  
Vol 22 (20) ◽  
pp. 7053-7065 ◽  
Author(s):  
Christophe Dez ◽  
Jacqueline Noaillac-Depeyre ◽  
Michèle Caizergues-Ferrer ◽  
Yves Henry
Keyword(s):  
Sucrose Gradient ◽  
Core Protein ◽  
Rrna Processing ◽  
Dense Fibrillar Component ◽  
Dramatic Decrease ◽  
Reading Frame ◽  
Snornp Biogenesis ◽  
Protein Components ◽  
Fibrillar Component ◽  
Two Hybrid

ABSTRACT Box H/ACA small nucleolar ribonucleoprotein particles (H/ACA snoRNPs) play key roles in the synthesis of eukaryotic ribosomes. The ways in which these particles are assembled and correctly localized in the dense fibrillar component of the nucleolus remain largely unknown. Recently, the essential Saccharomyces cerevisiae Naf1p protein (encoded by the YNL124W open reading frame) was found to interact in a two-hybrid assay with two core protein components of mature H/ACA snoRNPs, Cbf5p and Nhp2p (T. Ito, T. Chiba, R. Ozawa, M. Yoshida, M. Hattori, and Y. Sakaki, Proc. Natl. Acad. Sci. USA 98:4569-4574, 2001). Here we show that several H/ACA snoRNP components are weakly but specifically immunoprecipitated with epitope-tagged Naf1p, suggesting that the latter protein is involved in H/ACA snoRNP biogenesis, trafficking, and/or function. Consistent with this, we find that depletion of Naf1p leads to a defect in 18S rRNA accumulation. Naf1p is unlikely to directly assist H/ACA snoRNPs during pre-rRNA processing in the dense fibrillar component of the nucleolus for two reasons. Firstly, Naf1p accumulates predominantly in the nucleoplasm. Secondly, Naf1p sediments in a sucrose gradient chiefly as a free protein or associated in a complex of the size of free snoRNPs, whereas extremely little Naf1p is found in fractions containing preribosomes. These results are more consistent with a role for Naf1p in H/ACA snoRNP biogenesis and/or intranuclear trafficking. Indeed, depletion of Naf1p leads to a specific and dramatic decrease in the steady-state accumulation of all box H/ACA snoRNAs tested and of Cbf5p, Gar1p, and Nop10p. Naf1p is unlikely to be directly required for the synthesis of H/ACA snoRNP components. Naf1p could participate in H/ACA snoRNP assembly and/or transport.

Cellular Characteristics of Dinitroaniline Herbicide-Resistant Goosegrass (Eleusine indica)

Weed Science ◽  
1991 ◽  
Vol 39 (1) ◽  
pp. 6-12 ◽  
Author(s):  
Bernal E. Valverde ◽  
Arnold P. Appleby ◽  
Steven R. Radosevich ◽  
Alfred Soeldner
Keyword(s):  
North Carolina ◽  
Cell Wall ◽  
South Carolina ◽  
Cell Walls ◽  
Primary Root ◽  
Wall Material ◽  
Root Cells ◽  
Eleusine Indica ◽  
Herbicide Resistant ◽  
Transmission Electron

Primary root cells from five dinitroaniline-resistant (R) and three susceptible (S) goosegrass biotypes from North Carolina and South Carolina were observed by transmission electron microscopy to determine whether resistance was associated with changes in cell wall formation. Cell wall malformations were found in some cells from two of the R-biotypes and in one of the S-biotypes. Malformations consisted of partially deposited cell walls and the inclusion of cell wall material in the cytoplasm. Some of the affected cells also had abnormal, lobed nuclei and malformed mitochondria. There seems to be little or no correlation between dinitroaniline resistance and cell wall malformations.

Fine Structure of the Nucleolus in Normal and Mutant Xenopus Embryos

1967 ◽  
Vol 2 (2) ◽  
pp. 151-162
Author(s):  
ELIZABETH D. HAY ◽  
J. B. GURDON
Keyword(s):  
Fine Structure ◽  
Electron Microscope ◽  
Xenopus Laevis ◽  
Fibrous Material ◽  
Osmium Tetroxide ◽  
Wild Type ◽  
Granular Component ◽  
Basic Dyes ◽  
Fibrillar Component ◽  
Xenopus Laevis Embryos

Mutant and normal Xenopus laevis embryos (0-nu, 1-nu, 2-nu) were examined in the electron microscope after glutaraldehyde and/or osmium-tetroxide fixation. During cleavage both 0-nu and wild-type embryos contain multiple small nucleolar bodies, less than 1 µ in diameter, composed mainly of a fibrous material. By the end of cleavage or beginning of gastrulation, granular caps develop on the fibrous nucleolar bodies. In 1-and 2-nu cells, the multiple nucleolar bodies are replaced during gastrula and neurula stages by definitive nucleoli (2-5 µ in diameter) which contain abundant small (150 Å) granules intermingled with fibrous material. In 0-nu cells, one or two pseudonucleoli (1-3 µ in diameter) appear at about the same time that definitive nucleoli develop in wild-type cells. The multiple small nucleolar bodies disappear as the pseudonucleoli enlarge. Pseudonucleoli differ from definitive nucleoli in having a much smaller amount of the granular component, which is located as a cap on the periphery of the fibrous component and not mingled with it. The granular component of the 0-nu pseudonucleoli, however, is not distinguishable in its fine structure from the same component of normal nucleoli. In many 0-nu tadpoles at stage 41, the granular component of the nucleolus is entirely absent and the fibrillar component is very prominent. Both granular and fibrous components of the 0-nu pseudonucleoli contain RNA as judged by RNase sensitivity and staining affinity for basic dyes.

Three-dimensional electron microscopy of the internal nucleolus-associated chromatin and of the nucleolar vacuoles during early germination of Sinapis alba

1986 ◽  
Vol 82 (1) ◽  
pp. 53-71
Author(s):  
R. Deltour ◽  
H. Mosen ◽  
R. Bronchart
Keyword(s):  
Cross Section ◽  
Three Dimensional ◽  
Sinapis Alba ◽  
Serial Sections ◽  
Dense Fibrillar Component ◽  
Dimensional Electron ◽  
Early Germination ◽  
Fibrillar Component ◽  
Dense Chromatin ◽  
Nucleolar Vacuole

Spatial relationships between the internal nucleolus-associated chromatin (NAC) and the numerous nucleolar vacuoles that appear during early germination have been studied in nucleoli of quiescent (non-germinated) and early germinating embryos of Sinapis using serial sections. In quiescent non-vacuolated nucleoli, the transcriptionally inactive internal NAC is a short strand about 900 nm thick that in cross-section appears as heterogeneous fibrillar centres (FCs). At 4 and 6 h after germination one or several large networks of interconnected nucleolar vacuoles develop around the dispersing internal NAC. Clumps of dense chromatin are still present within the nucleolar vacuoles and are probably unfolding into deoxyribonucleoprotein (DNP) fibres (about 110 nm thick), which rapidly intrude within the nucleolar body and form thin chromatin threads. At 24 h after germination the internal NAC is more dispersed and forms, for its greatest part, a long thread (about 240 nm in diameter) wrapped up with a few dense fibrillar component, the whole forming the first outline of a nucleolonema. In cross-section most of the internal NAC appears as homogeneous FCs but short portions remain more condensed and appear as heterogeneous FCs always associated with a nucleolar vacuole. From 48 h the internal NAC is a longer thinner strand (about 160 nm in diameter), probably continuous and surrounded entirely by a homogeneous muff of dense fibrillar component, the whole forming a typical nucleolonema (about 950 nm thick) meandering throughout the nucleolus. Small amounts of the internal NAC still remain undispersed in the form of heterogeneous FCs associated with a nucleolar vacuole. The repeated association of nucleolar vacuoles and dispersing internal NAC suggests that they could play a role in chromatin dispersion and, or, activation by creating a favourable microenvironment.

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