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At least 73 records · Page 4Linked to original sources
PubMed1991

On the regulation of DNA methylation by higher-order structure in the cell nucleus.

Several years ago it was postulated that DNA methylation may play a role in the regulation of gene activity in animal cells. Progress has been made in establishing the mechanisms by which methylation influences gene expression, but little is known about the mechanisms that control methylation itself. Here is proposed a model, susceptible of experimental confirmation, which suggests that chromatin higher-order structure is a determinant factor for the regulation of DNA methylation. The background for such a model as well as current evidence in support of it are discussed.

Animals↗
PubMedDate not supplied

[Effect of the structure of the cell nucleus chromatin on absorption of low-energy beta-radiation emitted from an incorporated source].

To study the energy absorption in cell nuclei the analysis was made of the level of registration of beta-particles, emitted by the incorporated tritium, using a liquid scintillation counter. It was shown that the treatment, modifying the chromatin structure, changed the number of beta-particles registered. The pattern of the spectral changes indicated that the effect observed was not the result of the quenching processes. The effect was absent when the source of a higher energy (14C) was used. The authors submit the conceptions concerning the mechanisms of the phenomenon observed which are confirmed by the theoretical studies.

Animals↗
PubMed2003

Morphometry and morphology of nucleus of the Sertoli and interstitial cells of the tambaqui Colossoma macropomum (Cuvier, 1881) (Pisces: Characidae) during the reproductive cycle.

This study allowed the characterization of the tambaqui Colossoma macropomum testes structural organization, emphasizing Sertoli and interstitial cells and analyzing morphometrically the Sertoli cell nucleus diameter and the interstitial tissue area during the reproductive cycle. Fragments of tambaqui testes were collected in the following reproductive cycle stages: immature, resting, maturation I and II, mature, and regression, and were histologically processed. The Sertoli cells were found at the periphery of the cysts of germinative lineage cells and the nuclei were shown to be smaller as these cells developed. The interstitial cells were better observed between the seminiferous lobules next to vessels in the interstitial tissue of maturing testes.

Animals↗
PubMed1994

Chromatin and nucleosome organizations and DNA replication of nucleus reassembled in vitro using purified exogenous DNA and Xenopus egg extracts.

It has been demonstrated in the last ten years that the nuclear reassembly may occur in the cell-free systems from frog egg extracts added with exogenous naked DNA. However, there remains an open question: is the cell-free reassembled nucleus structurally similar to the nucleus in the intact cell? That is, does the cell-free reassembled nucleus contain nucleosomes and chromatin? For this issue, we have designed experiments for identifying the internal structures of the cell-free reassembled nucleus. These experiments show that the nucleus reassembled in vitro also contains chromatin which is composed of typical 10 nm nucleosome fibers of "beads-on-a-string", 30 nm filaments and the next higher-order structures. The digestion experiment with the enzyme micrococcal nuclease has demonstrated that the DNA in the nucleosome of the reconstituted chromatin is about 200 base pairs (bp) in length, of which 165 bp may be in the nucleosome particle, and 35 bp may be in the linker between two particles. Prolonging digestion of the 165-bp particle DNA fragment will yield a 146-bp fragment, which may be wounded in the nucleosome core. Experiments also provide evidence that the chromatin reconstitution in the cell-free reassembled nucleus is a progressive process, and that the nucleus can replicate its DNA. Based on these observations, we suppose that the chromatin of the cell-free reassembled nucleus may be structurally and functionally similar to the chromatin of the intact cells.

Animals↗
PubMed2003

Confocal imaging reveals structural detail of the cell nucleus and ascospore formation in lichenized fungi.

A method for visualization of fungal nuclear structures using the DNA specific fluorochrome SYTOX Green and confocal laser scanning microscopy is presented. The staining procedure detects nuclei in different cell types with high contrast. Furthermore, the method permits generation of high-resolution confocal image stacks using optimised scanning conditions. This approach significantly improved visualization of stained fungal nuclear structures. The technique was applied to some lichenized fungi, but can also be used to study similar detail in non-lichenized fungi. In certain cases, incompletely separated chromosome-like structures, heterochromatic material as well as weakly stained nucleolar regions can be seen. In Xanthoria parietina, variation in the nuclear division was observed in developing ascospores. Delayed division after the formation of endospore thickening resulted in the exchange of nuclear material through a narrow isthmus.

Ascomycota↗
PubMed2006

Splicing speckles are not reservoirs of RNA polymerase II, but contain an inactive form, phosphorylated on serine2 residues of the C-terminal domain.

"Splicing speckles" are major nuclear domains rich in components of the splicing machinery and polyA(+) RNA. Although speckles contain little detectable transcriptional activity, they are found preferentially associated with specific mRNA-coding genes and gene-rich R bands, and they accumulate some unspliced pre-mRNAs. RNA polymerase II transcribes mRNAs and is required for splicing, with some reports suggesting that the inactive complexes are stored in splicing speckles. Using ultrathin cryosections to improve optical resolution and preserve nuclear structure, we find that all forms of polymerase II are present, but not enriched, within speckles. Inhibition of polymerase activity shows that speckles do not act as major storage sites for inactive polymerase II complexes but that they contain a stable pool of polymerase II phosphorylated on serine(2) residues of the C-terminal domain, which is transcriptionally inactive and may have roles in spliceosome assembly or posttranscriptional splicing of pre-mRNAs. Paraspeckle domains lie adjacent to speckles, but little is known about their protein content or putative roles in the expression of the speckle-associated genes. We find that paraspeckles are transcriptionally inactive but contain polymerase II, which remains stably associated upon transcriptional inhibition, when paraspeckles reorganize around nucleoli in the form of caps.

Antibodies↗
PubMed2001

Prespliceosomal assembly on microinjected precursor mRNA takes place in nuclear speckles.

Nuclear speckles (speckles) represent a distinct nuclear compartment within the interchromatin space and are enriched in splicing factors. They have been shown to serve neighboring active genes as a reservoir of these factors. In this study, we show that, in HeLa cells, the (pre)spliceosomal assembly on precursor mRNA (pre-mRNA) is associated with the speckles. For this purpose, we used microinjection of splicing competent and mutant adenovirus pre-mRNAs with differential splicing factor binding, which form different (pre)spliceosomal complexes and followed their sites of accumulation. Splicing competent pre-mRNAs are rapidly targeted into the speckles, but the targeting is temperature-dependent. The polypyrimidine tract sequence is required for targeting, but, in itself, is not sufficient. The downstream flanking sequences are particularly important for the targeting of the mutant pre-mRNAs into the speckles. In supportive experiments, the behavior of the speckles was followed after the microinjection of antisense deoxyoligoribonucleotides complementary to the specific domains of snRNAs. Under these latter conditions prespliceosomal complexes are formed on endogenous pre-mRNAs. We conclude that the (pre)spliceosomal complexes on microinjected pre-mRNA are formed inside the speckles. Their targeting into and accumulation in the speckles is a result of the cumulative loading of splicing factors to the pre-mRNA and the complexes formed give rise to the speckled pattern observed.

Cell Nucleus Structures↗
PubMed1999

Stress and the cell nucleus: dynamics of gene expression and structural reorganization.

A growing number of experimental observations reveal that the cell nucleus is functionally compartmentalized yet organized to ensure a dynamic response to events that influence nuclear activities. The cellular and molecular response to physiological and environmental stress induces a rapid and transient change in gene expression associated with major changes in nuclear architecture that impacts on signals involved in cell growth. In this review, we will address the effects of stress on the functional compartmentation of the cell nucleus and the dynamic reorganization of nuclear structures and function.

Animals↗
PubMed1989

Fine structural ribonucleoprotein components of the cell nucleus visualized after spreading and high resolution autoradiography.

The fine structure of the nuclear components was studied following mild lysis of mouse or Drosophila tissue culture cells and spreading of nuclear material. Particular attention was paid to nuclear ribonucleoprotein (RNP) constituents, which were analysed by high resolution autoradiography after [3H]uridine pulse labelling of cells. Comparison with the labelling kinetics of various in situ nuclear RNP constituents described previously suggests strong similarities between in situ constituents and structures observed within spread nuclear components. The present observations suggest that the nucleolar dense fibrillar component, shown previously in ultrathin sections of [3H]uridine-labelled intact cells as carrying rapidly labelled pre-rRNA, in fact consists of highly compacted transcribing ribosomal genes. The growing RNP fibrils appearing in transcription complexes of extranucleolar active genes and the in situ observed perichromatin fibrils also show the same labelling properties. This confirms that the two structures indeed represent the same nucleoplasmic constituents. As for the nuclear structures involved in post-transcriptional events, our observations demonstrate the occurrence of a rapidly labelled RNP fibro-granular network. Its granular elements correspond, in size and perichromatin location, to the perichromatin granules seen in the situ preparations and suggest similarities between the two constituents. The results are discussed in the light of other data providing information on the role of various nuclear structural constituents.

Animals↗