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PubMed2001

Determination of 8-oxoguanine in individual cell nucleus of gamma-irradiated mammalian cells.

8-Oxoguanine, through its ability to mispair bases other than cytosine, is assumed to be one of the most potent premutagenic lesions in nuclear DNA damaged by reactive oxygen radicals. In this study, we examine whether the presence of residual 8-oxoguanine can be detected in mammalian cells after exposure to ionizing radiation. MOLT-4 human leukemia cells and CHO-K1 Chinese hamster cells were acutely irradiated in vitro with 0, 0.2, 0.4, 0.6 and 1.0 Gy gamma radiation at room temperature. The amounts of 8-oxoguanine and total DNA in the cell nucleus were detected by fluorescein-isothiocyanate (FITC)-labeled avidin, which binds specifically and directly to 8-oxoguanine, and propidium iodide, respectively. The intensity ratios between these two fluorescent dyes were then taken as indices to measure the content of 8-oxoguanine within individual cells. We found an apparent dose-dependent increase in the amount of 8-oxoguanine accumulated in cells of both lines. Moreover, the content of 8-oxoguanine decreased from 2 to 20 h after irradiation in CHO-K1 cells, which may reflect the time-dependent repair processes at the 8-oxoguanine lesions. This novel approach may provide a sensitive tool for in situ measurement of 8-oxoguanine in cells or even in the human body after exposure to ionizing radiation.

Animals↗
PubMed2001

Functional architecture in the cell nucleus.

The major functions of the cell nucleus, including transcription, pre-mRNA splicing and ribosome assembly, have been studied extensively by biochemical, genetic and molecular methods. An overwhelming amount of information about their molecular mechanisms is available. In stark contrast, very little is known about how these processes are integrated into the structural framework of the cell nucleus and how they are spatially and temporally co-ordinated within the three-dimensional confines of the nucleus. It is also largely unknown how nuclear architecture affects gene expression. In order to understand how genomes are organized, and how they function, the basic principles that govern nuclear architecture and function must be uncovered. Recent work combining molecular, biochemical and cell biological methods is beginning to shed light on how the nucleus functions and how genes are expressed in vivo. It has become clear that the nucleus contains distinct compartments and that many nuclear components are highly dynamic. Here we describe the major structural compartments of the cell nucleus and discuss their established and proposed functions. We summarize recent observations regarding the dynamic properties of chromatin, mRNA and nuclear proteins, and we consider the implications these findings have for the organization of nuclear processes and gene expression. Finally, we speculate that self-organization might play a substantial role in establishing and maintaining nuclear organization.

Animals↗
PubMed1976

[Studies on endocrine and spermiogenic testis function. III. Relationships between the quality of dietary proteins, testosterone content of the testes and cell nucleus volume of the Leydig cells during postnatal developme-t of rats].

Male Wistar rats, aged 15 days, received different qualities of feed proteins through 80 days (absorbable crude protein-rRP = ten per cent). For experimentation, the animals were subdivded into four groups. The first group was given casein plus four per cent methionine (K), the second maize gluten with amino acid added (M + As), the third maize gluten only (M), and the fourth casein plus four per cent methionine mixed one to three with gelatin (K/G). Live weight increases after ten days of feeding were 34+/-13.9 g (K), 24+/-8.5 g (M + As), 8+/-5.7 g (M), and 0+/-3.6 g (K/G). The same trend was recorded from testicular weight which was measured as well in ten-day intervals. The eight cyclic phases of the germinal epithelium were completely developed as of the 45th day of age in animals on K and M+/-As rations and as rations and as the 95th day of age in animals on K/G ration (followed improvement to 2:3). Spermatide transformation still was a bit differentiated by histological examination of animals on M diet on the 95th day of experimentation. The testosterone levels in testicular tissue were about 220 ng/100 g live weight after 80 days of K or M + As diets, but only 100 ng/100 g live weight after K/G or M feeding. The nuclear volumes of the interstitial cells of Leydig exhibited significant variation (p less than 0.01) between the 35th and 45th days of age, but went stable to approximately 50 mum3, independent of feed protein quality, at the onset of suxual maturity, on the 95th day of age. Complete formation of all eight cyclic phases of the germinal epithelium seems to depend on limiting values relating to testosterone per gram of testis, testicular weight nuclear volume of the interstitial cells of Leydig and live weight.

Animals↗
PubMed1976

[Studies on endocrine and spermiogenic testis function. IV. Relations between the testosterone content of the testes cell nucleus volume of the Leydig cells and rat spermatogenesis (deduced from studies on the effect of the dietary protein quality on the function of the testes)].

The following relations were derived from large-scale testing of feed protein quality and its bearings on testicular function in growing Wistar rats: testicle weights and live weights r = 0.77 for juvenile animals and r = 0.36 for adult animals; nuclear volumes of Leydig's cells to testicle weights r = 0.84 for juvenile animals and r = 0.43 for adult animals; testosterone in testicular tissue, ng/g, to testicle weights r = 0.55 for juvenile animals and r = 0.80 for adult animals; testosterone per live weight, ng/100 g, to nuclear volumes of Leydig's cells r = 0.76 for juvenile animals and r = 0.46 for adult animals. Critical thresholds above which complete spermatogenesis is always ensured may be established for testosterone (50+/-5 ng/100 g live weight) and for the nuclear volume of Leydig's cells (30 mum3). Another conclusions drawn from the above results is that high testosterone levels in the testes of adult animals were not attributable to high testosterone biogenesis of Leydig's cells, as might have been assumed from high activities of that kind recordable from some nuclear volumes.

Animals↗
PubMed2000

Atomic force microscopy of the cell nucleus.

In mammals and plants, the cell nucleus is organized in dynamic macromolecular domains involved in DNA and RNA metabolism. These domains can be visualized by light and electron microscopy and their composition analyzed by using several cytochemical approaches. They are composed of chromatin or ribonucleoprotein structures as interchromatin and perichromatin fibers and granules, coiled bodies, and nuclear bodies. In plants, DNA arrangement defines chromocentric and reticulated nuclei. We used atomic force microscopy to study the in situ structure of the plant cell nucleus. Samples of the plants Lacandonia schismatica and Ginkgo biloba were prepared as for electron microscopy and unstained semithin sections were mounted on glass slides. For comparison, we also examined entire normal rat kidney cells using the same approach. Samples were scanned with an atomic force microscope working in contact mode. Recognizable images of the nuclear envelope, pores, chromatin, and nucleolus were observed. Reticulated chromatin was observed in L. schismatica. Different textures in the nucleolus of G. biloba were also observed, suggesting the presence of nucleolar subcompartments. The observation of nuclear structure in situ with the atomic force microscope offers a new approach for the analysis of this organelle at high resolution.

Animals↗
PubMed2006

Imaging of single mRNA molecules moving within a living cell nucleus.

In eukaryotic cells, pre-mRNAs are transcribed in the nucleus, processed by 5' capping, 3'-polyadenylation, and splicing, and exported to the cytoplasm for translation. To examine the nuclear mRNA transport mechanism, intron-deficient mRNAs of truncated beta-globin and EGFP were synthesized, fluorescently labeled in vitro, and injected into the nucleus of living Xenopus A6 cells. The trajectories of single mRNA molecules in the nucleus were visualized using video-rate confocal microscopy. Approximately half the mRNAs moved by Brownian motion in the nucleoplasm, except the nucleoli, with an apparent diffusion coefficient of 0.2microm(2)/s, about 1/150 of that in water. The slow diffusion could not be explained by simple diffusion obeying the Stokes-Einstein equation, suggesting interactions of the mRNAs with nuclear components. The remaining mRNAs were stationary with an average residence time of about 30s, comparable to the time required for mRNA diffusion from the site of synthesis to nuclear pores.

Active Transport, Cell Nucleus↗
PubMed2002

Identification of PSF as a protein kinase Calpha-binding protein in the cell nucleus.

Protein kinase C (PKC) isoforms are present in the cell nucleus in diverse cell lines and tissues. Since little is known about proteins interacting with PKC inside the cell nucleus, we used Neuro-2a neuroblastoma cells, in which PKCalpha is present in the nucleus, to screen for nuclear binding partners for PKC. Applying overlay assays, we detected several nuclear proteins which bind to PKCalpha. Specificity of binding was shown by its dependence on PKC activation by phorbol ester, calcium, and phosphatidylserine. The PKC-binding proteins were partially purified and analyzed by microsequencing and mass spectrometry. Four proteins could be identified: PTB-associated splicing factor (PSF), p68 RNA helicase, and the heterogeneous nuclear ribonucleoprotein (hnRNP) proteins A3 and L. In the case of PSF, binding to PKC could also be demonstrated in a GST-pull-down assay using GST-PKCalpha, expressed in insect cells. Phosphorylation experiments revealed that PSF is a weak in vitro substrate for PKCalpha.

Amino Acid Sequence↗
PubMed1992

The protein kinase C-related PKC-L(eta) gene product is localized in the cell nucleus.

The tumor promoters phorbol esters are thought to induce changes in cell growth and gene expression by direct activation of protein kinase C (PKC). However, the molecular mechanisms by which PKC molecules transduce signals into the cell nucleus are unknown. In this study, we provide evidence for a direct target for phorbol esters in the nucleus. We demonstrate that the new PKC-related family member, PKC-L, recently isolated by us, is expressed specifically in the cell nucleus. Localization of PKC-L in the cell nucleus is shown both by immunofluorescence staining and by subcellular fractionation experiments of several human cell lines, including the human epidermoid carcinoma line A431. Treatment of these cells by phorbol esters does not induce the down-regulation of PKC-L, in contrast to their effect on classical PKC family members. This is the only PKC isoenzyme described so far that resides permanently and specifically in the cell nucleus. PKC-L may function as an important link in tumor promoting, e.g., as a nuclear regulator of gene expression that changes the phosphorylation state of transcriptional components such as the AP-1 complex.

Cell Nucleus↗
PubMed1979

The toxic effect of double-stranded RNA for interferon-treated cells: evidence for a heterogeneous cellular response and the role of the cell nucleus.

When L929 cells were treated with interferon and subsequently with poly(rI).poly(rC), there was a pronounced toxic effect. Most of the cells lysed, but some survived and grew at the same rate as control cells to yield cells which were as sensitive to the effects of interferon and poly(rI).poly(rC) as the original population. The proportion of surviving cells did not vary with either the cell cycle or the cell density. The treated cells produced interferon and some of the interferon was produced by the resistant cells. Cells which had been X-irradiated before treatment with interferon and poly(rI).poly(rC) behaved similarly so cell division was not necessary for the development of toxicity. The toxic effect also developed when cells were enucleated with the aid of cytochalas in B after treatment with interferon, but not if they were enucleated before treatment. It is concluded that the nucleus is essential for interferon to exert its effect on the cells, but not for the development of cytotoxicity after the addition of poly(rI).poly(rC).

Animals↗
PubMed1995

Modelling of the relationship between cell dimensions and mean electron dose delivered to the cell nucleus: application to five radionuclides used in nuclear medicine.

The mean dose delivered to the cell nucleus by electron emissions of 99Tcm, 123I, 111In, 67Ga and 201Tl was evaluated at the subcellular level. Models were applied assuming uniform distributions of radioactivity throughout the nucleus, the cytoplasm or the cell membrane, allowing computation of the total absorbed fraction, phi and S-values to the cell nucleus as a function of cell dimensions. The graphs of phi plotted according to cell dimensions show that the dose to the cell nucleus strongly depends on the subcellular distribution of radioactivity, the nucleus radius Rnucl and the cytoplasmic thickness e. For a nuclear distribution, phi ranges from 0.1 to 0.35 for the radionuclides studied and S from 0.049 cGy Bq-1 s-1 to 5.503 cGy Bq-1 s-1. In the case of a cell membrane localization, the maximum is obtained for 123I (phi = 0.016). For a cytoplasmic distribution, the maximum is obtained for 201Tl with a value of 0.036. To ease future calculations, third-degree polynomials have been separately fitted to the relationship between the mean absorbed dose to the nucleus for activity accumulated in the nucleus, cytoplasm or surface of the cell membrane. We found a good agreement between our computations and the values obtained by the polynomials. The relative difference between the two methods is always less than 0.7%, 2.8% and 4.5% respectively for nuclear, cell membrane and cytoplasmic distributions.

Cell Membrane↗
PubMed1977

Requirement of cell nucleus for African swine fever virus replication in Vero cells.

The role of the cell nucleus in the development of African swine fever virus in Vero cells has been studied. No viral growth could be detected in enucleated cells under conditions that allow normal development of Sindbis virus. Furthermore, African swine fever virus DNA synthesis was inhibited more than 95% after infection of enucleated Vero cells as compared with normal cells.

African Swine Fever Virus↗
PubMed2002

In situ cell nucleus deformation in tendons under tensile load; a morphological analysis using confocal laser microscopy.

Cell and cell nucleus deformations have been implicated in the mechanotransduction of mechanical loads acting on tissues. While in situ cell nucleus deformation in response to increasing tissue strains has been examined in articular cartilage this phenomenon has not been investigated in tendons. To examine in situ cell nuclei deformation in tendons undergoing tensile strain rat tail tendons were harvested from adult Sprague-Dawley rats and stained with acridine orange to highlight the cell nuclei. The tendons were mounted on a custom-designed, low-load, tensile testing device affixed to the mechanical stage of a confocal laser microscope. Cells within the tendons were isolated for analysis. Images of individual cells were captured at 0% strain as well as sequentially at 2%, 4% and 6% grip-to-grip tendon strain. Digital images of the cell nuclei were then measured in the x (length) and y (height) axis and deformation expressed as a percentage of cell nuclei strain. In addition, centroid-to-centroid distances of adjacent cell nuclei within each image were measured and used to calculate local tissue strain. There was a weak (r2 = 0.34) but significant (p < 0.01) correlation between local tissue strain and cell nucleus strain in the x axis. The results of this study support the hypothesis that in situ cell nucleus deformation does occur during tensile loading of tendons. This deformation may play a significant role in the mechanical signal transduction pathway of this tissue.

Animals↗