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Membranous structures in continuity with the nuclear envelope, in neuroblasts.
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Ultrastructure of the dinoflagellate Polykrikos. II. The nucleus and its connections to the flagellar apparatus.
Electron microscopy of the colonial dinoflagellate Polykrikos kofoidi revealed a nuclear cortex formed of two electron-dense cortical layers directly beneath the nuclear envelope. Nuclear pores were confined to vesicular outpocketings of the nuclear envelope over circular discontinuities in the cortical layers. A conspicuous fibrous ribbon extended from the nucleus to the flagellar apparatus of each zooid. The ribbons resembled in their structure and position the attractophores of termite flagellates. Each flagellar apparatus consisted of two flagella, two elongate axial kinetosomes, an oblique kinetosome, and two roots of markedly different periodicities.
Nucleocytoplasmic transport of plasmid DNA: a perilous journey from the cytoplasm to the nucleus.
Nonviral vectors represent a promising approach for the safe delivery of therapeutic DNA in genetic and acquired human diseases. Before synthetic vector systems can be used for clinical applications, their limited efficacy must be addressed. At the cellular level, successful gene transfer is dependent on several additional factors including DNA uptake, release from the DNA-vector complex, and nucleocytoplasmic transport. This paper reviews the major metabolic and physical impediments that plasmid DNA vectorized by synthetic vectors encounters between the cytosol and the nucleus. Plasmid DNA that escapes the endolysosomal compartment encounters the diffusional and metabolic barriers of the cytoplasm, reducing the number of intact plasmids that reach the nuclear envelope. Nuclear translocation of DNA requires either the disassembly of the nuclear envelope during cell division or active nuclear transport via the nuclear pore complex. In the nucleus, plasmid DNA is relatively stable, but its transcription and its fate during cell division are still debated. A better understanding of the cellular and molecular basis of nonviral gene transfer during nucleocytoplasmic trafficking may provide strategies to overcome those obstacles that limit the efficiency of nonviral gene delivery. We review some of the current methods of gene transfer mediated by synthetic vectors, highlighting systems that exploit our actual knowledge of the nucleocytoplasmic transport of plasmid DNA.
The Turbidity of Cell Nuclei in Suspension: A Complex Case of Light Scattering.
The turbidity of a suspension of cell nuclei isolated from animal tissue homogenates is a complex case of non-Rayleigh scattering. As a first approximation to this system, we have characterized a number of factors that may contribute to the observed turbidity: cation-dependent chromatin condensation, thermal denaturation of chromatin, nuclear shrinking, and changes in the optical properties of the membrane bilayer. Small differences in cation concentration, particularly in the case of divalent cations, lead to large changes in chromatin supramolecular organization, thus to large turbidity effects; thermally-induced changes in turbidity have a similar origin, although they are less pronounced. Under certain circumstances, either salts or heat may induce condensation of chromatin, the latter being connected to the inner side of the nuclear envelope, nuclear shrinking ensues, and this in turn modifies the suspension turbidity. Finally, changes in the physical properties of the lipid bilayers or of the phospholipids in the nuclear envelopes may also have significant effects, though smaller than chromatin changes, in the overall turbidity of the nuclear suspension.
Photoaffinity labelling of a nuclear matrix nucleoside triphosphatase and its modulation in the acute-phase response.
Photoaffinity labelling has been used to identify the major nuclear matrix nucleoside triphosphatase (NTPase) as a 46 kD polypeptide, which appears to represent the same polypeptide photolabelled in nuclear envelope. Nuclear matrix NTPase and its photolabelling were selectively decreased in the acute phase response of rat liver, which also encompasses decreases (30%) in RNA transport in vitro and nuclear envelope NTPase. These results, and quantitative considerations suggest that the NTPase correlatively linked to RNA transport is not solubilized by detergents; it appears to represent a nuclear matrix component.
The A-type lamins: nuclear structural proteins as a focus for muscular dystrophy and cardiovascular diseases.
Mutations in the lamin A (LMNA) gene are associated with the tissue-specific diseases Emery-Dreifuss muscular dystrophy (EDMD), limb girdle muscular dystrophy (LGMD-1B), dilated cardiomyopathy with conduction system disease (DCM-CD), and Dunnigan's familial partial lipodystrophy (FPLD). Lamins A and C, the products of the LMNA gene, are nuclear intermediate filament proteins and are the major structural components of the lamina network that underlies and supports the nuclear envelope. Nuclear fragility and mislocalization of the nuclear envelope protein emerin are two defects induced by a lack of the A-type lamins. These observations reveal that organization and structural integrity of the nucleus are critical factors in the origins of certain dystrophic and cardiovascular diseases.
Endoplasmic reticulum dynamics, inheritance, and cytoskeletal interactions in budding yeast.
The endoplasmic reticulum (ER) in Saccharomyces cerevisiae consists of a reticulum underlying the plasma membrane (cortical ER) and ER associated with the nuclear envelope (nuclear ER). We used a Sec63p-green fluorescent protein fusion protein to study motility events associated with inheritance of cortical ER and nuclear ER in living yeast cells. During M phase before nuclear migration, we observed thick, apparently rigid tubular extensions emanating from the nuclear ER that elongate, undergo sweeping motions along the cell cortex, and shorten. Two findings support a role for microtubules in this process. First, extension of tubular structures from the nuclear ER is inhibited by destabilization of microtubules. Second, astral microtubules, structures that undergo similar patterns of extension, cortical surveillance and retraction, colocalize with nuclear ER extensions. During S and G(2) phases of the cell cycle, we observed anchorage of the cortical ER at the site of bud emergence and apical bud growth. Thin tubules of the ER that extend from the anchored cortical ER display undulating, apparently random movement and move into the bud as it grows. Finally, we found that cortical ER morphology is sensitive to a filamentous actin-destabilizing drug, latrunculin-A, and to mutations in the actin-encoding ACT1 gene. Our observations support 1) different mechanisms and cytoskeletal mediators for the inheritance of nuclear and cortical ER elements and 2) a mechanism for cortical ER inheritance that is cytoskeleton dependent but relies on anchorage, not directed movement.
Looking for nuclear translation using xenopus oocytes.
In eukaryotes transcription and translation takes place in two different compartments separated by the nuclear envelope. Nuclear translation has been reported in several publications, however, all these published results have been criticized, particularly with respect to cytoplasmic contamination of the nuclei. We have investigated the question of nuclear protein synthesis using a different strategy. We microinjected frog oocytes with different DNA and RNA constructs and searched for translation products in nuclei separated from the cytoplasm by microdissection. We have been unable to detect any translation within the nuclei but rather a saturable translation in the perinuclear cytoplasm associated with the isolated nuclei.
Peptide diffusion, protection, and degradation in nuclear and cytoplasmic compartments before antigen presentation by MHC class I.
Antigenic peptides generated by the proteasome have to survive a peptidase-containing environment for presentation by MHC class I molecules. We have visualized the fate and dynamics of intracellular peptides in living cells. We show that peptides are distributed over two different but interconnected compartments, the cytoplasm and the nucleus, and diffuse rapidly through and between these compartments. Since TAP is excluded from the nuclear face of the nuclear envelope, nuclear peptides have to leave the nucleus to contact TAP. Thereby, these peptides encounter cytosolic peptidases that degrade peptides within seconds unless bound to chromatin. Since peptide degradation is far more efficient than translocation, many peptides will be lost for antigen presentation by MHC class I molecules.
The molecular mechanism of transport of macromolecules through nuclear pore complexes.
Trafficking of macromolecules between nuclear and cytoplasmic compartments takes place through the nuclear pore complexes (NPCs) of the nuclear envelope. Nuclear trafficking involves a complex series of interactions between cargo, soluble transport factors (carriers) and nuclear pore proteins (nucleoporins) that are orchestrated by the Ras-family GTPase Ran. The primary role of Ran is probably to establish directionality and to sort molecules to be transported by controlling the interaction between carriers and cargoes, so that they bind in one compartment but dissociate in the other. Translocation of carriers and cargo-carrier complexes through NPCs requires interactions between the carriers and nucleoporins that contain distinctive tandem sequence repeats based on cores rich in glycine and phenylalanine residues that are separated by hydrophilic linkers. Much recent work has focused on these interactions and, in particular, their specificity, regulation and function. Evidence is accumulating that carriers move through the NPC by distinct but overlapping routes using specific subsets of nucleoporins.
Co-localization of apoptosis-regulating proteins in mouse mammary epithelial HC11 cells exposed to TGF-beta1.
TGF-beta1 is an apoptogenic agent for mammary epithelial cells (MEC). The molecular mechanism of the TGF-beta1-induced apoptosis remains, however, obscure. In the present study we used laser scanning cytometry, confocal microscopy and immunogold electron microscopy to analyze the expression, aggregation and co-localization of caspase-8, Bid, Bax and VDAC-1. These proteins are regarded as the most important factors involved in the regulatory phase of TGF-beta1-induced apoptosis. Apoptosis in HC11 mouse MEC manifested with a simultaneous increase in expression and subcellular aggregation of caspase-8, Bid, Bax and VDAC-1. Confocal microscopy revealed a strong pattern of co-localization of examined proteins during both early and late apoptosis. Experiments with double- and triple-staining immunoelectron microscopy showed a co-localization of Bax/Bid, caspase-8/Bax/Bid, and Bax/VDAC-1, on the membranes of mitochondria, Golgi apparatus, rough endoplasmic reticulum, nuclear envelope, nuclear pore, and within the nucleus. In conclusion, the observed pattern of changes in aggregation and subcellular localization of caspase-8, Bid, Bax and VDAC-1 during TGF-beta1-induced apoptosis in HC11 mouse MEC suggests an interaction between these proteins and formation of multimeric complexes on organellar membranes, thus controlling their permeability for intracellular mediators of apoptosis.
A new method for detecting and localizing cell markers endocytosed by fibroblasts in epoxy resin semi-thin sections using scanning electron microscopy combined with energy dispersive X-ray microanalysis after ion-etching.
Cell marking is widely used to examine cell development and differentiation in developmental biology. We developed a new method for localizing cell markers in a semi-thin epoxy section with scanning electron microscopy. Cultured fibroblasts ingesting carbon particles were autologously transplanted into a rabbit transparent ear chamber, 6 mm in diameter and 100 microm in depth. Eight days after the transplantation, tissues in the chamber were fixed and embedded in epoxy resin. Semi-thin sections were cut and stained with toluidine blue. Fibroblasts in connective tissues which contained black spots were observed with a light microscope. These sections were subsequently ion-etched with an ion-coater and coated with platinum. The same fibroblasts were then visualized by secondary electron imaging using a scanning electron microscope. A nucleus with nuclear envelope, nuclear pores, a nucleolus and heterochromatin, mitochondria with cristae and rough endoplasmic reticulum were observed in the fibroblasts. The black spots in the fibroblasts were identified as bright bodies with the scanning electron microscope. The bright bodies were found to be a lump of tiny particles less than 100 nm in diameter. In order to analyse such particles with energy dispersive X-ray microanalysis, ion-etched sections were coated with carbon. X-ray energy spectrometry clearly demonstrated that these were carbon particles, which had been endocytosed by the fibroblast. This suggests that scanning electron microscopy combined with energy dispersive X-ray microanalysis is useful for detecting carbon particles in the cytoplasm at an ultrastructural level in semi-thin epoxy sections subsequent to ion etching and that this method may be applicable to other cell markers, such as gold particles to track cells in the field of cell development and cell differentiation.
[Apoptosis of cultured human trophoblasts induced by tumor necrosis factor-alpha and interferon-gamma].
OBJECTIVE: To investigate the potential role of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in inducing apoptosis of human trophoblast during early pregnancy and its mechanism. METHODS: Human trophoblast of early gestation were cultured in vitro. Having cultured with TNF-alpha and IFN-gamma for 36 hours, their cytotoxic activity was determined by viable cell calculation. Apoptotic morphology was observed under light and electronic microscope. DNA fragment pattern and apoptotic index were analysed by agarose gel electrophoresis and flow cytometer assay (FCM) respectively. Adherent cell analysis and sorting interactive laser cytometer was used to examine the changes of cellular reactive oxygen species (ROS) caused by TNF-alpha. RESULTS: TNF-alpha alone significantly decreased the number of viable cells at the concentration of 1,000, 3,000 and 5,000 U/ml (P < 0.05). While combined with IFN-gamma, TNF-alpha decreased the number of viable cells more markedly. Electronic microscopic examination showed chromatin aggregating beneath the nuclear envelope, nuclear contraction and apoptotic bodies. Agarose gel electrophoresis of fragmented DNA showed a ladder-like pattern. FCM showed that the apoptotic index of trophoblasts was TNF-alpha concentration dependent. Cellular ROS was increased by TNF-alpha. CONCLUSION: TNF-alpha and IFN-gamma could induce apoptosis of human trophoblasts during early pregnancy, partly through the mechanism of ROS.
Lack of binding effect of insulin on RNA synthesis to isolated nuclei.
Insulin stimulates RNA synthesis in the human hepatoma cell line J5. The mechanisms of insulin action on nuclear functions are not fully understood. To assess the possible action of nuclear insulin binding on RNA synthesis, we studied the insulin action by an in vitro transcription system using the nuclei isolated from control cells and insulin-stimulated J5 cells. Insulin binding was done by ligand binding assay. RNA synthesis was also studied in the nuclei treated with insulin in vitro. We found that a large pool of low-affinity binding sites existed in the isolated nuclei preparation without site-to-site interactions. These data suggest that the majority of nuclear insulin binding sites are located inside the nuclear envelope. Nuclear RNA synthesis was stimulated by the insulin (about a 4-fold increase when compared to the control) added to intact cells but not to isolated nuclei. We conclude that insulin stimulates nuclear RNA synthesis via interaction with plasma membrane receptors.
[The mechanisms of the realization of the effect of glucocorticoids in aging].
The interaction of glycocorticoids with serum transport proteins, plasma membranes and rat liver cytoplasmic receptors progressively declines during ontogenesis, reaching its minimum at 24 months of age. Glycocorticoid receptor complexes (GRCs) binding to the rat liver nuclei and their residual fractions as well as the glycocorticoid-induced initiation of RNA-synthesis also decrease with age. The GRCs are shown to be capable of association with nuclear envelope, nuclear matrix and RNA-containing nuclear fraction isolated from the rat liver. The intracellular glycocorticoid receptor recycling requires fresh synthesis of the RNA and protein.
[The formation process of chromatoid body in spermatogenic cell of teleost, Spinibarbus caldwelli (Nichols)].
The formation process of chromatoid body in spermatogenic cell of teleost, Spinibarbus caldwelli (Nichols) was observed with electron microscopy. The chromatoid body was formed in the primary spermatogonium. First, the precursor of chromatoid body adhered to the inner surface of the nuclear envelope. The nuclear envelope where the chromatoid body adhering was destroyed. At the inner side of the precursor of chromatoid body, new nuclear envelope formed. It separated the precursor of chromatoid body from nucleus. The newly formed nuclear envelope was concaved. Thus a hollow appears on the surface of the nucleus. The precursor of chromatoid body gathered in the hollow and condensed into chromatoid body. There were many big gaps on the newly formed nuclear envelope. A little precursor of chromatoid body which had not been separated from the nucleus before comed out of the nucleus through these gaps and into the hollow, where it integrated with the chromatoid body. The way of chromatoid body formation in spermatogenic cell of Spinibarbus caldwelli was different from the way by which nuclear material comes out of the nucleus. It was suggested that there was a different way by which nuclear material could go out of the nucleus. The chromatoid body combined with mitochondria soon after it was formed, and left the hollow. During the development of the spermatogonium, the chromatoid body separated from mitochondria.
Kinetics of internalization and subcellular binding sites for T3 in mouse liver.
The intracellular fate of radiolabeled T3 taken up by mice hepatocytes in vivo was determined at specific time intervals (2-120 min) after injection by quantitative electron microscopic radioautography. Injection of a 200-fold excess of unlabeled T3 together with [125I]-T3 resulted in a more than 90% inhibition of radioactivity detected in hepatocytes. A simple grain density (GD) analysis of radioautograms revealed that a specific labeling (GD > 1) was displayed by only five cell compartments: the plasma membrane, lipid droplets, mitochondria, nuclear envelope and nuclear matrix whereas other compartments were not labeled. Labeled compartments showed distinct changes in the pattern of labeling over time: the plasma membrane was labeled only 2 min after T3 injection, whereas labeling of the nuclear envelope was high at 2 min, decreased at 15 min and progressively increased to maximal measured levels at 120 min. After a lag time of 30 min, nuclear matrix labeling increased progressively with time. Mitochondrial labeling was found to be specific at any time point studied but showed no change over time. These ultrastructural data have been confirmed in vitro by the interaction of T3 with plasma membrane, nuclear membrane, nuclear matrix and mitochondria by real-time biospecific interaction analysis in a BIAcore system. These results demonstrate that T3 binds to hepatocytes before internalization, is transported both to mitochondria and to the nuclear envelope and translocated into the nuclear matrix.