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Results for “nuclear mechanics”

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At least 19 recordsLinked to original sources
PubMed2005

The nuclear membrane and mechanotransduction: impaired nuclear mechanics and mechanotransduction in lamin A/C deficient cells.

Mutations in the lamin A/C gene cause a variety of human diseases including Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy and Hutchinson-Gilford progeria syndrome. The tissue specific effects of lamin mutations are unclear, in part because the function of lamin A/C is incompletely defined, but the many muscle specific phenotypes suggest that defective lamin A/C could increase cellular mechanical sensitivity. Lamin A/C deficient fibroblasts were subjected to mechanical strain to measure nuclear mechanical properties and strain-induced signalling. We found that lamin A/C deficient fibroblasts are characterized by impaired nuclear mechanics and mechanotransduction, reflected by increased nuclear deformations, increased nuclear fragility, attenuated expression of mechanosensitive genes, and impaired transcriptional activation, leading to impaired viability of mechanically strained cells. Lamins and other nuclear envelope proteins can thus affect several levels of the mechanotransduction cascade, altering nuclear and cytoskeletal mechanics as well as playing an important role in mechanically activated gene regulation. Individual mutations in the lamin A/C gene could potentially selectively interfere with any of these functions, explaining the tissue-specific effects observed in the laminopathies.

Animals↗
PubMed2004

Lamin A/C deficiency causes defective nuclear mechanics and mechanotransduction.

Mutations in the lamin A/C gene (LMNA) cause a variety of human diseases including Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy, and Hutchinson-Gilford progeria syndrome. The tissue-specific effects of lamin mutations are unclear, in part because the function of lamin A/C is incompletely defined, but the many muscle-specific phenotypes suggest that defective lamin A/C could increase cellular mechanical sensitivity. To investigate the role of lamin A/C in mechanotransduction, we subjected lamin A/C-deficient mouse embryo fibroblasts to mechanical strain and measured nuclear mechanical properties and strain-induced signaling. We found that Lmna-/- cells have increased nuclear deformation, defective mechanotransduction, and impaired viability under mechanical strain. NF-kappaB-regulated transcription in response to mechanical or cytokine stimulation was attenuated in Lmna-/- cells despite increased transcription factor binding. Lamin A/C deficiency is thus associated with both defective nuclear mechanics and impaired mechanically activated gene transcription. These findings suggest that the tissue-specific effects of lamin A/C mutations observed in the laminopathies may arise from varying degrees of impaired nuclear mechanics and transcriptional activation.

Animals↗
PubMed2006

Lamins A and C but not lamin B1 regulate nuclear mechanics.

Mutations in the nuclear envelope proteins lamins A and C cause a broad variety of human diseases, including Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy, and Hutchinson-Gilford progeria syndrome. Cells lacking lamins A and C have reduced nuclear stiffness and increased nuclear fragility, leading to increased cell death under mechanical strain and suggesting a potential mechanism for disease. Here, we investigated the contribution of major lamin subtypes (lamins A, C, and B1) to nuclear mechanics by analyzing nuclear shape, nuclear dynamics over time, nuclear deformations under strain, and cell viability under prolonged mechanical stimulation in cells lacking both lamins A and C, cells lacking only lamin A (i.e. "lamin C-only" cells), cells lacking wild-type lamin B1, and wild-type cells. Lamin A/C-deficient cells exhibited increased numbers of misshapen nuclei and had severely reduced nuclear stiffness and decreased cell viability under strain. Lamin C-only cells had slightly abnormal nuclear shape and mildly reduced nuclear stiffness but no decrease in cell viability under strain. Interestingly, lamin B1-deficient cells exhibited normal nuclear mechanics despite having a significantly increased frequency of nuclear blebs. Our study indicates that lamins A and C are important contributors to the mechanical stiffness of nuclei, whereas lamin B1 contributes to nuclear integrity but not stiffness.

Animals↗
PubMed2004

Nuclear mechanisms of hypoxic cerebral injury in the newborn.

In early studies, we demonstrated that cerebral tissue hypoxia leads to N-methyl-D-aspartate receptor modification and results in increased intracellular Ca2+. Our subsequent studies have demonstrated an alteration in nuclear Ca2+ influx mechanisms and an increase in the nuclear Ca2+ influx after hypoxia. The hypoxia induced nuclear Ca2+ influx increase correlated in a curvilinear function with the increase in the degree of cerebral tissue hypoxia. The activity of nuclear membrane high-affinity Ca2+-ATPase also increased with the increase in cerebral hypoxia. The expression of the proapototic protein Bax increased as an inverse function with cerebral tissue ATP and phosphocreatine concentrations. However,the expression of the antiapoptotic protein Bcl-2 did not increase after hypoxia. Cerebral tissue hypoxia also led to the activation of caspases 3, 8, and 9. Furthermore, our studies demonstrated that the fragmentation of neuronal genomic DNA increased with increase in degree of cerebral tissue hypoxia. Studies presented in this article elucidate nuclear Ca2+ influx and nuclear Ca2+-mediated mechanisms, including signal transduction, apoptotic gene transcription,caspase activation, and nuclear DNA fragmentation, that result in hypoxic neuronal injury in the newborn brain.

Animals↗
PubMed2006

Nucleic acid binding agents exert local toxic effects on neurites via a non-nuclear mechanism.

The mechanism by which drugs that target nucleic acids cause neurotoxicity is not well described. We characterized the neurotoxicity of Hoechst 33342 (bis-benzimide), a common cell permeable nuclear dye, in primary neuronal cultures. The mechanism of cell death was not apoptotic, as death is rapid, not accompanied by typical nuclear morphological changes, and is insensitive to inhibitors of transcription, translation and caspase activity. In addition, free-radical scavenging agents failed to attenuate cell death, and damage was not accompanied by mitochondrial dysfunction. Neuronal processes of cells exposed to Hoechst 33342 display dramatic fragmentation prior to cell death. When this compound was applied selectively to the distal axons of sympathetic neurons grown in compartmented cultures, the distal axons were destroyed. However, the proximal processes present in the cell body compartment were spared, demonstrating direct axonal toxicity rather than a remote effect of nuclear dysfunction. Other cell-permeable nucleic acid binding dyes similarly caused rapid dendritic and axonal toxicity. The hypothesis that these nucleic acid binding dyes target RNA localized to dendrites and axons is supported by observations that RNaseV1 induced similar, rapid neurite fragmentation. We conclude that the neurotoxic effects of nucleic acid binding compounds are mediated, at least in part, by direct neurite injury, which does not require involvement of the cell body and nucleus.

Animals↗
PubMed1989

Regulation of human argininosuccinate synthetase gene: induction by positive-acting nuclear mechanism in canavanine-resistant cell variants.

Nonhepatic human cell variants resistant to the arginine analog, canavanine, express argininosuccinate synthetase (AS) mRNA at levels 200-fold higher than parental cells without amplification of AS gene sequences. In this report we show that this regulation occurs in the nucleus prior to polyadenylation of AS precursor RNA and occurs through a positive-acting mechanism operating in canavanine-resistant cells. The half-life of cytoplasmic AS mRNA was estimated by blocking cellular transcription with actinomycin D. In both parental and canavanine-resistant variants of RPMI 2650 cells, the AS mRNA decayed with a half-life of 12-24 h, showing that cytoplasmic mRNA stabilization was not involved in this regulation. Quantification of AS RNA following cell fractionation showed that AS precursor RNA was present at greatly elevated amounts in the nuclei of canavanine-resistant cells. Similar results were obtained when nonpolyadenylated RNA was examined. Thus, the mechanism underlying high expression of AS mRNA in canavanine-resistant cells is an early nuclear event, and the processes of polyadenylation and transport of RNA to the cytoplasm are not involved. Intraspecific somatic cell hybrids were constructed to test whether the induction of AS mRNA was due to a gain of a function in canavanine-resistant cells or to a loss of a function in parental cells. Quantification of AS mRNA in hybrid cell lines showed that such cells contained high levels similar to those found in the canavanine-resistant parent. These findings show that the induction of AS mRNA is due to a positive-acting mechanism operating in the nucleus of canavanine-resistant cells.

Argininosuccinate Synthase↗
PubMed1997

Growth factor regulation of cell growth and proliferation in the nervous system. A new intracrine nuclear mechanism.

This article discusses a novel intracrine mechanism of growth-factor action in the nervous system whereby fibroblast growth factor-2 (FGF-2) and its receptor accumulate in the cell nucleus and act as mediators in the control of cell growth and proliferation. In human and rat brain the levels and subcellular localization of FGF-2 differ between quiescent and reactive astrocytes. Quiescent cells express a low level of FGF-2, which is located predominantly within the cytoplasm. In reactive astrocytes, the expression of FGF-2 increases and the proteins are found in both the cytoplasm and nucleus. In glioma tumors, FGF-2 is overexpressed in the nuclei of neoplastic cells. Similar changes in FGF-2 expression and localization are found in vitro. The nuclear accumulation of FGF-2 reflects a transient activation of the FGF-2 gene by potentially novel transactivating factors interacting with an upstream regulatory promoter region. In parallel with FGF-2, the nuclei of astrocytes contain the high-affinity FGF-2 receptor, FGFR1. Nuclear FGFR1 is full length, retains kinase activity, and is localized within the nuclear interior in association with the nuclear matrix. Transfection of either FGF-2 or FGFR1 into cells that do not normally express these proteins results in their nuclear accumulation and concomitant increases in cell proliferation. A similar regulation of nuclear FGF-2 and FGFR1 is observed in neural crestderived adrenal medullary cells and of FGF-2 in the nuclei of cerebellar neurons. Thus, the regulation of the nuclear content of FGF-2 and FGFR1 could serve as a novel mechanism controlling growth and proliferation of glial and neuronal cells.

Animals↗
PubMed2005

Early spindle assembly in Drosophila embryos: role of a force balance involving cytoskeletal dynamics and nuclear mechanics.

Mitotic spindle morphogenesis depends upon the action of microtubules (MTs), motors and the cell cortex. Previously, we proposed that cortical- and MT-based motors acting alone can coordinate early spindle assembly in Drosophila embryos. Here, we tested this model using microscopy of living embryos to analyze spindle pole separation, cortical reorganization, and nuclear dynamics in interphase-prophase of cycles 11-13. We observe that actin caps remain flat as they expand and that furrows do not ingress. As centrosomes separate, they follow a linear trajectory, maintaining a constant pole-to-furrow distance while the nucleus progressively deforms along the elongating pole-pole axis. These observations are incorporated into a model in which outward forces generated by zones of active cortical dynein are balanced by inward forces produced by nuclear elasticity and during cycle 13, by Ncd, which localizes to interpolar MTs. Thus, the force-balance driving early spindle morphogenesis depends upon MT-based motors acting in concert with the cortex and nucleus.

Actins↗
PubMed1992

Nuclear mechanisms mediate rhythmic changes in vasopressin mRNA expression in the rat suprachiasmatic nucleus.

Vasopressin (VP) gene expression in the rat suprachiasmatic nucleus (SCN) is subject to a cyclical mode of regulation which is indicative of a close association with the circadian clock intrinsic to this area of the hypothalamus. Previous studies show that both the amount and size (due to differential polyadenylation) of VP mRNA are reduced during the dark phase of the daily cycle. We have now identified the cellular site wherein these changes are mediated. By transcriptional run-on analysis of nuclei isolated at different time points from the SCN we have shown that an attenuation of transcriptional activity can account for the dark-phase reduction in VP mRNA levels; by comparison with other genes expressed in this tissue, a significant, VP gene-specific reduction was observed which resulted in dark-phase transcriptional activity at 30% of light-phase activity (P less than 0.005). A similar diurnal variation was not found in the supraoptic nucleus. In addition, by Northern analysis of sub-cellular RNA pools, we have demonstrated that the smaller, dark-phase-specific VP RNA species is located, in abundance, within the nuclear fraction. These results provide clear evidence that the cyclical changes in SCN VP mRNA expression are primarily regulated within the nucleus, indicating that any potential regulation in the cytoplasm is of secondary importance. Further analysis of the molecular components which mediate the cyclical changes in transcriptional activity of the VP gene may identify fundamental aspects of neuronal timing mechanisms.

Animals↗
PubMed1982

Enhancement of altered-cell foci in baby mouse skin cultures by antitubulin treatment: nuclear mechanisms.

When primary baby mouse skin (BMS) cultures were subcultured for 48 hours into media containing 10(-6) to 10(-7) M colchicine or demecolcine, the number of altered cell foci appearing after 3-4 weeks' maintenance at 36 degrees C was substantially enhanced over drug-free controls. This applied whether or not the primary cultures had been irradiated with white fluorescent light. The additional presence of cytochalasin D and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) sometimes improved and sometimes partly suppressed the enhancing effect of the antitubulin drugs, and these drugs were omitted for reproducible focus enhancement. The enhancement depended on passage through DNA synthesis in presence of colchicine, which did not prevent concurrent or subsequent DNA synthesis but induced a substantial proportion (greater than 33%) to replicate in the tetraploid (4n to 8n) chromosome configuration. Another effect was to induce widespread asymmetric nuclear division, allowing the potential for chromosome loss. All these effects occurred within the first one or few cell cycles after removal of the antitubulin drugs. The results suggest that the generation of tetraploidy perhaps followed by chromosome loss may be an important factor in the rapid induction of altered cell foci. Pre-existing DNA damage is another important factor.

Animals↗
PubMed2003

ANChors away: an actin based mechanism of nuclear positioning.

Mechanisms for nuclear migration and nuclear anchorage function together to control nuclear positioning. Both tubulin and actin networks play important roles in nuclear positioning. The actin cytoskeleton has been shown to position nuclei in a variety of systems from yeast to plants and animals. It can either act as a stable skeleton to anchor nuclei or supply the active force to move nuclei. Two C. elegans genes and their homologues play important roles in these processes. Syne/ANC-1 anchors nuclei by directly tethering the nuclear envelope to the actin cytoskeleton, and UNC-84/SUN functions at the nuclear envelope to recruit Syne/ANC-1.

Actin Cytoskeleton↗
PubMed2006

Which mechanism for nuclear import of plasmid DNA complexed with polyethylenimine derivatives?

BACKGROUND: To investigate the nuclear import mechanism of plasmid/polyethylenimine (PEI) derivative complexes and the putative nuclear targeting of therapeutic genes by the use of oligosaccharides, we have studied the nuclear import of plasmid DNA complexed either with PEI or with lactosylated PEI (Lac-PEI) in cystic fibrosis human airway epithelial cells ( summation operatorCFTE29o- cells). METHODS AND RESULTS: Cells were synchronized by a double-thymidine block protocol and gene transfer efficiency was evaluated: Lac-PEI- and PEI-mediated gene transfer was greatly increased when cells have undergone mitosis during the course of transfection. However, both types of complexes were able to transfect some growth-arrested cells. When the nuclear import of plasmid/Lac-PEI or plasmid/unsubstituted PEI complexes was studied in digitonin-permeabilized cells, the nuclear uptake of both types of complexes did not follow the classic pathway of nuclear localization sequence (NLS)-containing proteins and lactose residues did not act as a nuclear localization signal. CONCLUSIONS: Our results show that for complexes made with PEI derivatives, the major route for plasmid DNA nuclear entry is a passive nuclear importation during mitosis when the nuclear membrane temporarily breaks down. However, albeit to a lesser extent as that observed in dividing cells, a plasmid DNA importation also occurs in nondividing cells by a yet unknown mechanism.

Active Transport, Cell Nucleus↗
PubMed1998

Mechanisms of nuclear positioning.

The mechanisms underlying two types of microtubule-dependent nuclear positioning are discussed. 'MTOC-dependent nuclear positioning' occurs when a nucleus is tightly associated with a microtubule organizing center (MTOC). 'Nuclear tracking along microtubules' is analogous to the motor-driven motility of other organelles and occurs when the nucleus lacks an associated MTOC. These two basic types of microtubule-dependent nuclear positioning may cooperate in many proliferating animal cells to achieve proper nuclear positioning. Microtubule polymerization and dynamics, motor proteins, MAPs and specialized sites such as cortical anchors function to control nuclear movements within cells.

Animals↗
PubMed2001

Nuclear transport mechanisms.

The term nuclear transport, refers to the movement of a large variety of macromolecules both into and out of the nucleus. Transport must be extremely selective, yet also very efficient. A single type of channel, the nuclear pore complex, mediates all movement across the nuclear envelope. Selectivity is achieved through the use of families of soluble factors that target substrates for import and export and deliver them to their appropriate intracellular destinations. We now have a fairly detailed understanding of the basic mechanisms of protein import into the nucleus. Many of these same principles can be applied to protein export and perhaps RNA export. This review will summarize the current status of what is known about various transport pathways and highlight the questions that remain to be answered.

Active Transport, Cell Nucleus↗