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PubMed1993

Reconstitution of nuclear protein transport with semi-intact yeast cells.

We have developed an in vitro nuclear protein import reaction from semi-intact yeast cells. The reaction uses cells that have been permeabilized by freeze-thaw after spheroplast formation. Electron microscopic analysis and antibody-binding experiments show that the nuclear envelope remains intact but the plasma membrane is perforated. In the presence of ATP and cytosol derived from yeast or mammalian cells, a protein containing the nuclear localization sequence (NLS) of SV40 large T-antigen is transported into the nucleus. Proteins with mutant NLSs are not imported. In the absence of cytosol, binding of NLS-containing proteins occurs at the nuclear envelope. N-ethylmaleimide treatment of the cytosol as well as antibodies to the nuclear pore protein Nsp1 inhibit import but not binding to the nuclear envelope. Yeast mutants defective in nuclear protein transport were tested in the in vitro import reaction. Semi-intact cells from temperature-sensitive nsp1 mutants failed to import but some binding to the nuclear envelope was observed. On the other hand, no binding and thus no import into nuclei was observed in semi-intact nsp49 cells which are mutated in another nuclear pore protein. Np13 mutants, which are defective for nuclear protein import in vivo, were also deficient in the binding step under the in vitro conditions. Thus, the transport defect in these mutants is at the level of the nucleus and the point at which nuclear transport is blocked can be defined.

Antigens, Polyomavirus Transforming↗

PubMed1991

Effects of 6-dimethylaminopurine on microtubules and putative intermediate filaments in sea urchin embryos.

The effects of 6-dimethylaminopurine (6-DMAP) (a putative phosphorylation inhibitor) on the state of assembly of microtubules and intermediate filaments have been studied during the first cell cycle of the sea urchin Strongylocentrotus droebachiensis. Changes in the spatial organization of cytoskeletal structures were studied by indirect immunofluorescence with anti-tubulin and anti-IFa antibodies. The rates and patterns of protein phosphorylation in control and treated eggs were also investigated. The transfer of fertilized eggs to 600 microM 6-DMAP within 4 min following insemination inhibits pronuclear migration and syngamy. This also prevents male pronuclear decondensation, while chromatin condensation and nuclear envelope breakdown do not occur in the female pronucleus. Immunolabeling with anti-tubulin antibodies reveals the presence of cortical microtubules as early as 15 min after fertilization in both control and treated eggs. However, no sperm astral microtubules could be detected in the treated eggs. At later stages, from syngamy (40 min) up to nuclear envelope breakdown (90 min), 6-DMAP affects neither cortical microtubule organization nor the state of chromatin condensation but it precludes nuclear envelope breakdown and entry into mitosis. Treatment of the fertilized eggs after nuclear envelope breakdown induces permanent chromosome decondensation and premature disappearance of the mitotic apparatus. This last event involves disruption of the spatial organization of both microtubules and putative intermediate filaments. Quantitative measurements of protein phosphorylation show that 6-DMAP efficiently and reversibly inhibits 32P incorporation into proteins. Qualitative analysis of the autoradiograms of 32P-labeled proteins separated by SDS-PAGE reveals that a major protein band, migrating with an apparent molecular weight of 31 x 10(3)Mr, is specifically dephosphorylated in eggs treated with 6-DMAP. This study suggests that protein phosphorylation is required for sperm aster microtubule growth and migration, but not for cortical microtubule polymerization. It also strengthens the hypothesis that, in sea urchin eggs, putative intermediate filaments are tightly associated with spindle microtubules. Finally, it confirms that inhibiting protein phosphorylation before nuclear envelope breakdown reversibly prevents the entry into mitosis.

Adenine↗

PubMed1991

Changes in the nuclear structure in the radiation-sensitive CHO mutant cell, xrs-5.

The structural organization of the cell nucleus was investigated by transmission electron microscopy in the radiosensitive Chinese hamster ovary (CHO) cell mutant, xrs-5 (D0 = 45 cGy), relative to parental K1 cells (D0 = 200 cGy). In 99% of all xrs-5 cells, the outer layer of the nuclear envelope was separated from the inner layer, while 96% of K1 cells had closely apposed layers. This separation of the inner and outer layers of the nuclear envelope in xrs-5 cells was not explained by an increased susceptibility of xrs-5 cells to osmotically induced changes because (1) xrs-5 cells retained the altered nuclear periphery even when several different fixation protocols were used and (2) xrs-5 cells were not more susceptible to cell lysis as measured by trypan blue dye exclusion or by the extracellular presence of lactate dehydrogenase. The difference in the morphological organization in the nuclear periphery of xrs-5 cells correlated with the radiation sensitivity of the cells; xrs-5 cells which spontaneously reverted to a radiation sensitivity similar to that of K1 cells also reverted to a nuclear morphology similar to that of K1 cells. The inner and outer layers of the nuclear envelope were retained in nuclear scaffolds isolated from K1 and xrs-5 cells, indicating that components of the nuclear periphery are part of the nuclear scaffold. These data show that xrs-5 cells have an altered nuclear periphery which correlates with the radiation sensitivity of the cells. The separation of the layers of the nuclear envelope may represent an altered template for repair of DNA damage at the nuclear scaffold and thus may play a role in the defective repair of X-ray-induced DNA double-strand breaks in xrs-5 cells.

Animals↗

PubMed1956

Studies on nuclei using correlated cytochemical, light, and electron microscope techniques.

In this paper, a procedure for correlating electron microscope and light microscope cytochemical studies using immediately adjacent serial thin and thick sections has been described and discussed. This technique, combined with the Feulgen reaction for DNA, has been of particular value in framing and answering both general and specific questions about the nucleus. The results may be summarized as follows:- Apparent nuclear homogeneity in the electron microscope is not due to loss of DNA as evidenced by positive Feulgen reactions in such nuclei. Arrangement of Feulgen-positive material in chromosomes, heterochromatin, perinuclear and perinucleolar chromatin, etc., is similar to that customarily observed in the light microscope but this is not necessarily reflected in a cursory survey of the electron image. Careful comparison of light and electron images shows that fine differences in structure are associated with chromatin localization. Primary spermatocyte prophase chromosomes of crayfish have been positively identified by their Feulgen-positive nature. Core-like axial structures in such chromosomes have been observed (9) and are described further. A remarkable feature of spermiogenesis in the crayfish is an elaboration of the nuclear envelope of the spermatid accompanying the formation of what becomes a mass of convoluted membranes in the sperm. In the spermatid, perinuclear chromatin follows outpocketings of the nuclear envelope into the cytoplasm. In the early sperm, on the other hand, although the nuclear envelope is continuous with the system of convoluted membranes, the chromatin is distinct from it and is retained in the nucleus proper by some mechanism independent of the nuclear envelope. None of the above observations was apparent from the electron microscope images alone; they were possible only by virtue of the correlated cytochemical and electron microscope study of adjacent sections. The successful use of other cytochemical tests, such as the PAS reaction for certain carbohydrates, in such correlated studies is also described.

Cell Nucleus↗

PubMed1969

Negative staining and adenosine triphosphatase activity of annulate lamellae of newt oocytes.

Semi-isolated annulate lamellae were prepared from single newt oocytes (Triturus alpestris) by a modified Callan-Tomlin technique. Such preparations were examined with the electron microscope, and the negative staining appearance of the annulate lamellae is described. The annulate lamellae can be detected either adhering to the nuclear envelope or being detached from it. Sometimes they are observed to be connected with slender tubular-like structures interpreted as parts of the endoplasmic reticulum. The results obtained from negative staining are combined with those from sections. Especially, the structural data on the annulate lamellae and the nuclear envelope of the very same cell were compared. Evidence is presented that in the oocytes studied the two kinds of porous cisternae, namely annulate lamellae and nuclear envelope, are markedly distinguished in that the annulate lamellae exhibit a much higher pore frequency (generally about twice that found for the corresponding nuclear envelope) and have also a relative pore area occupying as much as 32% to 55% of the cisternal surface (compared with 13% to 22% in the nuclear envelopes). The pore diameter and all other ultrastructural details of the pore complexes, however, are equivalent in both kinds of porous cisternae. Like the annuli of the nuclear pore complexes of various animal and plant cells, the annuli of the annulate lamellae pores reveal also an eightfold symmetry of their subunits in negatively stained as well as in sectioned material. Furthermore, the annulate lamellae are shown to be a site of activity of the Mg-Na-K-stimulated ATPase.

Adenosine Triphosphatases↗

PubMed1993

The role of CaaX-dependent modifications in membrane association of Xenopus nuclear lamin B3 during meiosis and the fate of B3 in transfected mitotic cells.

Recent evidence shows that the COOH-terminal CaaX motif of lamins is necessary to target newly synthesized proteins to the nuclear envelope membranes. Isoprenylation at the CaaX-cysteine has been taken to explain the different fates of A- and B-type lamins during cell division. A-type lamins, which loose their isoprenylation shortly after incorporation into the lamina structure, become freely soluble upon mitotic nuclear envelope breakdown. Somatic B-type lamins, in contrast, are permanently isoprenylated and, although depolymerized during mitosis, remain associated with remnants of nuclear envelope membranes. However, Xenopus lamin B3, the major B-type lamin of amphibian oocytes and eggs, becomes soluble after nuclear envelope breakdown in meiotic metaphase. Here we show that Xenopus lamin B3 is permanently isoprenylated and carboxyl methylated in oocytes (interphase) and eggs (meiotic metaphase). When transfected into mouse L cells Xenopus lamin B3 is integrated into the host lamina and responds to cell cycle signals in a normal fashion. Notably, the ectopically expressed Xenopus lamin does not form heterooligomers with the endogenous lamins as revealed by a coprecipitation experiment with mitotic lamins. In contrast to the situation in amphibian eggs, a significant portion of lamin B3 remains associated with membranes during mitosis. We conclude from these data that the CaaX motif-mediated modifications, although necessary, are not sufficient for a stable association of lamins with membranes and that additional factors are involved in lamin-membrane binding.

Amino Acid Sequence↗

PubMed1980

Hepatic granulomas induced by glucan. An ultrastructural and peroxidase-cytochemical study.

Granulomas were induced in rat liver by the injection of glucan, a beta-1,30-polyglucose with an activating effect on macrophages. The livers were fixed by perfusion with glutaraldehyde and processed for cytochemical localization of peroxidase (PO) as well as for scanning and transmission electron microscopy. By light microscopy the granulomas appeared as spherical cell clusters located throughout the liver parenchyma. They exhibited strong PO activity at the periphery with weak to negative reaction at the center. Most granulomas were in direct continuity with adjacent sinusoids. Morphometry revealed that the volume of granulomas increased to about 10 per cent of the total parenchymal volume at 10 days after glucan treatment, decreasing to less than 2% at 90 days. By scanning electron microscopy most cells at the periphery of granulomas were covered with numerous blebs and ruffles, the typical surface features of activated macrophages. By transmission electron microscopy the typical granulomas consisted of mononuclear phagocytes, giant cells, and a few lymphocytes. The phagocytes, as identified by phagocytosis of glucan, exhibited three distinct PO patterns: (1) strong PO activity in the nuclear envelope and endoplasmic reticulum with no activity in cytoplasmic granules; (2) weak or absent reaction in nuclear envelope and endoplasmic reticulum with no PO-positive granules in cytoplasm; and (3) absent reaction in nuclear envelope and endoplasmic reticulum but with a few strongly stained cytoplasmic granules. The first cell type, resembling Kupffer cells, was found mainly at the granuloma periphery. The second cell type, identified ultrastructurally as epithelioid cells, and the third cell type, with PO features of monocytes, were found mainly in the center of granulomas. The multinucleated giant cells which were also present in the center of granulomas exhibited weak to negative PO reaction in nuclear envelope and endoplasmic reticulum and contained large numbers of glucan particles. These observations suggest that most cells in the center of the granulomas, including the giant cells, are derived from blood monocytes. The mononuclear phagocytes at the periphery, on the other hand, seem to be for the most part former Kupffer cells.

Animals↗

PubMed1976

[Electron-microscopic study of the nuclear membrane of the PKEV cells during mitosis. 1. The breakdown of the nuclear membrane (prophase, prometaphase, metaphase)].

An ultrastructural study on dividing PKEV cells provided a possibility to distinguish between certain stages of their desintegration. The changes preceding fragmentation of the nuclear envelope commence with desorganization of its structural components: vanishing of granular peripherial chromatin layer; appearance of the pores without central granules; formation of deep invaginations of the nuclear membranes. The desintegration of the nuclear envelope starts from the disapearance of many pores and the appearance of perforations almost of the same size. Simultaneously, the number of polysomes is reduced on the outer membrane of the nuclear envelope and in the cytoplasm. Specific features of the nuclear envelope being lost it becomes undistinguishable from the reticulum elements. On serial sections, no contacts were observed between chromosomes and membranous elements.

Animals↗

PubMed2006

Studying nuclear disassembly in vitro using Xenopus egg extract.

Xenopus egg extract provides an extremely powerful approach in the study of cell cycle regulated aspects of nuclear form and function. Each egg contains enough membrane and protein components to support multiple rounds of cell division. Remarkably, incubation of egg extract with DNA in the presence of an energy regeneration system is sufficient to induce formation of a nuclear envelope around DNA. In addition, these in vitro nuclei contain functional nuclear pore complexes, which form de novo and are capable of supporting nucleocytoplasmic transport. Mitotic entry can be induced by the addition of recombinant cyclin to an interphase extract. This initiates signaling that leads to disassembly of the nuclei. Thus, this cell-free system can be used to decipher events involved in mitotic remodeling of the nuclear envelope such as changes in nuclear pore permeability, dispersal of membrane, and disassembly of the lamina. Both general mechanisms and individual players required for orchestrating these events can be identified via biochemical manipulation of the egg extract. Here, we describe a procedure for the assembly and disassembly of in vitro nuclei, including the production of Xenopus egg extract and sperm chromatin DNA.

Animals↗

PubMed2001

[Inositol 1,4,5-triphosphate receptors (IP(3)Rs) in myocardial nuclei involved in pressure overload-induced hypertrophy of rat heart].

In order to clarify the importance of nuclear IP(3)Rs in the development of myocardial hypertrophy, a hypertensive rat model was established by abdominal aortic constriction, and velocity and isopyknic gradient centrifugation was employed to fractionate the cardiac nuclei. The maximal number of binding sites (B(max)) and dissociation constant (Kd) of IP(3) to the nuclear envelopes were measured by [(3)H] IP(3) binding assay. The existence of IP(3)Rs on myocardial nuclear envelope was confirmed. [Ca(2+)] inhibited [(3)H] IP(3) binding to its receptors in cardiac nuclear envelopes in a concentration-dependent way. Phosphorylation by CaM and endogenous PKC decreased B(max) of nuclear IP(3) receptors. B(max) and Kd of nuclear IP(3)Rs were increased by 1.217 (P<0.01) and by 2.149-fold (P<0.01) respectively in hypertrophic myocardium as compared with those of the control. The above results suggest that IP(3)Rs exist in myocardial nuclei and are down regulated by CaM, PMA and free Ca(2+). The increase of the binding sites of IP(3)Rs in the nuclear envelopes and the decrease of their affinity might play importment roles in the development of overload induction of cardiac hypertrophy.

Animals↗

PubMed1983

Intranuclear membranes and the formation of the first meiotic spindle in Xenos peckii (Acroschismus wheeleri) oocytes.

The ultrastructure of spindle formation during the first meiotic division in oocytes of the Strepsipteran insect Xenos peckii Kirby (Acroschismus wheeleri Pierce) was examined in serial thick (0.25-micron) and thin sections. During late prophase the nuclear envelope became extremely convoluted and fenestrated. At this time vesicular and tubular membrane elements permeated the nucleoplasm and formed a thin fusiform sheath, 5-7 micron in length, around each of the randomly oriented and condensing tetrads. These membrane elements appeared to arise from the nuclear envelope and/or in association with annulate lamellae in the nuclear region. All of the individual tetrads and their associated fusiform sheaths became aligned within the nucleus subsequent to the breakdown of the nuclear envelope. Microtubules (MTs) were found associated with membranes of the meiotic apparatus only after the nuclear envelope had broken down. Kinetochores, with associated MTs, were first recognizable as electron-opaque patches on the chromosomes at this time. The fully formed metaphase arrested Xenos oocyte meiotic apparatus contained an abundance of membranes and had diffuse poles that lacked distinct polar MT organizing centers. From these observations we conclude that the apparent individual chromosomal spindles--seen in the light microscope to form around each Xenos tetrad during "intranuclear prometaphase" (Hughes-Schrader, S., 1924, J. Morphol. 39:157-197)--actually form during late prophase, lack MTs, and are therefore not complete miniature bipolar spindles, as had been commonly assumed. Thus, the unique mode of spindle formation in Xenos oocytes cannot be used to support the hypothesis that chromosomes (kinetochores) induce the polymerization of their associated MTs. Our observation that MTs appeared in association with and parallel to tubular membrane components of the Xenos meiotic apparatus after these membranes became oriented with respect to the tetrads, is consistent with the notion that membranes associated with the spindle determine the orientation of spindle MTs and also play a part in regulating their formation.

Animals↗

PubMed1995

Kinetics of plasma membrane and mitochondrial alterations in cells undergoing apoptosis.

Programmed cell death or apoptosis is characterized by typical morphological alterations. By transmission electron microscopy, apoptotic cells are identified by condensation of the chromatin in tight apposition to the nuclear envelope, alteration of the nuclear envelope and fragmentation of the nucleus, whereas integrity of the plasma membrane and organelles is preserved. Conversely cells undergoing necrosis display an early desintegration of cytoplasmic membrane and swelling of mitochondria. In this study we assessed by flow cytometry the sequential alterations of forward angle light scatter, 90 degrees light scatter, and fluorescence associated with fluorescein diacetate, rhodamine 123, and propidium iodide in two human B cell lines undergoing apoptosis induced by the topoisomerase II inhibitor VP-16. The kinetics of these modifications were compared to those of cells undergoing necrosis induced by sodium azide. At the same time intervals, cells were examined by transmission electron microscopy and by UV microscopy after staining with Hoechst 33342. We report that sequential changes in light scatters and fluorescein diacetate are similar in cells undergoing apoptosis or necrosis, whereas apoptosis is characterized by a slightly delayed decrease of mitochondrial activity as assessed by rhodamine 123 staining. Surprisingly a part of cells undergoing apoptosis displayed an early uptake of propidium iodide followed by a condensation and then a fragmentation of their nuclei. It is concluded that uptake of propidium iodide is a very early marker of cell death which does not discriminate between necrosis and apoptosis. Along with biochemical criteria, nuclear morphology revealed by staining with Hoechst 33342 would seem to be of the most simple and most discriminative assay of apoptosis.

Animals↗

PubMed1992

Deletion of the regulatory domain of protein kinase C alpha exposes regions in the hinge and catalytic domains that mediate nuclear targeting.

Members of the protein kinase C (PKC) family are characterized by an NH2-terminal regulatory domain containing binding sites for calcium, phosphatidylserine, and diacylglycerol (or tumor-promoting phorbol esters), a small central hinge region and a COOH-terminal catalytic domain. We have constructed fusion proteins in which the regulatory domain of PKC alpha was removed and replaced by a 19-amino acid leader sequence containing a myristoylation consensus or by the same sequence in which the amino-terminal glycine was changed to alanine to prevent myristoylation. The goal was to generate constitutively active mutants of PKC that were either membrane bound, due to their myristoylation, or cytoplasmic. Western blotting of fractions from COS cells transfected with plasmids encoding wild-type and mutant proteins revealed that PKC alpha resided entirely in a Triton X-100 soluble (TS) fraction, whereas both the myristoylated and nonmyristoylated mutants were associated primarily with the nuclear envelope fraction. A similar mutant that lacked the 19 amino acid leader sequence was also found almost entirely in the nuclear envelope, as was a truncation mutant containing only the regulatory domain, hinge region, and a small portion of the catalytic domain. However, an additional truncation mutant consisting of only the regulatory domain plus the first one-third of the hinge region was almost entirely in the TS fraction. A nonmyristoylated fusion protein containing only the catalytic domain was also found in the nuclear envelope. Immunostaining of cells transfected with these constructs revealed that both the myristoylated and nonmyristoylated mutants were localized in nuclei, whereas wild-type PKC alpha was primarily cytoplasmic and perinuclear. Phorbol dibutyrate treatment of PKC alpha-transfected cells resulted in increased perinuclear and nuclear staining. The results are consistent with a model in which activation of PKC, by phorbol esters or by deletion of the regulatory domain, exposes regions in the hinge and catalytic domains that interact with a PKC "receptor" present in the nuclear envelope, and may explain the ability of wild-type PKC to be translocated to the nucleus under certain conditions.

Animals↗

PubMed1988

Microtubule rearrangements during mitosis in multinucleate cells.

The peroxidase-antiperoxidase (PAP) method for the detection of polymerized tubulin has been used to study the microtubule rearrangements during mitosis in PtK1 and HeLa multinucleate cells obtained by polyethyleneglycol (PEG)-mediated fusion. We demonstrate here that the transition of the microtubular cytoskeleton from interphase to mitosis is an inducible event and independent of the factor(s) responsible for chromatin condensation and nuclear envelope breakdown. However, for the induction of the microtubule rearrangements nuclear envelope breakdown is required. At midprophase, cytoskeletal microtubule rearrangements start for multinucleate PtK1 cells, whereas in HeLa cells such changes are delayed, and a more abrupt transition is observed here. After complete nuclear envelope breakdown (prometaphase) mitotic asters and spindles but no cytoplasmic (interphase) microtubuli can be observed in both systems. Metaphase is characterized by an interaction between the different mitotic poles which show the form of bipolar spindles, but individual separated mitotic poles far removed from the chromatin can also be seen.

Animals↗

PubMed2000

Cytochemical and ultrastructural examination of apoptotic odontoclasts induced by bisphosphonate administration.

Since odontoclasts share similar characteristics with osteoclasts, this study has examined whether odontoclasts exhibit cytological alteration after treatment with bisphosphonate, which induces apoptosis of osteoclasts. After the administration of bisphosphonate to 6-day-old rabbits, many odontoclasts detached from the dentine surface of the deciduous teeth, resulting in the reduction of tartrate-resistant acid phosphatase (TRAP-ase) and immunoreactivity for cathepsin K. Transmission electron microscopy revealed a number of odontoclasts showing poorly developed or a lack of ruffled borders, a Golgi apparatus markedly reduced in size, and numerous cytoplasmic vesicles. The bisphosphonate-treated odontoclasts displayed fragmented DNA in the pyknotic nuclei evidenced by terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick-end labeling, indicating that bisphosphonate can induce apoptosis of the odontoclasts. Ultrastructural observations of the apoptotic odontoclasts revealed condensed heterochromatin at the margin of the nuclear envelope, assembled arrays of rough endoplasmic reticulum, and many vacuoles and vesicles. Some apoptotic odontoclasts showed ladder-like structures between the adjacent nuclear envelopes, enlargement of the nuclear envelopes, and the formation of a ribosome-like granular structure in the nuclei. Thus, odontoclasts are able to undergo apoptosis after bisphosphonate treatment; this results in cytological alterations, including reduced resorption activity and the inhibition of protein synthesis/transport as indicated by the diminished TRAPase and cathepsin K and the poorly developed Golgi apparatus, respectively. Nuclear alteration as evidenced by the appearance of ladder-like and ribosome-like structures was characteristic of apoptotic odontoclasts.

Acid Phosphatase↗

PubMed1996

Effect of protease inhibitors on early events of apoptosis.

Proteolysis is an early event of apoptosis which appears to be associated with activation of the endonuclease which is responsible for internucleosomal DNA cleavage. The present study was designed to reveal the possible role of proteolysis in other early events, such as chromatin condensation, nuclear breakdown, and destabilization of in situ DNA double-stranded structure. Apoptosis of human leukemic HL-60 cells and rat thymocytes was induced by different agents, including DNA topoisomerase inhibitors, an RNA antimetabolite, and the glucocorticosteroid, prednisolone. DNA degradation was evaluated by pulsed field and conventional gel electrophoresis and by the presence of in situ DNA strand breaks. DNA stability was estimated by the measure of its sensitivity in situ to denaturation. Chromatin condensation, nuclear breakdown, and other morphological changes were monitored by interference contrast and UV microscopy following cell staining with the DNA-specific fluorochrome 4',6-diamidino-2- phenylindole. Several irreversible or reversible serine protease inhibitors prevented internucleosomal DNA degradation, nuclear breakdown, and destabilization of DNA double-stranded structure. The effective inhibitors, however, did not prevent the onset of chromatin condensation, nor the loss of the fine structural framework, nor the initial step of DNA cleavage generating DNA fragments of >=50 kb in size. The data indicate that in both cell systems the activity of proteases sensitive to the inhibitors tested is needed for internucleosomal DNA cleavage to occur. The data also suggest that these proteases may be involved in dissolution of the nuclear envelope. Because nuclear matrix proteins and histones stabilize DNA in situ, and the decrease in DNA stability which occurs during apoptosis is precluded by the inhibitors, it is likely that serine proteases may degrade DNA stabilizing proteins. The activity of these proteases, however, appears needed neither for DNA cleavage to >=50-kb fragments nor for the onset of chromatin condensation which is associated with dissolution of the structural framework of the nucleus.

Animals↗

PubMed1988

Paired helical filaments and the cytoplasmic-nuclear interface in Alzheimer's disease.

The cytoplasmic-nuclear interface has been investigated by conventional thin sectioning electron microscopy of neurons from frontal lobe biopsies of 13 patients with Alzheimer's disease. Nine patients were in the early and intermediate stages of the disease and four patients in the advanced stage. Fascicles of paired helical filament-like strands and paired helical filaments appose the nuclear envelope, the nuclear pore complexes and the perinuclear polysomes. Paired helical filament profiles have also been identified in the nucleoplasm. These observations indicate that the cytoplasmic-nuclear interface and, consequently, the relationships between the cytoplasm and the nucleus, might be impaired in Alzheimer's disease.

Alzheimer Disease↗

PubMed2001

Inner nuclear membrane proteins: functions and targeting.

We summarize the properties of integral membrane proteins that reside in the inner nuclear membrane, including lamin B receptor (LBR), lamina-associated polypeptide (LAP) 1, LAP2, emerin, MAN1 and nurim. Most of these proteins interact with lamins and chromatin. Some data also suggest more speculative functions such as gene regulation and possibly sterol metabolism. Mutations in emerin and nuclear lamins have been associated with muscular dystrophies and lipodystrophy, raising new questions about the functions of inner nuclear membrane proteins. Integral proteins of the inner nuclear membrane are synthesized on the rough endoplasmic reticulum (ER) and reach the inner nuclear membrane by lateral diffusion in the connected ER and nuclear envelope membranes. Associations with nuclear ligands retain them in the inner nuclear membrane. Further investigation of the functions and targeting of inner nuclear membrane proteins are needed to determine how they are involved in human disease.

Animals↗