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PubMed1988

Nuclear envelope glycoprotein with poly(A) polymerase activity of rat liver: isolation, characterization, and immunohistochemical localization.

A protein with poly(A) polymerase activity has been identified and isolated from hepatic nuclear envelopes of rats to near homogeneity. The ability of the enzyme to bind to concanavalin A-agarose and to be eluted from the column with methyl alpha-D-mannopyranoside (0.2 M) as well as the inhibitory effects of alpha-mannosidase suggested that it was a glycoprotein. Poly(A) polymerase has an absolute requirement for a divalent cation, ATP, and an oligonucleotide primer. The enzyme activity with Mn2+ was about 20-fold higher than that with Mg2+. Several known inhibitors adversely affected poly(A) polymerase activity. The enzyme has a molecular weight of 64,000 when analyzed by polyacrylamide gel electrophoresis under denaturing conditions and has a sedimentation coefficient of 4.5 S. Immunohistochemical studies using polyclonal antibodies raised against the purified enzyme revealed that the antigen was localized in the nuclear membranes.

Adenosine Triphosphate↗
PubMed1988

Nuclear envelope reformation and chromosome decondensation are dissociable events.

Cells treated with 2,4-dinitrophenol, a metabolic inhibitor, show a strong retardation of anaphase movement. At the ultrastructural level these cells reveal nuclear envelope reformation without concurrent decondensation of the chromosomes which indicates that these are possibly two dissociable late mitotic events.

2,4-Dinitrophenol↗
PubMed1987

[Systemic reorganization of the architectonics of polytene chromosomes in the onto- and phylogenesis of malarial mosquitoes. II. Species specificity in the pattern of chromosome relations with the nuclear envelope of nutrient ovarian cells].

Essential differences in the architecture of the chromosomes between the 7 species of Anopheles maculipennis complex are found. The system of chromosomes' attachment to the nuclear envelope is invariant within particular species, each of the species studied, together with homosequential A. maculipennis and A. subalpinus differing one from another. The spatial organization of nutrse ovarian cell chromosomes in experimental hybrids (A. maculipennis X A. subalpinus and A. sacharovi X A. matrinius) shows species-specificity pattern of parental species. Thus, the spatial organization of interphase nucleus is the invariant species sign, and from the author's point of view, this phenomenon is due to penetration of new type mutations--systemic mutations (according to Richard Goldschmidt), directly connected with speciation.

Animals↗
PubMed2005

The plant nuclear envelope protein MAF1 has an additional location at the Golgi and binds to a novel Golgi-associated coiled-coil protein.

Tomato MAF1 (LeMAF1) is a plant-specific, nuclear envelope (NE)-associated protein. It is the founding member of a group of WPP domain-containing, NE-associated proteins. This group includes the Arabidopsis WPP family, which is involved in cell division, as well as plant RanGAPs. In addition to its NE localization, LeMAF1 accumulates in speckles in the cytoplasm. Here, we show that the LeMAF1-containing speckles are components of the Golgi apparatus. A novel tomato coiled-coil protein was identified that specifically binds to LeMAF1. Tomato WPP domain-associated protein (LeWAP) interacts in yeast and in vitro through its coiled-coil domain with several WPP-domain containing proteins, including AtRanGAP1 and the WPP family (LeMAF, WPP1 and WPP2). Like LeMAF1, LeWAP is localized at the Golgi. Moreover, we present data showing that Arabidopsis WAP is necessary for the existence of a multi-protein complex containing WPP2.

Amino Acid Sequence↗
PubMedDate not supplied

Podophyllotoxin-induced modifications of the nuclear envelope.

In spermatids of Culex tigripes (Culicidae) the manchette is composed of numerous expansion-bearing microtubules which surround the nucleus. Under the action of podophyllotoxin, in zones where manchette microtubules are absent, the nuclear envelope bulges and forms abnormal extranuclear vesicles. We hypothesize that this newly recognized capacity of podophyllotoxin is due to its action on microtubule-membrane relationships.

Animals↗
PubMed2005

[Specific DNA sequences are associated with nuclear envelopes of pseudonurse cells in Drosophila melanogaster otu 11].

Nuclei of ovarian pseudonurse cells from the mutant strain of Drosophila melanogaster otu 11 are suitable for mapping the attachment of chromosomes to the nuclear envelope (NE). Loci in contact with the NE included region 20CD of the X chromosome, region 41 of chromosome 2, the proximal end of region 81 of chromosome 3, and region 101 of chromosome 4. In situ hybridization revealed that all 4 regions contained sequences homologous to clone lambda20p1.4. DNA of clone lambda20p1.4 was previously found to bind specifically to purified D. melanogaster lamins. These results suggest that specific DNA sequences are involved in attachment of chromosomes to NE in vivo.

Animals↗
PubMed1983

Immunoelectron microscopy of the outer membrane of rat hepatocyte nuclear envelopes in relation to the rough endoplasmic reticulum.

Prefixed nuclei were isolated from rat liver after perfusion with dilute glutaraldehyde. These nuclei sometimes were associated with the rough endoplasmic reticulum (ER), and occasionally continuity of the outer nuclear membrane with rough ER membrane was found. When these prefixed nuclei were incubated with ferritin antibody conjugates against cytochrome P-450, the cytoplasmic face of the outer nuclear membrane was labeled with ferritin similar to the labeling of the rough ER membrane. In the nuclear pore region, ferritin particles were present on the outer membrane up to the outer annuli of the pore complexes. When unfixed nuclei were incubated at 0-4 degrees C or at 20 degrees C, some outer nuclear membranes were detached from the nuclear surface. In this case the nuclear pore complexes remained associated with the inner nuclear membrane, and small inside-out vesicles were formed at these pore regions. We also found some rough vesicles heavily labeled with ferritin particles within the nuclear matrix. They probably were derived from the rough ER or from the outer nuclear envelope which was internalized artificially during incubation.

Animals↗
PubMed1994

Open states of nuclear envelope ion channels in cardiac myocytes.

Prevalent nucleocytoplasmic transport theory views flow of monoatomic ions as completely unrestricted, resulting from the presence of large diameter pore complexes (NPCs) that perforate, but hold together, the two separate membranes of the nuclear envelope (NE). However, three lines of investigations indicate that, at least in some cell types, monoatomic ion flow is restricted. (i) Patch clamp reveals quantized, ion channel-like activity in several NE preparations; activity thought to result from nuclear ion channels (NICs) connected to NPCs. (ii) Ratiometric fluorescence microscopy demonstrates that ions, as well as small molecules relevant to signal transduction, do distribute as if there is a NE barrier. (iii) Electron microscopy shows that NPCs contain material that behaves like a plug. NICs' large conductance (up to 1,000 pS) makes them a major determinant of nuclear ion concentrations which, in turn, influence nuclear processes. Therefore, NICs are an important modulating force of gene and transcriptional activities--two major determinants of gene expression. As nuclear processes may take from seconds (e.g., signaling) to minutes (e.g., transcription), the time the channels dwell in the ion-conducting open state is relevant to understanding NICs' role in nuclear function. Consequently, dwell-times and lifetimes of open NIC states were studied in 61 patch-clamped adult mouse cardiac myocyte nuclei. Upon voltage stimulation, NICs opened to main states of large conductance (281 +/- 198 pS, range = 120-490 pS, n = 55) and wide-range mean dwell-times (approximately 100 msec, 1-10 sec, and min). Closed states (0 pS) also had widely distributed mean dwell-times (approximately 100 msec, 1-10 sec, and min). Putative open substates (37 +/- 11 pS, range = 25-50, pS, n = 6) of high bursting frequency (< 1 msec) were observed without intervening main states (approximately 5% of patches). Fast (approximately 0.1 msec) and slow (approximately 10 msec) state-transitions were also detected. These observations suggest a role of NICs in mediating cytoplasmic signal control of cardiomyocyte gene expression.

Animals↗
PubMed1993

Bidirectional transport of glucocorticoid receptors across the nuclear envelope.

We have used transient interspecies heterokaryons to analyze nucleocytoplasmic shuttling of glucocorticoid receptor (GR) and demonstrated that receptors that accumulate within nuclei upon ligand binding are not statically confined to that compartment, but rather have the capacity to reversibly transverse the nuclear envelope. The ability of various GR mutants to shuttle between nuclei of heterokaryons excluded transcriptional activation and DNA binding as prerequisites for nucleocytoplasmic shuttling of GR. However, a constitutively nuclear GR derivative that has fused at its amino terminus the simian virus 40 large tumor antigen nuclear localization signal sequence was unable to efficiently export from nuclei unless ligand-bound. These results uncover an unexpected effect of ligand binding to GR--i.e., the overriding of a dominant negative effect on nuclear export of a heterologous nuclear import signal sequence. Furthermore, they demonstrate that a nuclear import signal sequence can influence nuclear processing pathways that culminate in efficient nuclear export.

3T3 Cells↗
PubMed2002

Role of delayed nuclear envelope breakdown and mitosis in Wolbachia-induced cytoplasmic incompatibility.

The bacterium Wolbachia manipulates reproduction in millions of insects worldwide; the most common effect is cytoplasmic incompatibility (CI). We found that CI resulted from delayed nuclear envelope breakdown of the male pronucleus in Nasonia vitripennis. This caused asynchrony between the male and female pronuclei and, ultimately, loss of paternal chromosomes at the first mitosis. When Wolbachia were present in the egg, synchrony was restored, which explains suppression of CI in these crosses. These results suggest that Wolbachia target cell cycle regulatory proteins. A striking consequence of CI is that it alters the normal pattern of reciprocal centrosome inheritance in Nasonia.

Animals↗
PubMed1980

Fluorescent staining of nuclear envelope coated with heparin.

Naturally and artificially devitalized cells of various origin can be loaded with heparin and subsequently stained with DAPI, a newer fluorochrome (4',6-diamidino-2-phenylindole), leading to a bright yellow fluorescence of the nuclear envelope. Depending on the cell type it is also possible to coat the outer cell membrane with heparin or other sulphated mucopolysaccharides and to achieve similar staining phenomena with DAPI.

Amidines↗
PubMed2002

Role of importin-beta in the control of nuclear envelope assembly by Ran.

Compartmentalization of the genetic material into a nucleus bounded by a nuclear envelope (NE) is the hallmark of a eukaryotic cell. The control of NE assembly is poorly understood, but in a cell-free system made from Xenopus eggs, NE assembly involves the small GTPase Ran. In this system, Sepharose beads coated with Ran induce the formation of functional NEs in the absence of chromatin. Here, we show that importin-beta, an effector of Ran involved in nucleocytoplasmic transport and mitotic spindle assembly, is required for NE assembly induced by Ran. Concentration of importin-beta on beads is sufficient to induce NE assembly in Xenopus egg extracts. The function of importin-beta in NE assembly is disrupted by a mutation that decreases affinity for nucleoporins containing FxFG repeats. By contrast, a truncated protein that cannot interact with importin-alpha is functional. Thus, importin-beta functions in NE assembly by recruiting FxFG nucleoporins rather than by interaction through importin-alpha with karyophilic proteins carrying classical nuclear localization signals. Importin-beta links NE assembly, mitotic spindle assembly, and nucleocytoplasmic transport to regulation by Ran and may coordinate these processes during cell division.

Amino Acid Motifs↗
PubMed2001

Nuclear envelope defects associated with LMNA mutations cause dilated cardiomyopathy and Emery-Dreifuss muscular dystrophy.

Nuclear lamin A and C alleles that are linked to three distinct human diseases have been expressed both in HeLa cells and in fibroblasts derived from Lmna null mice. Point mutations that cause dilated cardiomyopathy (L85R and N195K) and autosomal dominant Emery-Dreifuss muscular dystrophy (L530P) modify the assembly properties of lamins A and C and cause partial mislocalization of emerin, an inner nuclear membrane protein, in HeLa cells. At the same time, these mutant lamins interfere with the targeting and assembly of endogenous lamins and in this way may cause significant changes in the molecular organization of the nuclear periphery. By contrast, lamin A and C molecules harboring a point mutation (R482W), which gives rise to a dominant form of familial partial lipodystrophy, behave in a manner that is indistinguishable from wild-type lamins A and C, at least with respect to targeting and assembly within the nuclear lamina. Taken together, these results suggest that nuclear structural defects could contribute to the etiology of both dilated cardiomyopathy and autosomal dominant Emery-Dreifuss muscular dystrophy.

Animals↗
PubMed1996

Conserved binding recognition elements of sperm chromatin, sperm lipophilic structures and nuclear envelope precursor vesicles.

Detergent-resistant, lipophilic structures (LSs) at the apex and base of the conical sea urchin sperm nucleus are targets for cytoplasmic membrane vesicle (MV) binding and fuse with these vesicles to form a nuclear envelope in vitro. We report similar LSs associated with trout, frog and mammalian (mouse and bovine) sperm nuclei. The LSs are located at the implantation fossae of all species examined, as well as in the ventral hook region of mouse sperm nuclei. LSs can be removed from, and reconstituted back to, their original sites on nuclei. LS removal prevents MV binding, and reconstitution restores MV binding and GTP-induced fusion activities. Binding of LSs to chromatin or to MVs is mediated, at least in part, by proteins on each structure. Inter-specific LS-chromatin reconstitutions using sea urchin, fish, frog, and mammalian LSs indicate that site-specific binding is not dependent on species. All LSs also bind to MVs of sea urchin or bovine origin, but sea urchin MVs will only fuse with sea urchin LSs, and mammalian MVs only with mammalian LSs. These results demonstrate the conservation between echinoderms, fish, amphibians, and mammals of recognition elements for LS-chromatin and LS-MV binding. The mechanism for fusion of LSs with cytoplasmic MVs, however, is apparently not conserved, and close apposition of MVs on the chromatin surface mediated by LSs is not sufficient to permit MV-MV fusion in the presence of GTP.

Animals↗
PubMed1995

Nuclear-envelope nucleoside triphosphatase kinetics and mRNA transport following brain ischemia and reperfusion.

STUDY HYPOTHESIS: We attempted to determine whether the reduced egress of mRNA from brain nuclei following in vivo ischemia and reperfusion is caused by direct damage to the nuclear pore-associated NTPase that impairs the system for nuclear export of polyadenylated, or poly(A)+, mRNA. DESIGN: Prospective animal study. INTERVENTIONS: NTPase activity and poly(A)+ mRNA transport were studied in nuclear envelope vesicles (NEVs) prepared from canine parietal cortex isolated after 20 minutes of ischemia or 20 minutes of ischemia and 2 or 6 hours of reperfusion. RESULTS: Brain NEV NTPase Michaelis-Menten constant (Km) and maximum uptake velocity (Vmax) and the ATP-stimulated poly(A)+ mRNA egress rates were not significantly affected by ischemia and reperfusion. In vitro exposure of the NEVs to the OH. radical-generating system completely abolished NTPase activity. CONCLUSION: We conclude that brain ischemia and reperfusion do not induce direct inhibition of nucleocytoplasmic transport of poly(A)+ mRNA. This suggests that the nuclear membrane is not exposed to significant concentrations of OH. radical during reperfusion.

Acid Anhydride Hydrolases↗
PubMed1995

Aphidicolin-sensitive DNA polymerase is incorporated into the chromatin during nuclear envelope assembly in Xenopus egg extract.

The mechanism for incorporation of aphidicolin-sensitive DNA polymerase into reconstituting sperm nuclei was studied in a Xenopus egg extract cell-free system. Aphidicolin-sensitive DNA polymerase activity was sedimented along with the light membrane fraction of Xenopus egg extract on a discontinuous sucrose gradient. Treatment of the egg extract with Triton X-100 caused DNA polymerase activity to migrate to a lighter density position at which free proteins were distributed. DNA polymerase activity was incorporated into the reconstituting sperm nuclei from the egg extract, but no nuclear incorporation was observed in nuclei incubated in egg extracts which had been treated with Triton X-100 or sonicated. The incorporation was also prohibited by several different treatments of the egg extract resulting in incomplete assembly of the nuclear membrane on the sperm nuclei. On the other hand, there was no inhibition of nuclear incorporation into the sperm nuclei reconstituting in the extracts which had been depleted of WGA-binding pore complex proteins or which contained a specific inhibitor of topoisomerase II (ICRF-193). In these two cases, the nuclear double-layered membrane assembled normally, although in the former case the sperm nuclei lacked lamina and did not initiate DNA replication, and in the latter case the sperm nuclei did not decondense but initiated DNA replication. Thus, it is concluded that DNA polymerase activity is incorporated into the reconstituting nuclei via the membraneous/particulate fraction of the egg extract simultaneously with nuclear double-layered membrane assembly. The lamina assembly and the transport system via the nuclear envelope pore complex are suggested not to participate in DNA polymerase nuclear incorporation.

Animals↗
PubMed2004

TorsinA in the nuclear envelope.

Early-onset torsion dystonia, a CNS-based movement disorder, is usually associated with a single amino acid deletion (Delta E302/303) in the protein torsinA. TorsinA is an AAA+ ATPase in the endoplasmic reticulum, but what it does is unknown. Here, we use torsinA mutants with defects in ATP hydrolysis (E171Q, ATP-bound) and ATP binding (K108A, ATP-free) to probe torsinA's normal cellular function. Surprisingly, ATP-bound torsinA is recruited to the nuclear envelope (NE) of transfected cells, where it alters connections between inner and outer nuclear membranes. In contrast, ATP-free torsinA is diffusely distributed throughout the endoplasmic reticulum and has no effect on the NE. Among AAA+ ATPases, affinity for substrates is high in the ATP-bound and low in the ATP-free state, leading us to propose that component(s) of the NE may be substrates for torsinA. We also find that the disease-promoting Delta E302/303 mutant is in the NE, and that this relocalization, as well as the mutant's previously described ability to induce membranous inclusions, is eliminated by the K108A ATP-binding mutation. These results suggest that changes in interactions involving torsinA in the NE could be important for the pathogenesis of dystonia and point to torsinA and related proteins as a class of ATPases that may operate in the NE.

Adenosine Triphosphatases↗
PubMed1961

On the fine structure and composition of the nuclear envelope.

Nuclei from nearly ripe eggs of Rana pipiens were isolated and cleaned in 0.1 M KCl. The whole nucleus was then digested to various degrees with ribonuclease or trypsin, followed by washing and fixation in either osmium tetroxide or potassium permanganate. The nuclear envelope was dissected off, placed on a grid, air dried, and compared with undigested controls in the electron microscope. Some envelopes were dehydrated, embedded in methacrylate, and sectioned. Annuli around "pores" are composed of a substance or substances, at least partially fibrillar, which is preserved by osmium but lost during permanganate fixation. Material within the "pores" is also preserved by osmium but partially lost after permanganate. No evidence of granules or tubules in the annuli was found in air dried mounts although a granular appearance could be seen in tangentially oriented thin sections. Thin sections of isolated envelopes give evidence of diffuse material within the "pores" as well as a more condensed diaphragm across their waists. In whole mounts of the envelope the total density within "pores" is relatively constant from "pore" to "pore." All material within "pores," including the condensed diaphragm, is removable by trypsin digestion. Wispy material from the "pore" structure projects into the nucleus and annular material extends into the cytoplasm. Both annular and diaphragm materials remain with the envelope when it is isolated and are thus considered a part of its structure, not merely evidences of material passing through. There is no evidence of ribonuclease-removable material in any part of the "pore" complex.

Cell Nucleus↗