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PubMed1988

Acute ultrastructural alterations induced by soman and hypoxia in rat hippocampal CA3 pyramidal neurons.

The ultrastructural alterations in CA3 pyramidal neurons induced by the irreversible organophosphorus anticholinesterase (OP anti-ChE) pinacolyl methylphosphonofluoridate (soman) and by hypoxia were examined in rat hippocampal slices. During the first 60 min of incubation in control saline, up to 70% of the CA3 pyramidal neurons from slices superfused in control saline showed dilated cisternae of the rough endoplasmic reticulum (ER) or disrupted mitochondria. Fewer cells (10%) displayed heterochromatin clumping. With longer incubations (180 min), the number of cells showing these characteristics declined. During this time, up to 25% of these cells showed indentations in the nuclear envelope. Bath application of saline solutions containing 100 nM soman elicited periodic, spontaneously occurring epileptiform events in the CA3 subfield and substantially reduced (greater than 70%) acetylcholinesterase activity in single slices. The most characteristic ultrastructural alteration observed in response to 100 nM soman (30- to 60-min exposure) was a time-dependent, irreversible increase (up to about 60%) in the number of CA3 pyramidal neurons exhibiting indentations in the nuclear envelope. A morphometric analysis revealed a reversible, soman-induced decrease in the measured nuclear area. To test the hypothesis that these soman-induced alterations were related to hypoxic conditions, the fine structure of CA3 pyramidal neurons was characterized after the control saline was bubbled with nitrogen (95% N2, 5% CO2). In contrast to the effects induced by soman, exposure to nitrogen (15-180 min) caused dilation of rough ER cisternae, created depleted areas within the perikaryon, and produced extensive clumping of heterochromatin. In addition, more CA3 pyramidal neurons showed mitochondrial alterations after exposure to nitrogen than in control or soman-containing saline. Indentations in the nuclear envelope were not observed in response to hypoxia. We concluded that the soman-induced morphological alterations seen in vitro were comparable to those observed in hippocampi from whole animals exposed to sublethal doses of soman. The observations made in this study do not support the hypothesis that the acute alterations induced by soman in the fine structure of CA3 pyramidal neurons were the consequence of hypoxia.

Acetylcholinesterase↗
PubMed1990

A nucleolar auto-antigen is part of a major chromosomal surface component.

Several nucleolar antigens are defined by human autoantibodies. These antigens can therefore be used to follow the fate of nucleolar components through mitosis when this major nuclear structure disintegrates and becomes reassembled in G1-phase. We found that fibrillarin leaves the nucleolus before complete breakdown of this structure and attaches to chromosomes before nuclear envelope breakdown. In mouse, fibrillarin attaches over the chromosomal surface except for the excluded centromeric region. The antigen is transported to the new nucleus via the chromosomes and is last seen on chromosomal surfaces facing the cytoplasm during nuclear envelope reformation. Lamin B reappears on the same chromosomal surfaces before the nucleolar antigen is removed and aggregates for new nucleolar reformation in G1-phase cells. From our observations, we postulate that the antigen acts in concert with other proteins as a nuclear envelope equivalent by forming a protective sheath around the chromosome, that it excludes larger molecules, and helps to separate the chromosomes, in addition to segregation of the ribonucleoprotein (RNP) back to the nucleus for nucleolar reconstruction. We also suggest that the selective retention of these antigens from certain areas on individual chromosomes together with specific lamin B attachment over these chromosomal surfaces allows for a nonrandom positioning of chromosomes in the nucleus.

Animals↗
PubMed2006

The nucleoporin Nup214 sequesters CRM1 at the nuclear rim and modulates NFkappaB activation in Drosophila.

CRM1-mediated protein export is an important determinant of the nuclear accumulation of many gene regulators. Here, we show that the NFkappaB transcription factor Dorsal is a substrate of CRM1 and requires the nucleoporin Nup214 for its nuclear translocation upon signaling. Nup214 bound to CRM1 directly and anchored it to the nuclear envelope. In nup214 mutants CRM1 accumulated in the nucleus and NES-protein export was enhanced. Nup214 formed complexes with Nup88 and CRM1 in vivo and Nup214 protected Nup88 from degradation at the nuclear rim. In turn, Nup88 was sufficient for targeting the complex to the nuclear pores. Overexpression experiments indicated that Nup214 alone attracts a fraction of CRM1 to the nuclear envelope but does not interfere with NES-GFP export. By contrast, overexpression of the Nup214-Nup88 complex trapped CRM1 and Dorsal to cytoplasmic foci and inhibited protein export and immune response activation. We hypothesize that variation in levels of the Nup214-Nup88 complex at the pore changes the amount of NPC-bound CRM1 and influences the relative strength and duration of NFkappaB signaling responses.

Active Transport, Cell Nucleus↗
PubMed1992

Characterization of two human monoclonal IgM antibodies that recognize nuclear lamins.

Using immunofluorescence and immunoblotting techniques, we have identified monoclonal IgM lambda from two patients that are specific for lamins A and C and lamin B, respectively. Lamins A, B, and C are peripheral membrane proteins of the nuclear envelope with structural similarities to cytoplasmic intermediate filament proteins. When studied by indirect immunofluorescence on rat tissues, the serum containing anti-lamin B IgM stained smooth and striated muscles in addition to nuclear envelopes. Lamin B antibodies affinity purified from this serum were able to label muscle cells, suggesting that lamin B shares an epitope(s) with an unidentified muscular component(s). Since in an enzyme-linked immunosorbent assay there was no reactivity with a panel of proteins which are frequent targets of "natural" antibodies, these monoclonal IgM appear to belong to the rare category of IgM that possess a restricted specificity.

Animals↗
PubMed1996

Product of the oncogene-activating gene Tpr is a phosphorylated protein of the nuclear pore complex.

We have identified a component of the human nuclear pore complex and have shown that it is the product of a gene involved in oncogenic activation. A monoclonal antibody raised against purified nuclear matrix proteins recognizes a single protein with an electrophoretic mobility of approximately 300 kDa and stains the nuclear envelope in a punctate pattern typical of nuclear pores. The antibody was used to screen lambda gt11 human cDNA libraries, and the resulting clones were sequenced and compared to sequences in the Genbank database. An exact match was found with the human tpr (for translocated promoter region) gene, a gene shown previously to be involved in the oncogenic activation of several protein kinases. Double-label immunofluorescent microscopy with the anti-Tpr antibody and an antibody to the previously characterized nuclear pore complex protein nup153 confirms that Tpr is localized to the nuclear pore complex. Tpr is located on the cytoplasmic face of the nucleus, as demonstrated by immunofluorescent staining of cells permeabilized with digitonin. Tpr is a 2,349-amino acid protein with extensive coiled-coil domains and an acidic globular C-terminus. The protein contains 10 leucine zipper motifs and numerous sites for phosphorylation by a variety of protein kinases. Immunoprecipitation of Tpr from 32P-orthophosphate-labeled cells shows that it is a phosphoprotein. Potential functions for Tpr and possible mechanisms for the transforming activity of Tpr fusion proteins are discussed.

Animals↗
PubMed1993

Fertilization and early embryonic development in the blue fox (Alopex lagopus).

A total of 15 blue fox vixens aged 1-6 years were mated, 12 once on the first day of estrus and three a second time 48 hr after the first mating, and were killed 4 hr to 8 days following mating. Ova were collected from the oviducts, evaluated by stereomicroscopy, and studied by transmission (TEM; N = 49, 12 vixens) or scanning (SEM, N = 11, three vixens) electron microscopy. At 0-3 days after ovulation, the ova had not cleaved and were at different stages of meiotic maturation. In about one-half of these ova, representing all stages of meiotic maturation, a decondensing sperm head without nuclear envelope or a small pronucleus with partial nuclear envelope was observed. No clear relationship was found between maternal meiotic stage and the stage of paternal pronucleus formation. Sperm tails were never identified in the ooplasm. Cortical granules were released after sperm penetration at early stages of meiotic maturation. Thus the block against polyspermic penetration was activated during maturation of the oocyte. The first two-cell stage appeared 4 days after ovulation (3 days after mating), the first four-cell stage the following day (day 5), and the first eight-cell stage 6 days after ovulation (5 days after mating). In a single vixen mated late (7 days postovulation) two- to four-cell stages appeared the following day (day 8). This indicates that the time required for the first cleavage division decreases with increasing interval from ovulation to mating.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Continuous network of endoplasmic reticulum in cerebellar Purkinje neurons.

Purkinje neurons in rat cerebellar slices injected with an oil drop saturated with 1,1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate [DiIC16(3) or DiI] to label the endoplasmic reticulum were observed by confocal microscopy. DiI spread throughout the cell body and dendrites and into the axon. DiI spreading is due to diffusion in a continuous bilayer and is not due to membrane trafficking because it also spreads in fixed neurons. DiI stained such features of the endoplasmic reticulum as densities at branch points, reticular networks in the cell body and dendrites, nuclear envelope, spines, and aggregates formed during anoxia nuclear envelope, spines, and aggregates formed during anoxia in low extracellular Ca2+. In cultured rat hippocampal neurons, where optical conditions provide more detail, DiI labeled a clearly delineated network of endoplasmic reticulum in the cell body. We conclude that there is a continuous compartment of endoplasmic reticulum extending from the cell body throughout the dendrites. This compartment may coordinate and integrate neuronal functions.

Animals↗
PubMed1990

Targeting of a cytosolic protein to the nuclear periphery.

The yeast nuclear envelope protein NSP1 is located at the nuclear pores and mediates its essential function via the carboxy-terminal domain. The passenger protein, cytosolic dihydrofolate reductase from mouse, was fused to the 220 residue long NSP1 carboxy-terminal domain. When expressed in yeast, this chimeric protein was tightly associated with nuclear structures and was localized at the nuclear periphery very similar to authentic NSP1. Furthermore, the DHFR-C-NSP1 fusion protein was able to complement a yeast mutant lacking a functional NSP1 gene showing that DHFR-C-NSP1 fulfils the same basic function as compared to the endogenous NSP1 protein. These data also show that the NSP1 protein is composed of separate functional moieties: a carboxy-terminal domain that is sufficient to mediate the association with the nuclear periphery and an amino-terminal and middle repetitive domain with an as yet unknown function. It is suggested that heptad repeats found in the NSP1 carboxy-terminal domain, which are similar to those found in intermediate filament proteins, are crucial for mediating the association with the nuclear pores.

Amino Acid Sequence↗
PubMed1974

Membrane differentiations in freeze-fractured mammalian sperm.

A correlated thin-sectioning and freeze-fracturing study has been made of guinea pig and rat spermatozoa. In sections, the cell membrane over the acrosome has a concanavalin A and ruthenium red reactive glycocalyx which exhibits an ordered pattern related to the lattice of crystalline domains within the plane of the membrane revealed by freeze-fracturing. The cleaved acrosomal membrane also shows a finer linear periodicity in some areas. The membrane over the equatorial segment of the guinea pig acrosome is marked by a palisade of oblique ridges not observed in the rat. The plasmalemma of the postacrosomal region is rich in membrane intercalated particles, many randomly dispersed, others clustered in rectilinear arrays. A particle-poor zone is found just anterior to the posterior ring. The fold of redundant nuclear envelope posterior to the ring has many nuclear pores in close hexagonal array. The nuclear envelope lining the implantation fossa is devoid of pores. When cleaved it has a particle-free central area surrounded by a broad zone of large, closely packed, hollow particles. The membrane of the mid-piece in the guinea pig (but not the rat) contains linear strands of 6-8-nm particles oriented circumferentially. The membrane investing the principal piece exhibits the usual randomly distributed particles but in addition, a double row of larger (9 nm) particles runs longitudinally within the membrane over outer dense fiber 1. In the corresponding position in thin sections a local thickening of the membrane is discernible. These observations form a basis for further studies on the functional correlates of these regional specializations of the sperm membrane.

Animals↗
PubMed2004

Intranuclear membrane structure formations by CaaX-containing nuclear proteins.

The nuclear lamina is a protein meshwork lining the nucleoplasmic face of the nuclear envelope. Association of lamins with the inner nuclear membrane is mediated by specific modifications in the CaaX motif at their C-termini. B-type lamins are permanently isoprenylated whereas lamin A loses its modification by a lamin A-specific processing step after incorporation into the lamina. Lamins are differentially expressed during development and tissue differentiation. Here we show that an increased synthesis of lamins B1 and B2 in amphibian oocytes induces the formation of intranuclear membrane structures that form extensive arrays of stacked cisternae. These 'lamin membrane arrays' are attached to the inner nuclear membrane but are not continuous with it. Induction of this membrane proliferation depends on CaaX-specific posttranslational modification. Moreover, in transfected HeLa cells, chimeric GFP containing a nuclear localization signal and a C-terminal CaaX motif of N-Ras induces intranuclear membrane stacks that resemble those induced by lamins and ER-like cisternae that are induced in the cytoplasm upon increased synthesis of integral ER membrane proteins. Implications for the synthesis of CaaX-containing proteins are discussed and the difference from intranuclear fibrous lamina annulate lamellae formations is emphasized.

Amino Acid Motifs↗
PubMed1986

Nuclear division in the marine dinoflagellate Oxyrrhis marina.

The nuclear division of Oxyrrhis marina is a very distinct one among the mitoses of dinoflagellates that have been studies. Using synchronized populations, we have investigated the ultrastructural changes in this nuclear division. In interphase, nuclei can be classified into two groups on the basis of the shapes of the chromosomes. Y- and U-shaped chromosomes have been observed in both types of interphase nuclei. By prophase the nucleus becomes oval, many nuclear plaques appear on the nuclear envelope, and many microtubules radiate from these nuclear plaques within the nucleus. Metaphase can be identified by the characteristic arrangement of the chromosomes; an equatorial metaphase plate is absent. As in many higher organisms, anaphase includes two stages: anaphase A and anaphase B. During anaphase A the nucleus does not apparently elongate and the chromosomes migrate towards the poles by a combination of the shortening of the chromosome-associated microtubules and the elongation of those located between daughter chromosomes. During anaphase B the nucleus elongates to about twice its former length. This elongation may result from growth of the interzonal nuclear envelope. Dividing nucleoli are associated with microtubules, which suggests that microtubules may play an active role in the division of the nucleolus. The evolution of mitosis and the phylogenetic relationships between Oxyrrhis, typical dinoflagellates and Syndinium are discussed.

Animals↗
PubMed1989

Nuclear protein transport.

The nucleus, like all organelles, is composed of a unique set of proteins. This article discusses the possible mechanisms for localization of only certain proteins to the nucleus, transport of proteins across the nuclear envelope, and retention of proteins in the nuclear interior. In addition, nuclear protein transport is compared with transport of proteins into the endoplasmic reticulum and the mitochondria.

Amino Acid Sequence↗
PubMed1975

[The ultrastructure of the rabbit oocyte at the bilaminar follicle stage].

The electron microscope study of the nucleus and organoids of the rabbit oocytes cytoplasm during growth showed nucleoluslike bodies (RNP-granules) on the lampbrushen chromosomes to reach their maximal size at the stage of bilaminar follicle. The RNP-granules differ from the nucleoli by the time of their occurrence cytochemical characteristics, and by their ultrastructural pattern. Throughout the bilaminar follicle stage four components may be seen in the oocyte nucleolus: a dense fibrillar framework around the vacuoles, islets of the granular mass loosely dispersed, and electron dense fibrillar elements filling up the numberous electrontransparant vacuoles. The nucleolus-like bodies are round in shape and have no vacuoles, consisting to two components only: distinctly outlined granules, and weakly developed fibrillar component. The nuclear envelope is seen blebbing. Separation of two nuclear membranes forms a pocket-like enlargements of the perinuclear space. The pockets are limited by small regions between the adjacent nuclear pores. The outer membrane may bulge producing lacuma and large channels in the cytoplasm, which are interconnected making a closed branched network extending inside of the cytoplasm. The nuclear envelope is suggested to be involved in formation of the endoplasmic reticulum through the blebbing process.

Animals↗
PubMed2006

[Prevalence of antinuclear envelope antibodies and their isotypes in sera positive for antinuclear antibodies].

Antinuclear antibodies detected in HEp-2 cells by indirect immunofluorescence assay display a great variety of images, including the nuclear envelope pattern. This is quite a less frequent finding. Two thousand five hundred and ninety-four sera were processed, and 37.6% of ANA were detected. The prevalence of anti-nuclear envelope antibodies (ANEA) was of 1.2%, with a high association with autoimmune liver diseases (83%) and a low association with systemic lupus erythematosus. In 21 sera of patients with ANEA, no anti-DNAn antibodies were found; but 28.6% of anti-smooth muscle antibodies and 19% of anti-mitochondrial antibodies were detected. The triple rodent tissue section proved to be a less sensitive substrate than HEp-2 for the detection of ANEA. When using conjugates against different isotypes of antibodies for the detection of ANA, 90.5% of IgG, 66.6% of IgA and 9.5% of IgM. Two patients had ANEA-IgA at high titers (> or = 1:160) without ANEA-IgG. In this work, the importance of performing complementary tests for the detection of anti-smooth muscle antibodies, anti-mitochondrial antibodies and anti-DNAn is highlighted in order to apply these tests as guidelines for the clinical diagnosis of patients with ANEA. Besides, this study expresses the need of using total anti-Ig antibodies as conjugate for IIF-HEp-2 instead of anti-lgG; until the role of IgA antibodies in these autoimmune diseases is clarified.

Animals↗
PubMed2006

Pathology and nuclear abnormalities in hearts of transgenic mice expressing M371K lamin A encoded by an LMNA mutation causing Emery-Dreifuss muscular dystrophy.

Mutations in LMNA, which encodes nuclear lamins A and C, cause a broad range of diseases, including autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD) and related disorders with a predominant cardiomyopathy. Homozygous Lmna model "knock-in" and null mice develop cardiomyopathy, whereas heterozygous mice do not. Overexpression of lamin A mutants that cause cardiomyopathy in cultured cells induces morphological abnormalities in the nuclear envelope and lamina; however, effects on tissue and organ pathology have not been determined. We used the heart-selective alpha-myosin heavy chain promoter to drive expression in transgenic mice of human wild-type and M371K lamin A, which causes EDMD. Mice expressing M371K lamin A were born at approximately 0.07 of the expected frequency and those born typically died at 2-7 weeks of age. Histological analysis showed increased eosinophilia and fragmentation of cardiomyofibrils, nuclear pyknosis and edema without fibrosis or significant inflammation, indicative of acute or subacute injury. Mice expressing human wild-type lamin A were born at only slightly less than the expected frequency and had normal life spans. Confocal immunofluorescence microscopy demonstrated abnormal nuclear envelopes with intranuclear foci of lamins in cardiac cells expressing M371K lamin A. Electron microscopy revealed extensively convoluted nuclear envelopes, intranuclear inclusions and chromatin clumps in cardiomyocyte nuclei. These results demonstrate that expression of a lamin A mutant that induces alterations in nuclear morphology can cause tissue and organ damage in mice with a normal complement of wild-type lamins.

Animals↗
PubMed2006

The capsid protein of beak and feather disease virus binds to the viral DNA and is responsible for transporting the replication-associated protein into the nucleus.

Circoviruses lack an autonomous DNA polymerase and are dependent on the replication machinery of the host cell for de novo DNA synthesis. Accordingly, the viral DNA needs to cross both the plasma membrane and the nuclear envelope before replication can occur. Here we report on the subcellular distribution of the beak and feather disease virus (BFDV) capsid protein (CP) and replication-associated protein (Rep) expressed via recombinant baculoviruses in an insect cell system and test the hypothesis that the CP is responsible for transporting the viral genome, as well as Rep, across the nuclear envelope. The intracellular localization of the BFDV CP was found to be directed by three partially overlapping bipartite nuclear localization signals (NLSs) situated between residues 16 and 56 at the N terminus of the protein. Moreover, a DNA binding region was also mapped to the N terminus of the protein and falls within the region containing the three putative NLSs. The ability of CP to bind DNA, coupled with the karyophilic nature of this protein, strongly suggests that it may be responsible for nuclear targeting of the viral genome. Interestingly, whereas Rep expressed on its own in insect cells is restricted to the cytoplasm, coexpression with CP alters the subcellular localization of Rep to the nucleus, strongly suggesting that an interaction with CP facilitates movement of Rep into the nucleus.

Active Transport, Cell Nucleus↗
PubMed2003

Barrier-to-autointegration factor plays crucial roles in cell cycle progression and nuclear organization in Drosophila.

Barrier-to-autointegration factor (BAF) is potentially a DNA-bridging protein, which directly associates with inner nuclear membrane proteins carrying LEM domains. These features point to a key role in regulation of nuclear function and organization, dependent on interactions between the nuclear envelope and chromatin. To understand the functions of BAF in vivo, Drosophila baf null mutants generated by P-element-mediated imprecise excision were analyzed. Homozygous null mutants showed a typical mitotic mutant phenotype: lethality at the larval-pupal transition with small brains and missing imaginal discs. Mitotic figures were decreased but a defined anaphase defect as reported for C. elegans RNAi experiments was not observed in these small brains, suggesting a different phase or phases of cell cycle arrest. Specific abnormalities in interphase nuclear structure were frequently found upon electron microscopic examination of baf null mutants, with partial clumping of chromatin and convolution of nuclear shape. At the light microscopic level, grossly aberrant nuclear lamina structure and B-type lamin distribution correlated well with the loss of detectable amounts of BAF protein from nuclei. Together, these data represent evidence of BAF's anticipated function in mediating interactions between the nuclear envelope and interphase chromosomes. We thus conclude that BAF plays essential roles in nuclear organization and that these BAF functions are required in both M phase and interphase of the cell cycle.

Animals↗
PubMed1991

[Interspecies differences of co-orientation of primary polytene chromosomes in ovarian nurse cells in Drosophila melanogaster, D. simulans and D. mauritiana].

Essential differences in the architecture of primary polytene chromosomes in ovarian nurse cells between Drosophila melanogaster, D. simulans and D. mauritiana were discovered. The individual chromosomes of D. melanogaster (as well as their arms) are separated significantly from each other and are attached to the nuclear envelope by the centromeric (and the XL arm--by the telomeric) sites. D. simulans has the combination of the centromeric parts of the chromosomes X, 2, 3 into the "elongated" chromocentre, and in addition, the arms of chromosomes are also separated and attached to the nuclear envelope. Unlike the rest of the chromosomes, D. mauritiana has the chromosome 3 with firm combinated arms and the large heterochromatic block in the centromere, without being attached to the nuclear envelope.

Animals↗