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PubMed1979

The grasshopper X chromosome. I. States of condensation and the nuclear envelope at G1, S and G2 of premeiotic interphase and at early meiotic prophase.

The sub-stages of spermatocyte interphase (G1, S and G2) have been identified in the grasshopper Brachystola magna using E.M. autoradiography and serial thin sectioning techniques. The X chromosome occupies a nuclear envelope bound compartment separate from an autosome compartment during G1 and S. At G2 the X compartment is resolved by coalescence of the membranes enveloping the X chromosome and autosome compartments.--At G1 and S, the compartmentalized X chromatin is laced with nuclear membrane material. This X chromatin associated membrane decreases in amount as the cell passes through G2 and enters early meiotic prophase. There are at least 2 and possibly 3 states of condensation of the heterochromatic X during premeiotic interphase and early meiotic prophase correlated with the presence or absence of membrane material associated with the chromatin.--The X chromatin replicates asynchronously with autosomal euchromatin and synchronously with autosomal heterochromatin associated with nucleoli. The X chromatin replication appears to be associated with the nuclear membrane.--The observations indicate that the nuclear membrane is involved with X chromosome condensation and may be implicated in asynchronous X chromosome replication as well.

Animals↗
PubMed2001

The role of the nuclear envelope in Emery-Dreifuss muscular dystrophy.

The X-linked form of Emery-Dreifuss muscular dystrophy (X-EDMD) is caused by absence, or greatly reduced amounts, of the inner nuclear-membrane protein, emerin. The autosomal dominant form (AD-EDMD) is caused by missense mutations in lamins A and C, two components of the nuclear lamina that interact directly with emerin. Lamin A/C mutations also cause one form of dilated cardiomyopathy (CMD1A) and one form of limb-girdle muscular dystrophy (LGMD1B), both of which have clinical features in common with EDMD, as well as a rare, unrelated form of lipodystrophy (FPLD). Evidence is now emerging that defective assembly of the nuclear lamina is a feature of all these diseases, although not necessarily the direct cause. Why only heart and skeletal muscle, and possibly connective tissue, are affected in EDMD and why expression of the disease is so extremely variable between individuals remains to be explained.

Animals↗
PubMed2005

Breaking and making of the nuclear envelope.

During mitosis, a single nucleus gives rise to two nuclei that are identical to the parent nucleus. Mitosis consists of a continuous sequence of events that must be carried out once and only once. Two such important events are the disassembly of the nuclear envelope (NE) during the first stages of mitosis, and its accurate reassembly during the last stages of mitosis. NE breakdown (NEBD) is initiated when maturation-promoting factor (MPF) enters the nucleus and starts phosphorylating nuclear pore complexes (NPCs) and nuclear lamina proteins, followed by NPC and lamina breakdown. Nuclear reassembly starts when nuclear membranes assemble onto the chromatin. This article focuses on the different models of NEBD and reassembly with emphasis on recent data.

Animals↗
PubMed1996

Human MxB protein, an interferon-alpha-inducible GTPase, contains a nuclear targeting signal and is localized in the heterochromatin region beneath the nuclear envelope.

Interferon-inducible Mx proteins belong to the family of large GTPases and are highly homologous with dynamins within their GTP-binding domain. Cytoplasmically localized human MxA protein mediates resistance to influenza and several other viruses, whereas human MxB protein has not been found to have any antiviral activity. Here we show that MxB protein is found both in the cytoplasm and in the nucleus, where it is localized in a granular pattern in the heterochromatin region beneath the nuclear envelope. Transfection experiments in COS cells of N-terminally deleted MxB constructs revealed a functional nuclear localization signal within the first 24 N-terminal amino acids. Nuclear 78-kDa and cytoplasmic 76-kDa forms of MxB protein were found in all of the cell lines studied and in human peripheral blood mononuclear cells. MxB protein proved to be a functional GTPase with activity comparable to that of MxA protein. N-terminally truncated (delta1-82) MxB protein lacking both the nuclear localization signal and a proline-rich domain had almost completely lost its GTPase activity. Analysis of peripheral blood mononuclear cells suggested that MxB protein expression is strictly regulated by interferon-alpha. This is the first documentation that human Mx protein resides in the nucleus. It also emphasizes that there are considerable differences in the localization and structure of functional domains within Mx proteins.

Amino Acid Sequence↗
PubMed2001

The fission yeast ES2 homologue, Bis1, interacts with the Ish1 stress-responsive nuclear envelope protein.

In fission yeast, nutrient starvation induces physiological, biochemical, and morphological changes that enable survival. Collectively these changes are referred to as stationary phase. We have used a green fluorescent protein random insertional mutagenesis system to isolate two novel stress-response proteins required in stationary phase. Ish1 is a nuclear envelope protein that is present throughout the cell cycle and whose expression is increased in response to stresses such as glucose and nitrogen starvation, as well as osmotic stress. Expression of Ish1 is regulated by the Spc1 MAPK pathway through the Atf1 transcription factor. Although overexpression of Ish1 is lethal, cells lacking ish1 exhibit reduced viability in stationary phase. Bis1 is a novel interacting partner of Ish1. Bis1 is the Schizosaccharomyces pombe member of the ES2 nuclear protein family found in Mus musculus, Drosophila melanogaster, Homo sapiens, and Arabidopsis thaliana. Overexpression of Bis1 results in a cell elongation phenotype, whereas bis1(-) cells exhibit a reduced viability in stationary phase similar to that seen in ish1(-) cells.

Activating Transcription Factor 1↗
PubMed1976

The nuclear envelope in the crystalline lens fiber cell.

Rabbit lenses which have been fixed, dehydrated, and dried by a critical-point drying method, can be fractured through the cytoplasm of the differentiating lens fibers, exposing the cell nuclei. The fracture, under these conditions, causes a complete separation of the two membranes of the nuclear envelope from one another, thus exposing entire membrane surfaces (those which line the perinuclear space). These surfaces are not seen in their entirety in typical freeze-fracture or freeze-etch preparations, and consequently have not been described previously. The exposed membrane surfaces which line the perinuclear space have numerous convex structures of approximately 1,000 A, and some larger more irregularly shaped structures. These appear to be fragments of the nuclear pore complexes. Differences in these structures between young fibers and those nearing completion of differentiation is suggested.

Animals↗
PubMed1988

Nucleolar and nuclear envelope proteins of the yeast Saccharomyces cerevisiae.

We have developed a fast and reliable purification protocol to obtain yeast nuclei in intact and pure form and in a reasonable yield. The purified nuclei appear homogeneous at the light and electron microscopic level, are highly enriched in the nuclear marker histone H2B and devoid of mitochondrial, vacuolar and cytosolic marker proteins. On sodium dodecyl sulfate (SDS)-polyacrylamide gels, the nuclear fraction contains unique proteins which distinguishes them from the major yeast subcellular fractions. Yeast nuclei were separated by detergent/salt extraction into soluble, insoluble and membrane fractions. Antibodies raised against subnuclear fractions lead to the identification of an integral nuclear membrane protein and a high-abundance 38-kDa protein which is located in the yeast nucleolus.

Molecular Weight↗
PubMed2004

Nesca, a novel adapter, translocates to the nuclear envelope and regulates neurotrophin-induced neurite outgrowth.

We provide the first characterization of a novel signaling adapter, Nesca, in neurotrophic signal transduction. Nesca contains a RUN domain, a WW domain, a leucine zipper, a carboxyl-terminal SH3 domain, and several proline-rich regions. Nesca is highly expressed in the brain, is serine phosphorylated, and mobilizes from the cytoplasm to the nuclear membrane in response to neurotrophin, but not epidermal growth factor, stimulation in a MEK-dependent process. Overexpression studies in PC12 cells indicate that Nesca facilitates neurotrophin-dependent neurite outgrowth at nonsaturating doses of nerve growth factor (NGF). Similarly, short interfering RNA studies significantly reduce NGF-dependent neuritogenesis in PC12 cells. Mutational analyses demonstrate that the RUN domain is an important structural determinant for the nuclear translocation of Nesca and that the nuclear redistribution of Nesca is essential to its neurite outgrowth-promoting properties. Collectively, these works provide the first functional characterization of Nesca in the context of neurotrophin signaling and suggest that Nesca serves a novel, nuclear-dependent role in neurotrophin-dependent neurite outgrowth.

Active Transport, Cell Nucleus↗
PubMed2006

In vitro reassembly of nuclear envelopes and organelles in Xenopus egg extracts.

We reconstituted bilayer nuclear membranes, multilayer membranes, and organelles from mixtures of Xenopus laevis egg extracts and demembranated Xenopus sperm nuclei. Varying proportions of the cytosolic and vesicular fractions from the eggs were used in the reconstitution mixtures. A cytosol:vesicle ratio of 10:1 promoted reassembly of the normal bilayer nuclear membrane with inserted nuclear pore complexes around the decondensed Xenopus sperm chromatin. A cytosol:vesicle ratio of 5:1 caused decondensed and dispersed sperm chromatin to be either surrounded by or divided by unusual multilayer membrane structures with inlaid pore complexes. A cytosol:vesicle ratio of 2.5:1 promoted reconstitution of mitochondria, endoplasmic reticulum networks, and Golgi apparatus. During reassembly of the endoplasmic reticulum and Golgi apparatus, vesicular fragments of the corresponding organelles fused together and changed their shape to form flattened cisternae, which were then stacked one on top of another.

Animals↗
PubMed1975

Detection by means of cell fusion of macromolecular synthesis involved in the reconstruction of the nuclear envelope in mitosis.

Using the cultured Chinese hamster cell line Don, G1 or S or a mixture of late-S/G2 cells were prepared by release from metaphase arrest. Metaphase (M) cells were also obtained by mitotic arrest of log-phase cultures with Colcemid and held in metaphase; such M cells remained untreated with any other compound and were termed standard M cells. When interphase (I) cells were fused at pH 8.0 and 37 degrees C with standard cells in the presence of Colcemid by means of UV-inactivated Sendai virus, binucleate interphase-metaphase (I-M) cells were obtained. In a given I-M cell there occurred within 30 min after fusion either prophasing of the I nucleus or formation of a nuclear envelope (NE) around the chromosomes. About 20% of early G1 cells, 35% of cells at the G1/S boundary, 50% of S cells, and 70% of late S/G2 cells could induce NE formation. If, before fusion, cycloheximide (CHE), an inhibitor of protein synthesis, was present during release from M arrest, the cells entered G1 but not S. About 20% of such early G1 cells, like the untreated early G1 cells, had the capacity to induce NE formation during subsequent fusion. If the cells were blocked in S with 5 mM thymidine (TdR), At least 80% of these cells could induce NE formation during subsequent fusion, but in the presence of both TdR and CHE only 35% could do so. It appeared, therefore, that protein synthesis in interphase was required for NE formation. Experiments with actinomycin D indicated that RNA synthesis was also necessary for acquisition of NE-inducing capacity. About 35% of G1 cells from confluent monolayers had the NE-inducing capacity, but prolonged exposure to CHE reduced their number to 8% . Removal of CHE restored the ability while the cells still remained in G1. This result indicated that continuing protein synthesis in the G1 cell was needed for NE formation subsequent to fusion. The fact that macromolecular synthesis must occur in the I cell before fusion if NE formation was to occur in the fused I-M cell lends further support to evidence adduced earlier that this phenomenon is a normal mitotic event. Prophasing of the I nucleus in I-M cells did not appear to be dependent on macromolecular synthesis in the I cell; earlier results from this laboratory showed, however, that protein synthesis in the prior G2 period of the M cell of the I-M pair was required for prophasing.

Animals↗