Gene-gene coordination by the nuclear envelope.
The paper studies how certain topologic features of the nuclear envelope may reorganize entrained transcription via spatial rearrangements of genes carried by distinct chromatids.
Animals↗
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Dilated cisternae of nuclear envelope and rough endoplasmic reticulum in the proventriculus of Drosophila auraria larvae.
In the cells of the middle layer of the proventriculus of Drosophila auraria larvae, the nuclear envelope and the rough endoplasmic reticulum are always found in the form of dilated cisternae. The length of these cisternae can reach 10 mu. There are indications that materials from the outer membrane of the nuclear envelope are directly transported to the Golgi complex of the examined cells.
Animals↗
A mutation in the RCC1-related protein pim1 results in nuclear envelope fragmentation in fission yeast.
Members of the RCC1 protein family are chromatin-associated guanine nucleotide exchange factors that have been implicated in diverse cellular processes in various organisms, yet no consensus has been reached as to their primary biological role. The fission yeast Schizosaccharomyces pombe, a single-celled eukaryote, provides an in vivo system in which to study the RCC1/Ran switch by using a temperature-sensitive mutant in the RCC1-related protein pim1. Mitotic entry in the pim1-d1ts mutant is normal, but mitotic exit leads to the accumulation of cells arrested with a medial septum and condensed chromosomes. Although the yeast nuclear envelope normally remains intact throughout the cell cycle, we found a striking fragmentation of the nuclear envelope in the pim1-d1ts mutant following mitosis. This resulted in chromatin that was no longer compartmentalized and an accumulation of pore-containing membranes in the cytoplasm. The development of this terminal phenotype was dependent on the passage of cells through mitosis and was coincident with the loss of viability. We propose that pim1 is required for the reestablishment of nuclear structure following mitosis in fission yeast.
Chromatin↗
The redistribution of a conserved nuclear envelope protein during the cell cycle suggests a pathway for chromosome condensation.
We describe a human autoantiserum that recognizes specific determinants present both on the nuclear envelope of interphase cells and the periphery of metaphase chromosomes. These determinants are highly conserved through evolution and present on a protein with an apparent molecular weight of 33,000. This 33 kd protein, which we call "perichromin," appears to be directly or indirectly bound to both interphase and metaphase DNA. Studies of the transformation of perichromin from a nuclear envelope association to a perichromosomal position during prophase suggests a pathway for chromosome organization throughout the cell cycle.
Animals↗
Annulate lamellae: comparison of antigenic epitopes of annulate lamellae membranes with the nuclear envelope.
Annulate lamellae (AL) are a membranous structure frequently observed in differentiating gametes and tumor cells. In spite of numerous morphological studies, the function and biochemical composition of this membrane system are not well understood. In this study, we have examined the AL membrane system of vinblastine-treated mouse L cells using immunocytochemistry and Western blot analysis. Our results show that antibodies directed against nuclear envelope lamins, i.e., lamins A, B, and C, did not cross react with constituents of the AL membrane system. Furthermore an AL-specific antibody failed to react with the nuclear envelope and reacted minimally producing only a background stain over other cellular components. The data suggest that the AL membrane system has a distinct molecular make-up that is antigenically distinct from that of other subcellular structures.
Animals↗
The lectin binding sites on the membranes of the nuclear envelope, mitochondria and the cell surface of human lymphoblastoid cells.
The membranes of the cell surface, the endoplasmic reticulum, outer and inner mitochondrial leaflet and nuclear envelope were isolated from three human lymphoblastoid cell lines. Membrane components were separated by dodecyl sulfate polyacrylamide gel electrophoresis and the gels incubated with the radioiodinated lectins from lentil, castor bean, scarlet runner bean, gorse seed and Roman snail. After gel slicing and counting, the molecular weights of the lectin binding sites were determined. About 20 glycoproteins were identified as constituents of the plasma membrane, a similar glycoprotein distribution was observed in the endoplasmic reticulum. The outer mitochondrial membrane contained some impurities from the plasma membrane, the inner mitochondrial membrane lacked specific lectin receptors. Two prominent glycoproteins with molecular weights of 70 000 and 60 000 were identified with the castor bean lectin in the nuclear envelope.
Cell Line↗
Live fluorescence imaging reveals early recruitment of emerin, LBR, RanBP2, and Nup153 to reforming functional nuclear envelopes.
We determined the times when the nuclear membrane, nuclear pore complex (NPC) components, and nuclear import function were recovered during telophase in living HeLa cells. Simultaneous observation of fluorescently-labeled NLS-bearing proteins, lamin B receptor (LBR)-GFP, and Hoechst33342-stained chromosomes revealed that nuclear membranes reassembled around chromosomes by 5 minutes after the onset of anaphase (early telophase) whereas nuclear import function was recovered later, at 8 minutes. GFP-tagged emerin also accumulated on chromosomes 5 minutes after the onset of anaphase. Interestingly, emerin and LBR initially accumulated at distinct, separate locations, but then became uniform 8 minutes after the onset of anaphase, concurrent with the recovery of nuclear import function. We further determined the timing of NPC assembly by immunofluorescence staining of cells fixed at precise times after the onset of anaphase. Taken together, these results showed that emerin, LBR, and several NPC components (RanBP2, Nup153, p62), but not Tpr, reconstitute around chromosomes very early in telophase prior to the recovery of nuclear import activity.
Biological Transport↗
Increased expression of nuclear envelope gp210 antigen in small bile ducts in primary biliary cirrhosis.
The sustained antibody response to nuclear envelope gp210 antigen indicates a group of primary biliary cirrhosis (PBC) patients at high risk for the progression to end-stage hepatic failure. To address this issue, we immunohistochemically studied the expression of gp210 antigen in needle liver biopsy specimens from PBC patients using a monoclonal antibody specific for gp210 antigen. The specimens from autoimmune hepatitis (AIH), chronic viral hepatitis B (CHB) and C (CHC) patients served as disease controls. The expression of gp210 antigen was apparently increased on the nuclear envelope of biliary epithelial cells (BECs) of small bile ducts in almost all specimens from PBC. In contrast, the expression of gp210 antigen was negative in BECs of small bile ducts in normal liver, while relatively weak anti-gp210 immunostaining was observed in AIH, CHC and CHB. In addition, the degree of gp210 expression in BECs of small bile ducts was positively correlated to that of portal inflammation, interface hepatitis and lobular inflammation in PBC. These results indicate that the increased expression of gp210 in small bile ducts, which is probably associated with damage to BECs by inflammation, is possibly involved in autoimmune response to gp210 leading to the progression to end-stage hepatic failure in PBC.
Adult↗
DNA from Drosophila melanogaster beta-heterochromatin binds specifically to nuclear lamins in vitro and the nuclear envelope in situ.
A DNA fragment designated lambda 20p1.4 binds in vitro to polymerized Drosophila melanogaster lamin. In situ hybridization of lambda 20p1.4 to isolated polytene chromosomes revealed localization at the chromocenter and to the 49 CD region on the right arm of chromosome 2. About 120 copies of sequences homologous to lambda 20p1.4 were detected per haploid genome. Nucleotide (nt) sequence analysis demonstrates that lambda 20p1.4 is an A + T-rich, 1327-bp fragment containing four repeated units between nt 595 and 919. Results suggest that lamin interacts with a region of lambda 20p1.4 between nt 300 and 1000. Confocal immunofluorescence co-localization demonstrates that in situ, the major locus of lambda 20p1.4 hybridization, the chromocenter, is found juxtaposed to the nuclear envelope (lamina). This is the first demonstration that a DNA sequence that binds specifically to nuclear lamins in vitro, is located at or near the nuclear envelope in situ and, presumably, in vivo.
Animals↗
Microinjection studies of protein transit across the nuclear envelope of human cells.
Proteins of various molecular weights were conjugated with rhodamine and microinjected into the cytoplasm or nucleus of HeLa cells. The injected proteins were then localized within the cells at various times thereafter with fluorescence microscopy. Proteins below approx. 60 kD rapidly crossed the HeLa nuclear envelope. Some larger proteins also were able to pass into or out of the nucleus, while others were unable to do so, indicating the selective permeability of the HeLa nuclear envelope to large proteins. The nuclear protein HMG17 accumulated within the nucleus shortly after cytoplasmic microinjection.
Biological Transport↗
Comparison of the major polypeptides of the erythrocyte nuclear envelope.
The three most abundant nonhistone polypeptides (molecular weights 75,000, 71,000 and 61,000) of the avian erythrocyte nucleus have previously been isolated in the nuclear envelope fraction. They have been separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis and peptide-mapped after limited enzymatic digestion. Three enzymes -- chymotrypsin, papain and Staphylococcus aureus protease -- were used. Results obtained with each enzyme indicate strong similarities between the three nuclear envelope polypeptides. The amino acid compositions of the two most abundant polypeptides (P75 and P71) have been determined and found to be similar. Further, they readily yield large fragments upon brief alkaline hydrolysis. For both P75, and P71 the degree and the pattern of alkaline fragmentation are almost identical. A 61,000-dalton polypeptide which appears to be P61 is obtained from P75 and P71 by mild acid hydrolysis. These results establish the close chemical similarity of these predominant polypeptides in the erythrocyte nucleus and suggest that they serve related functions.
Amino Acids↗
'Blebbing' of the nuclear envelope of mouse zygotes, early embryos and hybrid cells.
In the mouse zygote and in two-cell stage embryos the inner leaflet of the nuclear envelope of pronuclei and that of blastomere and polar body II nuclei evaginate, forming multiple blebs within the perinuclear space, which contains a granular material. Blebbing exists only in oocytes activated by sperm in vivo or in vitro, or parthenogenetically by treatment with ethanol or puromycin. The germinal vesicle and an interphase nucleus formed after treatment of the oocyte at metaphase I by puromycin do not form blebs. Formation of blebs is specifically located in the cell cycle. The burst of the blebbing activity occurs during the first half of the cell cycle in one-cell embryos and in the earliest interphase period in the second cell cycle. Blebbing ceases from the beginning of the third cell cycle. The occurrence in the cytoplasm of 'double-layered' vesicles containing granular material resembling bleb contents and the disappearance of blebs from the nuclear envelope by the end of the cell cycle provide evidence that blebs represent a step in the transport of some material from the nucleus to the cytoplasm. Ethanolic phosphotungstic acid does not stain blebs, suggesting the absence of basic protein in their contents. Blebbing can be induced in somatic (thymocyte) and embryonic (blastomere of 8-cell stage embryo) nuclei following cell hybridization with activated oocytes. Their response to the oocyte cytoplasm by initiating blebbing depends on: (1) the position of the host cell in its cell cycle at the moment of hybridization, and (2) the time spent by the foreign nuclei in the host cytoplasm following cell fusion. If donor nuclei are introduced close to the time of activation, they start to produce blebs at the time corresponding to the initiation of blebbing by the female pronucleus in the first cell cycle. If foreign nuclei are introduced a few hours after activation they must be incubated in the host cytoplasm for some time before initiation of bleb formation, provided that the host pronucleus has initiated blebbing by that time. The existence of blebbing in nuclei formed only after oocyte activation, and the timing and the general occurrence of this event during the earliest cleavage stages of almost every mammalian embryo, suggest that this special nucleocytoplasmic transport plays a specific role at the beginning of development.
Animals↗
Analysis of the phospholipid of the nuclear envelope and endoplasmic reticulum of liver cells by high pressure liquid chromatography.
A method is described for the separation and analysis of phospholipids from rat-liver nuclear envelope and endoplasmic reticulum. The procedure employs a liquid environment, to which antioxidants can be added, and results in separation of NL, PE, PI, PS, and PC in 99% purity in 12 min; analytical columns and a radial compression system may be employed. The procedure results in phospholipids with a large proportion of highly unsaturated fatty acids; some differences in fatty acid distributions were found when nuclear envelope phospholipid fractions were compared with the corresponding fractions from endoplasmic reticulum.
Animals↗
[Action of x-ray irradiation on the nuclear envelope of rat liver cells].
X-irradiation of isolated nuclear envelopes (NE) has revealed their high radiosensitivity, while irradiation of isolated intact nuclei in vitro, in the doses up to 5000 r 18--20 hours after partial hepatectomy, produced no morphological changes in NE. The damaging effect of irradiation on both nuclei and mitochondria (Mt) was revealed only with a decrease in cytochrome-c-oxidase (CO) activity in parallel with an increase in the radiation dose. One hour after the whole body irradiation of rats in the beginning of S-period, the damaging effect was recorded in both NE and Mt at the doses of 50 and 150 t, and was enhanced with the increase of irradiation dose. Morphological changes were observed mostly in the outer nuclear membrane, which lost its distinct outline and disappeared from some nuclear regions. Lethal radiation doses produced a decrease in the number of pore complexes (PC) with their evident segregation from the membranes. After irradiation in a dose of 1200 r, only the residue or "ghosts" of the PCs remained. After irradiation in doses up to 400 r, the CO-activity recovered during the first hour in Mt and during first two hours in the nuclei.
Animals↗
Analysis of the hemagglutinin glycoprotein from mutants of vaccinia virus that accumulates on the nuclear envelope.
We isolated mutants whose vaccinia hemagglutinin (HA) accumulates on nuclear envelopes and the rough endoplasmic reticulum. Mutant HA must be blocked at a pre-Golgi step because it has high-mannose-type carbohydrates but no fucose. Neither N- nor O-glycosidically linked carbohydrates are involved in the transport defect of the mutant HA, because tunicamycin, an inhibitor of N-type glycosylation, has no effect, and O-type glycosylation takes place in the Golgi organelle. The unglycosylated form of the mutant HA synthesized in the presence of tunicamycin is 3000 daltons larger than the wild type. This higher molecular weight is related to the transport defect. HAs translated in vitro also show this difference, evidence that it reflects mutation in the HA structural gene. Portions of HAs that project into the cytoplasm seem to account for this weight difference. Thus the cytoplasmic tail of glycoprotein has an important function in transport out of the rough endoplasmic reticulum.
Fucose↗
Homologies in both primary and secondary structure between nuclear envelope and intermediate filament proteins.
The A, B and C lamins are the major proteins of the nuclear envelope. The complete nucleotide sequence of the coding region of the A and C lamins shows that these proteins are identical except for their carboxy termini. The most prominent structural feature of both lamins is an alpha-helical region of repeating heptads of amino acids that shows striking homology with the entire family of cytoplasmic intermediate filament proteins. These features suggest that the nuclear envelope is made up of a network of coiled-coil polymers.
Amino Acid Sequence↗
Relocation of the carboxyterminal part of CAN from the nuclear envelope to the nucleus as a result of leukemia-specific chromosome rearrangements.
Fusion genes encoding the 3' part of the can gene are implicated in two types of leukemia. The dek-can fusion gene is present in t(6;9) acute myeloid leukemia and the set-can fusion gene is present in one case of acute undifferentiated leukemia. In order to obtain leads towards the molecular basis of these diseases, we have studied the cellular localization of the DEK-CAN and SET-CAN fusion proteins and their normal counterparts. DEK-CAN and SET-CAN were localized exclusively in the nucleus, and also DEK and SET were found to be nuclear proteins. However, CAN was mainly located at the nuclear and cytoplasmic face of the nuclear envelope. This observation is in accordance with the presence of an amino acid repeat in the C-terminal part of CAN, common to the family of nucleoporins. The C-terminal part also contains a nuclear location domain as shown by deletion analysis. This domain may be important for the presence of CAN at the nucleoplasmic side of the nuclear envelope. The relocation of the carboxyterminal part of CAN due to DEK-CAN and SET-CAN may reinforce a nuclear function of the CAN protein.
Acute Disease↗
A Ca2+- and voltage-dependent cation channel in the nuclear envelope of red beet.
The patch-clamp technique was applied to study ion conductances in various configurations of the nuclear envelope of non-enzyme-treated red beet (Beta vulgaris L.) nuclei. With excised patches a non-selective cation channel was observed, that was activated by micromolar concentrations of Ca2+ on the nucleoplasmic side of the envelope. The channel activity was also voltage-dependent and the voltage threshold of channel activation changed with the nucleoplasmic Ca2+ concentration. The most prominent conductance level was 110+/-22 pS with 150 mM KCl in the bath and pipette. The channel was permeable to small cations: permeabilities relative to K+ were PK congruent with PNa=1, PCs=0.3, but PCl=0.09. Calcium ions also permeated the channel with PCa=0.43, estimated from reversal potential, or 0.14, estimated from conductance ratio. Zn2+ (1 mM) when applied to the cytoplasmic side of the envelope blocked the channel activity completely, while amiloride (2 mM) reduced the channel current by 86% from the nucleoplasmic side. The properties of the whole-nucleus current (voltage-, time- and Ca2+-dependence) paralleled those observed with excised patches. The channel may provide a Ca2+-regulated pathway for passive diffusion of cations across the nuclear envelope and thus may play an important role in Ca2+-dependent nuclear processes ranging from gene transcription to apoptosis.
Calcium Channels↗