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PubMed1979

Transfer of mouse nuclear envelope specific proteins to nuclei of chick erythrocytes during reactivation in heterokaryons with mouse A9 cells.

When chick erythrocyte nuclei are introduced into the cytoplasm of mouse A9 cells by cell fusion, proteins present in a fraction of the mouse nuclear envelope begin to appear in the envelope of the chick erythrocyte. The protein uptake was examined using antisera raised in chickens against the 3 major polypeptides of the nuclear pore complex-fibrous lamina fraction from rat liver nuclei. In indirect immunofluorescence studies these antisera give a strong envelope-specific staining with various mammalian but not chicken cells. Eighteen hours after cell fusion the first murine antigens can be observed in the erythrocyte nucleus. Two days after cell fusion the vast majority of the erythrocyte nuclei in cell hybrids contain some antigen and by 3 days the fluorescence of the reactivated erythrocyte nuclei reaches a level comparable to that of the mouse A9 nuclei. The rate of appearance of fluorescence in the chick nuclei depends upon the ratio of A9 cytoplasm to chick nuclei. Antigen uptake by the erythrocyte envelope is inhibited when protein synthesis is blocked suggesting that synthesis of mouse antigen, rather than a redistribution, determines the velocity or erythrocyte envelope reactivation. The early uptake of nucleospecific protein into the reactivating chick erythrocyte may not require any alteration in the nuclear envelope.

Animals↗
PubMed1979

Luteinizing hormone-accelerated redistribution of lysosome-like organelles preceding dissolution of the nuclear envelope in rat oocytes maturing in vitro.

Maturation of the mammalian oocyte is characterized in part by dissolution of the nuclear envelope, or germinal vesicle breakdown (GVB). By fluorescence microscopy after vital uptake of acridine orange (AO), redistribution and perinuclear accumulation of organelles corresponding to lysosomes occur before GVB in rat oocytes undergoing meiotic maturation in vitro. In follicle-enclosed oocytes explanted during the preovulatory gonadotropin surge (GS) and individually cultured as such in chemically defined medium at approximately 22 degrees C, lysosomes aggregated into disperse clusters after 30 min; by 60 min, perinuclear concentration of lysosomes and their essential disappearance from the cortical ooplasm were observed. GVB occurred within 120 min. In contrast, follicle-enclosed oocytes explanted before the GS displayed a generally homogeneous distribution of lysosomes and intact GV for up to 5 h in culture. In oocytes aspirated from follicles before the GS, partially denuded of granulosa cells, and cultivated without added hormone, most lysosomes concentrated around the GV within 60 min, with GVB occurring generally by 120 min. Luteinizing hormone (LH) added in vitro to the isolated preparation at 3 or 30 x 10(-8) M sharply accelerated these events. The effects of LH, not seen with 1.5 x 10(-8) M hormone, were blocked by anti-LH IgG. Up to 60 x 10(-8) M follicle-stimulating hormone or 80 x 10(-8) M prolactin were ineffective in accelerating lysosome redistribution or GVB. After GVB, lysosomes became once again uniformly dispersed and unresponsive, even to 60 x 10(-8) M added LH, a finding consistent with tachyphylaxis of target cells by independent criteria. The present data, all statistically significant at P less than 0.05, demonstrate that mobilization of lysosomes before GVB is a specific response to factors that promote resumption of meiotic maturation of rat oocytes.

Animals↗
PubMed1977

Characterization of the nuclear envelope, pore complexes, and dense lamina of mouse liver nuclei by high resolution scanning electron microscopy.

We have used high resolution scanning electron microscopy (SEM) to study the nuclear envelope components of isolated mouse liver nuclei. The surfaces of intact nuclei are covered by closely packed ribosomes which are distinguishable by SEM from nuclear pore complexes. After removal of nuclear membranes with the nonionic detergent Triton X-100, the pore complexes remain attached to an underlying, peripheral nuclear lamina, as described by others. The surface of this dense lamina is composed of particulate granules, 75-150 A in diameter, which are contiguous over the entire periphery. We did not observe the pore-to-pore fibril network suggested by other investigators, but such a structure might be the framework upon which the dense lamina is formed. Morphometric analysis of pores and pore complexes shows their size, structure, and density to be similar to that of other mammalian cells. In addition, several types of pore complex-associated structures, not previously reported by other electron microscope (EM) techniques, are observed by SEM. Our studies suggest that the major role of the dense lamina is associated with the distribution, stability, and perhaps, biogenesis of nuclear pore complexes. Treatment of isolated nuclei with a combination of Triton X-100 and sodium deoxycholate removes membranes, dense lamina, and nuclear pore complexes. The resulting "chromatin nuclei" retain their integrity despite the absence of any limiting peripheral structures.

Animals↗
PubMed1978

Effects of divalent-cation chelators and chloramphenicol on the spatial relationship of the nuclear envelope to chromatin in micronuclei of Chinese hamster cells.

In the presence of the spindle poison Colcemid in the culture medium to prevent anaphase, approximately 20% of Chinese hamster metaphase cell were converted to micronucleated cells during 7 h. In the micronuclei the chromosome had become enclosed by a nuclear envelope (NE). In the light-microscope the micronuclei were of two kinds: with either visible chromatids or with decondensed chromosomes. In the electron microscope (EM) the spatial relationship of the NE to the chromatin was of two kinds only in the presence of Colcemid. In about 90% of the micronucleated cells the spatial relationship was normal, ie, the NE was immediately adjacent to the chromatin. In the remaining cells, the NE was distended so that the outer NE was separated from the inner one. In the presence of the divalent cation chelator, (ethylenedinitrilo) tetraacetic acid (EDTA) or the Ca2+-chelator [ethylenebis (oxyethylenenitrilo)] tetraacetic acid (EGTA) in addition to Colcemid, the amount of cells with micronuclei increased to 40%. The light-microscope appearance was the same as that found in the absence of the chelating agents. However, after Colcemid plus EGTA, EM revealed that only about 50% of the micronucleated cells had NE that was immediately adjacent to the chromatin and about 10% of them had distended outer NE. In the remaining 40% a third kind of spatial relationship was seen: the NE was intact but most of it was not adjacent to the chromatin. Furthermore, this type of micronucleus often contained mitochondria within the confines of NE. Thus, Ca2+ and possibly Mg2+ may regulate the rate of formation of the NE and also its ultrastructural relation to the chromatin. Mitochondrial function also appears to be involved in this relationship. In the presence of chloramphenicol (CAP), an inhibitor of mitochondrial protein synthesis, in addition to Colcemid, only about 50% of the micronucleated cells exhibited the normal relationship. The outer NE was separated from the inner NE in about 46% of the micronucleated cells and the third kind of NE-chromatin relationship was observed only in 2%. In the case of the third kind of relationship produced by CAP, inclusion of mitochondria within the micronuclei was not observed, in contrast to the finding with EGTA.

Animals↗
PubMed1978

The influence of Triton X-100 on the nuclear envelope of the isolated liver cell nuclei.

In order to obtain more precise information on an eventual presence of extra-membranous lipids in the interior of the nucleus, the effects of Triton X-100 on the lipid content and ultrastructure of isolated rat liver nuclei was investigated. Enzyme markers (a.o. glucose-6-phosphatase) were used to control impurities of the nuclear fractions biochemically along with transmission electron microscopy and qualitative and quantitative light microscopy to check the condition of the nuclei obtained. Treatment of the nuclear fraction with increasing concentrations of Triton X-100 resulted in a decrease of the phospholipid content down to 25% at a Triton X-100/protein ratio of 0.4. A further decrease to 8% was measured at a ratio of 1.5. Electron microscopy of nuclei of the latter group showed nuclei containing outer membrane fragments in 2.5% of their surfaces. The composition of lipids extracted from a nuclear fraction appeared to be markedly changed after treatment with Triton X-100 with an increase of the percentage of neutral lipids and the phospholipids diphosphatidyl-glycerol and spingomyelin. From the chemical and morphological data obtained, the conclusion was drawn that a substantial part of the lipids remaining in the isolated nuclei after treatment with Triton X-100 is localized in both membranes of the nuclear envelope. It cannot however, be excluded that a small portion would be present in the interior of the nuclei.

Animals↗
PubMed1977

Transformation by simian virus 40 induces virus-specific, related antigens in the surface membrane and nuclear envelope.

Nucleus- and mitochondrion-free membranes from hamster lymphocytes transformed by simian virus 40 (SV40), GD248 cells, cause guinea pigs to produce immune sera that reveal the presence in GD248 plasma membranes and mitochondria of two types of glycoprotein that are not detected in membranes of normal lymphocytes [Schmidt-Ullrich, R., Thompson, W. S. & Wallach, D. F. H. (1977) Proc. Natl. Acad. Sci. USA 74, 643-647]. Indirect immune fluorescence of living, SV40-transformed T19 hamster reticulum cells, Balb/c 3T3 mouse fibroblasts, and W18 VA2 human fibroblasts, using the antisera against GD248 membrane, at 4 degrees produced a distinct cell surface fluorescence; however, above 20 degrees , staining at the nuclear perimeter, the SV40 U-antigen reaction, becomes equally prominent. In SV40-transformed cells that had been fixed in cold acetone, as well as in purified GD248 nuclei, thermostable U-antigen staining is dramatic, but there is no reaction for nuclear T-antigen. Rabbit antisera against T19 cells gave immunofluorescence reactions equivalent to those obtained with the antisera against GD248 cells. Normal guinea pig or rabbit sera and cells that had not been transformed by SV40 gave no reaction. Our sera from tumor-bearing hamsters gave only nuclear T-antigen fluorescence. The results indicate the presence of related, SV40-specific antigens in the surface membranes, nuclear envelope, and possibly other intracellular organelles of SV40-transformed cells.

Antigens, Viral↗
PubMed1979

Importance of mammalian nuclear-envelope nucleoside triphosphatase in nucleo-cytoplasmic transport of ribonucleoproteins.

The nucleoside triphosphate-stimulated efflux of RNA from isolated nuclei was studied under a range of conditions, and the effects of these conditions on the process were compared with the properties of the nucleoside triphosphatase located in the pore complex. A marked similarity between the rate of efflux and the rate of nucleoside triphosphate hydrolysis was apparent, in terms of substrate specificity, sensitivity to treatment with insolubilized trypsin, kinetics and the effects of increased ionic strength and of many inhibitors. These results are taken, in view of earlier evidence, to suggest that the activity of the nucleoside triphosphatase is a prerequisite for nucleo-cytoplasmic RNA transport in vivo. There are some indications that the nuclear-envelope lipid is also involved in regulating the efflux process.

Animals↗
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↗
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↗
PubMed1978

A microtubule--nuclear envelope complex in the spermatozoid of Pteridium.

The microtubules on the outside of the nucleus of the mature spermatozoid of Pteridium form a complex with the envelope, and the perinuclear space is eliminated. These dissimilar components are held firmly together, possibly by hydrophobic bonding. The outer part of the chromatin is also attached to the inner boundary of the envelope, and pulls away when the envelope is detached.

Cell Nucleus↗