Cell Nuclear Envelope Research Articles

A rapid activation of SRC tyrosine kinase and its binding to microtubules and nuclear envelope in cells at cut edges as a cultured wound model

A rapid activation of SRC tyrosine kinase and its binding to microtubules and nuclear envelope in cells at cut edges as a cultured wound model

Molecular Characterization and Expression Patterns of a B-Type Nuclear Lamin during Sea Urchin Embryogenesis

Developmentally regulated, tissue-specific patterns of nuclear lamin expression occur during vertebrate embryogenesis, but little is known regarding lamin ontogeny during the early development of other phyla. cDNA clones encoding a lamin from the sea urchins Strongylocentrotus purpuratus and Lytechinus variegatus have been identified, and the full coding region from the former has been sequenced. The predicted amino acid sequence indicates that this echinoderm lamin is more closely related to vertebrate B-type lamins than to dipteran fly and nematode lamina—the only other invertebrate lamina sequenced to date. Monoclonal and polyclonal antibodies to sea urchin lamin demonstrate that nuclei of unfertilized eggs and embryos exhibit relatively faint immunoreactivity until the differentiation of primary mesenchymal cells, the nuclear envelopes of which become strongly and selectively labeled by anti-lamin antibodies. Northern blots reveal stage-specific fluctuations in a single 4-kb lamin message during early development and, together with immunoblotting data, suggest that the increase in mesenchymal cell nuclear envelope immunoreactivity is due to a quantitative increase in a single type of lamin. These observations demonstrate that, similar to vertebrates, cell differentiation in invertebrates can be accompanied by a change in lamin expression patterns.

Phosphorylation of lamin B at the nuclear membrane by activated protein kinase C.

Both bryostatin 1 and 4 beta-phorbol 12,13-dibutyrate (PBt2) activate Ca2+- and phospholipid-dependent protein kinase (protein kinase C) at the plasma membrane in HL-60 cells (Kraft, A. S., Baker, V. V., and May, W. S. (1987) Oncogene 1, 91-100). However, whereas PBt2 causes HL-60 cells to cease dividing and differentiate, bryostatin 1 antagonizes this effect and allows cells to continue proliferating. To test whether these divergent effects could be due to the differential activation of protein kinase C at the nuclear level, the phosphorylation of nuclear envelope polypeptides was evaluated in cells treated with either bryostatin 1 or PBt2. Bryostatin 1, either alone or in combination with PBt2, but not PBt2 alone, mediates rapid and specific phosphorylation of several nuclear envelope polypeptides. A major target for bryostatin-induced phosphorylation is the major nuclear envelope polypeptide lamin B (Mr = 67,000, pI 6.0). In vitro studies combining purified protein kinase C and HL-60 cell nuclear envelopes demonstrate that bryostatin activates protein kinase C to phosphorylate lamin B, whereas PBt2 does so only weakly, suggesting selective activation of this enzyme toward this substrate. Comparative phosphopeptide and phosphoamino acid analyses demonstrate that bryostatin induces phosphorylation of identical serine sites on lamin B both in whole cells and in vitro. Treatment of whole cells with bryostatin, but not PBt2, leads to specific translocation of activated protein kinase C to the nuclear envelope. Since phosphorylation of lamin B is known to be involved in nuclear lamina depolymerization at the time of mitosis, it is possible that bryostatin-activated protein kinase C activity is involved in this process. Finally, specific activation of protein kinase C at the nuclear membrane could explain, at least in part, the divergent effects of bryostatin 1 and PBt2 on HL-60 cell growth.

Some effects of furazolidone on the testis and plasma levels of testosterone, luteinizing hormone and prolactin in mature male turkeys.

Adult male turkeys were treated orally with furazolidone at doses of 1, 2.5, 5 or 20 mg/kg for 14 days and their plasma analysed for luteinizing hormone (LH), testosterone and prolactin (PRL) concentrations before, during and after treatment. At 20 mg/kg the drug produced a significant decrease in the plasma levels of LH and testosterone at the end of treatment, whereas at 5 mg/kg the drug had no significant effect. Prolactin concentrations were unaffected by any of the drug doses used. Intramuscular injection of luteinizing hormone releasing hormone (LHRH) at a dose of 5 micrograms/kg produced after 30 min a significant rise in plasma levels of LH, an effect that was decreased significantly by treatment with 20 mg/kg furazolidone. Incubation of normal turkey semen with graded doses of furazolidone or nitrofurazone for up to 30 min resulted in a dose- and time-dependent decrease in sperm motility. At a concentration of 20 mg/ml a complete absence of sperm motility was observed after incubation with either drug, although, on the whole, nitrofurazone seemed more potent than furazolidone as a sperm-immobilizing agent. Histological changes occurred in the 20 mg/kg group and consisted of a decrease in spermatocyte production, corrugation of sperm cell nuclear envelopes and distention of the endoplasmic reticulum of elongate spermatids. It is concluded that furazolidone depresses pituitary LH output but may, in addition, directly affect spermatogenesis and sperm motility.

Immunofluorescence microscopy of tubulin and microtubule arrays in plant cells. III. Transition between mitotic/ cytokinetic and interphase microtubule arrays

Immunofluorescence microscopy of flowering plant root cells indicates that the earliest interphase microtubules appear during cytokinesis, radiating from the former spindle poles and subsequently from the nuclear envelope. They form networks that have microtubule focal points in the cortex underlying cell faces and in the cytoplasm between the nucleus and cortex. Cortical networks are rapidly replaced by the highly aligned array normally associated with interphase. An antibody that in animal cells identifies the location of pericentriolar material, the site of microtubule initiation, is also localized around the plant cell nuclear envelope at the time that putative early interphase microtubule networks are seen.

Nuclear envelope radiating microtubules in plant cells during interphase mitosis transition

The microtubule distribution during the transition from interphase to the mitotic phase was examined at ultrastructural level in large highly vacuolated cells ofNautilocalyx lynchii and in small non-vacuolated cells ofPisum sativum. Both cell types contain, besides preprophase bands and perinuclear microtubules, also microtubules radiating from the nucleus into the transvacuolar cytoplasmic strands and cytoplasm respectively. This microtubule array appears to be nucleated by the cell's nuclear envelope (NE) or NE-surrounding cytoplasm. It is hypothesized that the microtubules radiating from the nucleusinitially play a role in the mobilization of the nucleus whilelater on a stabilized part of this array anchors the nucleus in the plane of cell division, and thus forms a cytoskeletal link between nucleus and division site. Our results are discussed in the light of previous work on cytoplasmic behaviour during interphase-mitosis transition in highly vacuolated plant cells.

Nuclear lamina assembly, synthesis and disaggregation during the cell cycle in synchronized HeLa cells.

ABSTRACT The pattern of assembly, synthesis and disaggregation of the nuclear envelope-associated lamina in synchronized HeLa cells has been examined by means of immunofluorescence microscopy of cell preparations treated with antibody to lamina polypeptide LP67 or lamin B, using the nomenclature of Gerace and Blobel. During the cell cycle the distribution of lamina polypeptide varies dramatically. Three distinct stages can be detected with respect to its location and synthesis: Lamina polypeptide is cytoplasmically distributed during cell division particularly at the time of complete nuclear envelope breakdown. At telophase it is reassembled and becomes associated with regions of the chromosome surface. This process continues into early G1, lamina polypeptide associating progressively with the outer surface of the chromosomes; simultaneously its cytoplasmic concentration is reduced. The traffic of antigen from cytoplasm to the chromosomes is highest between telophase and G1 but continues at a reduced rate during G1. Inhibition of protein synthesis during division and G1 does not inhibit G1 lamina reformation, suggesting that the G1 lamina is constructed from depolymerized cytoplasmically-stored polypeptide derived from the previous cell cycle.Lamin B is synthesized in S-phase. The protein is rapidly accumulated at the nuclear periphery during the doubling of the nuclear surface. There is very little if any cytoplasmic location of lamina polypeptide in S-phase cells. The S-phase pattern of lamina distribution persists through early and mid G2Towards the end of G2, and particularly with the onset of prophase, the nuclear membrane-bound lamina is released into the cytoplasm over approximately 30 min. (Fusion between metaphase and either G1 or S-phase cells also results in the depolymerization of lamin B within 30 min.) Lamina polypeptides appear in the cytoplasm before the nuclear envelope has disappeared, and protein synthesis in G2, is required for complete lamina disaggregation. Lamina reformation in late mitosis and the polarity of its appearance in the telophase cell can be perturbed by treatment with colcemid or low temperature so that lamina is induced to associate with metaphase and anaphase chromosomes. In the absence of spindle microtubules lamina reformation may proceed around the surface of whole chromosomes, leading to the formation of micronuclei in G1 cells. We propose that in the normal cell nuclear envelope formation at telophase is related to the terminal distribution of cytoskeleton structures such that lamina is laid down only on the outer surface of the telophase genome beginning at the telomeric chromosome ends adjacent to the remaining mitotic fibres of the cleavage furrow.

Some ultrastructural aspects of mitosis and early differentiation in human foetal lung.

In rapidly dividing human foetal lung cells there is evidence of synthesis of extra membrane prior to mitosis. During prophase the nuclear envelope breaks down and is conserved as long double or complex stacks during the following stages of mitosis. It is suggested that the membrane is retained partly for incorporation into the daughter cell nuclear envelopes and partly for the formation of RER. The relevance of the observations to the biochemical data in the literature concerning the formation of intracellular membranes is discussed briefly.

ELECTRON MICROSCOPE OBSERVATIONS OF TELOPHASE II IN THE FLORIDEOPHYCEAE1

SUMMARYTetrahedral tetrasporangia of several florideophycean red, algae were examined with the electron microscope for details of meiosis. Only telophase II nuclei are described since earlier stages were not, observed. Both divisions of meiosis are presumed to occur within the confines of the original tetrasporangial mother cell nuclear envelope. Four nuclei are then formed simultaneously. These observations essentially support Yamanouchi's description of telophase II in Polysiphonia flexicaulis (Harvey) Collins (as P. violacea) and suggest that meiosis in these algae could be basically similar to “uninuclear meiosis” in the fungi Saprolegnia and Saccharomyces.

Involvement of the host cell nuclear envelope membranes in the replication of Japanese encephalitis virus.

The distribution of viral ribonucleic acid (RNA) on various cell membrane fractions derived from a porcine kidney cell line infected with Japanese encephalitis virus was investigated. At 40 h postinfection, after virus growth had reached its peak, three viral RNAs, 45S, 27S, and 20S, were associated with the cytoplasmic membranes and intact nuclei. The amount of each RNA associated with the nucleus was two- to fivefold greater than that present with the cytoplasmic membranes. Treatment of washed infected nuclei with 1.0% Triton X-100, which removed the outer nuclear envelope membrane, also removed the viral RNA. When the nucleus was fractionated into nuclear envelope membranes and a large particle fraction which sedimented at 600 x g, nearly all of the viral RNA remained associated with the envelope membranes. The nuclear envelope membranes contained higher viral RNA polymerase activity than the cytoplasmic membranes derived from the same cells. These data suggest that major sites for Japanese encephalitis virus RNA synthesis may be localized on or in very close association with the nuclear envelope membranes.

Composition, structure and function of HeLa cell nuclear envelope. I. Structural data.

Nuclear envelope pieces were isolated from HeLa cells, and their structure was investigated by using the negative staining technique. Structural data such as for pore diameters, pore frequency and the frequency of central granules within the pores are presented. In addition, substructural details of pore complexes as revealed by the technique employed are described. The results obtained from HeLa are compared with those of nuclear envelopes similarly prepared from diverse other kinds of cells including non-tumorous cells from human source (fetal lung fibroblasts).

On the occurrence of a fibrous lamina on the inner aspect of the nuclear envelope in certain cells of vertebrates

AbstractThe fine structure of the fibrous lamina on the inner aspect of the nuclear envelope in cells of various invertebrates is reviewed, and attention is drawn to the common occurrence of a similar but thinner layer in nuclei of cells in vertebrates. Certain superficial similarities are pointed out in the relations of fibrous lamina to the nuclear pores and of the basement lamina to the endothelial capillary pores. It is suggested that in future considerations of the physiological exchange of materials between nucleoplasm and cytoplasm the properties of the fibrous lamina must be taken into account.