Dissolution of the condensed chromatin structures of isolated thymocyte nuclei and the disruption of deoxyribonucleoprotein by inorganic phosphate and a phosphoprotein

Adhesive and growth properties of lectin from the ascidian Didemnum ternatanum on cultivated marine invertebrate cells

The effects of N-Acetyl-D-glucosamine-specific lectin (M(r) 27 kDa) isolated from the ascidian Didemnum ternatanum on cultivated cells of molluscs and echinoderms were studied. This lectin was found to stimulate the growth or the differentiation of cultivated marine invertebrate cells depending on the stage of embryonic development at which primary cell cultures were obtained. In addition, it has been shown to increase the attachment of cells in primary cultures of these animals. The degree of attachment is considerably increased when collagen or polylysine substrates are used. Using scanning electron microscopy we have demonstrated the stage-specific effect of this lectin on embryonic sea urchin and molluscan cells. Intensive cell spreading and an alteration of cell shape were observed only at the gastrula stage, when the switching from maternal information to embryonic genes occurred. The ascidian lectin seems to have some characteristics of both an adhesive factor and a growth factor.

Comparative study of induction of endogenous DNA degradation in rat liver nuclei and intact thymocytes

A common strongly ordered multi-step-pattern of endogenous DNA degradation was induced in rat liver nuclei and intact thymocytes, prepared in the presence of chelating agents and incubated in the presence of CaCl2 and/or MgCl2. It consisted of sequential generation of 0.3 Mbp, then 0.05 Mbp DNA fragments and finally of oligo- and mononucleosomal DNA. Oligonucleosomal DNA was generated when the genome had already been disintegrated into 0.05 Mbp DNA fragments. ZnCl2 completely inhibited advanced genome cleavage to oligo- and mononucleosomal DNA without affecting the initial generation of large DNA fragments. Therefore, the endonucleolytic activity which produce large DNA fragments is different from Ca2+/Mg2+ endonuclease. The similar pattern of DNA degradation was observed in thymocytes treated with dexamethasone and with the topoisomerase II inhibitor VM-26, the agents known to induce apoptosis. The effect of VM-26 strongly suggests the involvement of topoisomerase II in generation of large DNA fragments. Multi-level organization and regulation of the chromatin structure determine the stepwise process of genome degradation. Detachment of chromatin from the nuclear matrix attachment regions may be one of the possible mechanisms of switching off the genome function and triggering the multi-step process of endogenous chromatin degradation thus leading to cell death in terminal differentiation or stress-induced apoptosis.

Specific binding of lectins with the nucleus of the sea urchin embryo and changes in the lectin affinity of the embryonic chromatin during the course of development

(1) Embryonic cells of sea urchins were made permeable by treating them with glycerol solution for the purpose of allowing penetration of macromolecules into the cell. With the use of such permeabilized cells, several kinds of fluorescent dye-labeled lectins were introduced into the cell, and it was found that some lectins showed notable affinity with the nucleus as compared with cytoplasmic structures. (2) Isolated chromatin was incubated with several kinds of fluorescent dye-labeled lectins in vitro, and the amount of lectins bound with the chromatin was measured by fluorometry. By means of this method, the lectin-binding capacity of chromatin was estimated and compared at various stages of development. It was found that lectins could be classified into three groups according to the mode of binding with the chromatin: (a) Extent of binding increased notably at the gastrula stage (Con A and RCA-120); (b) extent of binding showed a temporary decrease at the gastrula stage (TTA); and (c) very low level of binding was maintained throughout all stages, and no particular change was observed at any stage of development (WGA, SBA, and UEA-I). (3) These facts seem to suggest that lectin-binding components are contained in sea urchin chromatin, and that drastic changes occur in these components of chromatin at the stage of gastrulation. It was proposed that the lectin-binding components such as proteoglycans and glycoproteins may play regulatory roles in embryonic chromatin at early stages of development.

The effect of ions on the structure and function of facultative heterochromatin in the mealy bug

When mealy bug testis cells are placed in an isotonic salt solution, a large mass of heterochromatic chromosomes is visible. As the ionic strength is lowered, these chromosomes decondense and can no longer be distinguished from the euchromatic chromosomes. This change is reversed by returning the cells to isotonic medium. Labeling experiments showed that this recondensation process is specific in the sense that it is the original heterochromatic chromosomes which recondense. In isotonic salt solutions, the heterochromatic chromosomes synthesize little or no RNA as compared to the euchromatic chromosomes. In hypotonic solution, cells show a general decrease in RNA synthesis, but they exhibit the same pattern of RNA synthesis as cells in isotonic solution. Therefore, it is concluded that this ion-mediated decondensation of chromosomes does not increase their capacity to synthesize RNA.

Structural alteration in isolated rat liver nuclei after removal of template restriction by polyanions

Specific polyanions release DNA template restrictions for DNA synthesis in isolated rat liver nuclei. The degree to which DNA synthesis is enhanced can be correlated with a spectrum of changes in nuclear structure Each polyanion which is effective in the release of template restriction produces a characteristic alteration in nuclear ultrastructure. Polyanions which have no effect on DNA synthesis do not appear to cause any change in nuclear organization or ultrastructure. Parallel measurements of nuclear DNA release and nuclear volume changes also indicate that template-activating polyanions cause remarkable changes in the structural organization of the treated nuclei. These results indicate that DNA template activation involves direct interactions between polyanions and nuclear constituents and suggest the possibility that naturally occurring polyanions might have a role in the control of gene activity

The distribution of the water-soluble inorganic orthophosphate ions within the cell: accumulation in the nucleus. Electron probe microanalysis

Lead acetate treatment of unfixed cells immobilizes the intracellular water-soluble, inorganic orthophosphate ions as microcrystalline lead hydroxyapatite precipitates (see reference 1). These precipitates have been analyzed with the electron microprobe. A much higher concentration of phosphorus has been found in the nucleoli of maize root tip cells fixed in lead acetate-glutaraldehyde (organic phosphorus plus inorganic orthophosphate), as compared to the nucleoli of roots fixed in glutaraldehyde alone (organic phosphorus). The concentration of the inorganic orthophosphate pool in these nucleoli is three to five times as high as the concentration of the macromolecular organic phosphate. Since nearly all of the latter is in RNA, the concentration of inorganic phosphate in the nucleolus is calculated to be roughly 0.5-0.8 M. About 30%-and up to 50%-of the total cellular inorganic phosphate is accumulated in the nucleolus since the mean concentration per cell is about 10(-2)M. In the extranucleolar part of the nucleus the mean concentration was estimated by densitometry to be roughly six times less than in the nucleolus ( 0.1 M), and appears more concentrated in the nucleoplasm than in the condensed chromatin. While there is no direct evidence for the concentration in the cytoplasm, it certainly must be much lower than the mean cellular level (i.e., < 10(-2)M) since the nucleus is about 10% of the total cell volume. The implications of this compartmentation in the intact cell are discussed in connection with (A) the availability of orthophosphate ions for the cytoplasm in those processes in which these ions affect the rate of enzymatic reactions, and (B) protein nucleic acid interactions within the nucleus and nucleolus.

Nucleolar orthophosphate ions. Electron microscope and diffraction studies

Lead acetate (3-10%, pH between 4.3 and 7.0, alone or containing 2% glutaraldehyde), when used as fixative, has been demonstrated to produce an intracellular microcrystalline precipitate of lead orthophosphate, Pb(5)(PO(4))(3)OH (lead hydroxyapatite). This confirms earlier work with the light microscope (6). In interphase cells the nucleoli are sharply delimited by the massive lead phosphate precipitate. Some diffuse precipitate is found in the nucleoplasm; it is always delimited by the nuclear membrane. Nucleolar localization of this orthophosphate pool is not a diffusion artifact; the pool is probably in a loosely bound state and is not retained by conventional fixatives. In maize root cells in advanced mitotic stages the lead phosphate crystals are seen distributed throughout the cytoplasm and also relatively concentrated on the late anaphase-early telophase chromosomes. This pool of inorganic phosphate anions may be involved in the mitotic cycle of chromatin condensation, and it may be partially responsible for the absence of mature ribosomes in the nucleolus through the chelation of divalent cations. It is evident that the siver-reducing component detected in the nucleoli of fixed cells (6) is a completely different substance.