Nucleoprotein localization by bismuth staining

Metallobiochemistry of ultratrace levels of bismuth in the rat II. Interaction of 205+206Bi3+ with tissue, intracellular and molecular components

BACKGROUND

Knowledge on Bi metabolism in laboratory animals refers to studies at "extreme" exposures, i.e. pharmacologically relevant high-doses (mg kg^-1 b.w.) in relation to its medical use, or infinitesimal doses (pg kg^-1b.w.) concerning radiobiology protection and radiotherapeutic purposes. There are no specific studies on metabolic patterns of environmental exposure doses (ultratrace level, μg kg^-1 b.w.), becoming in this context Bi a "heavy metal fallen into oblivion". We previously reported the results of the metabolic fate of ultratrace levels of Bi in the blood of rats [1]. In reference to the same study here we report the results of the retention and tissue binding of Bi with intracellular and molecular components.

METHODS

Animals were intraperitoneally injected with 0.8 μg Bi kg^-1 b.w. as ^205+206Bi(NO)₃, alone or in combination with ⁵⁹Fe for the radiolabeling of iron proteins. The use of ^205+206Bi radiotracer allowed the determination of Bi down to pg fg^-1 in biological fluids, tissues, subcellular fractions, and biochemical components isolated by differential centrifugation, size exclusion chromatography, solvent extraction, precipitation, immunoprecipitation and dialysis.

MAIN FINDINGS

At 24 h post injection the kidney contained by far the highest Bi concentration (10 ng g^-1 wt.w.) followed by the thymus, spleen, liver, thyroid, trachea, femur, lung, adrenal gland, stomach, duodenum and pancreas (0.1 to 1.3 ng g^-1 wt.w.). Brain and testis showed smaller but consistently significant concentrations of the element (0.03 ng g^-1 wt.w). Urine was the predominant route of excretion. Intracellularly, liver, kidney, spleen, testis, and brain cytosols displayed the highest percentages (35%-58%) of Bi of homogenates. Liver and testis nuclei were the organelles with the highest Bi content (24 % and 27 %). However, when the recovered Bi of the liver was recorded as percent of total recovered Bi divided by percent of total recovered protein the lysosomes showed the highest relative specific activity than in other fractions. In the brain subcellular fractions Bi was incorporated by neuro-structures with the protein and not lipidic fraction of the myelin retaining 18 % of Bi of the total homogenate. After the liver intra-subcellular fractionation: (i) 65 % of the nuclear Bi was associated with the protein fraction of the nuclear membranes and 35 % with the bulk chromatin bound to non-histone and DNA fractions; (ii) about 50 % of the mitochondrial Bi was associated with inner and outer membranes being the other half recovered in the intramitochondrial matrix; (iii) in microsomes Bi showed a high affinity (close to 90 %) for the membranous components (rough and smooth membranes); (iv) In the liver cytosol three pools of Bi-binding proteins (molecular size > 300 kDa, 70 kDa and 10 kDa) were observed with ferritin and metallothionein-like protein identified as Bi-binding biomolecules. Three similar protein pools were also observed in the kidney cytosol. However, the amount of Bi, calculated in percent of the total cytosolic Bi, were significantly different compared to the corresponding pools of the liver cytosol.

CONCLUSIONS

At the best of our knowledge the present paper represents the first in vivo study, on the basis of an environmental toxicology approach, aiming at describing retention and binding of Bi in the rat at tissue, intracellular and molecular levels.

Relationship of nucleolus-associated bodies with the nucleolar organizer tracks in plant interphase nuclei (Pisum sativum)

Nucleolus-associated bodies (NABs) have long been noted in interphase nuclei of a wide variety of plant species. We have recently shown that these bodies consist largely of snRNPs and that they are located on the nucleolar surface in the immediate vicinity of the nucleolar organizer tracks. The present study revealed that, following exposure of roots to KCN, an agent that induces nucleolar segregation, NABs were intimately associated with intranucleolar chromatin. Although immunocytochemical tests with anti-DNA indicated that NABs contained no demonstrable amounts of DNA, our observations nevertheless add further support to the notion that these bodies are somehow related to the nucleolar chromosomes.

A new type of ribonucleoprotein constituent of the polytene nucleus of the salivary glands of Chironomus thummi and Ch. tentans

Using electron spectroscopic imaging, a new type of small granular structural constituent has been observed in the extrachromosomal zone of the polytene nucleus of the salivary gland cells of Chironomus thummi and Chironomus tentans. These granules appear isolated or in small clumps and are often seen to be connected with surrounding thin fibrils. They are stained by the EDTA procedure, which is preferential for nuclear ribonucleoprotein (RNP) constituents, and by the bismuth oxynitrate method for visualizing phosphorylated compounds. The granules are 15-23 nm in diameter and are digested by prolonged post-embedding RNAse hydrolysis. These structural elements contain the highest concentration of phosphorus in the interchromosomal space as revealed by electron energy loss spectroscopy. The small granules exhibit several morphological and cytochemical features in common with interchromatin granules, but they are not labeled with antibodies directed against extranucleolar small nuclear RNPs (snRNPs), as are interchromatin granules.

Interchromatin granules during phytohemagglutinin stimulation of human lymphocytes. A cytochemical study

We studied the formation of interchromatin granules (IGs) in phytohemagglutinin (PHA)-stimulated lymphocytes. The bismuth staining method was used for the visualization of IGs, and we also applied high-resolution autoradiography after incubating cells in the presence of 3H-leucine during different stages of lymphocyte activation. The disaggregation of chromatin and the enlargement of interchromatinic areas in stimulated lymphocytes were found to be accompanied by an increase in the number of IGs, and it was shown that IGs were formed during all of the investigated stages of lymphocyte stimulation.

Electron microscopic staining of cytoplasmic crystalloid inclusions in preimplantation mouse embryos with Ag-NOR and glutaraldehyde-bismuth methods

Cytoplasmic crystalloid inclusions in mouse preimplantation embryos are stained with both Ag-NOR and glutaraldehyde-bismuth methods, suggesting that these inclusions may contain certain phosphorylated molecules. Since the inclusions are never found in the one-cell embryos, and their precursor-like cytoplasmic bodies appear in the two-cell embryos, they may be a product synthesized under the control of the embryonic genome.

Cytochemical study on the localization of interchromatin granules during the cell division

The localization of interchromatin granules during cell division in some mammalian cells was studied applying the bismuth staining method of Brown and Locke (1978). During the metaphase and the anaphase, the interchromatin granules remain in the cytoplasm in the form of conglomerations. In the telophase they undergo disintegration. In this process, the vacuolar system seems not to be involved.

Morphogenesis and cytochemistry of the postacrosomal dense lamina during mouse spermiogenesis

During the elongation phase of spermiogenesis in the mouse, a layer of electron-dense material appears just below the posterior portion of the acrosomal zonule. Subsequently this material accumulates on the outer side of the nuclear envelope immediately subjacent to the caudal tip of the acrosomal zonule--the anlage of the future postnuclear band--as well as on the inner side of the plasma membrane vis-à-vis to this region--the anlage of the future postacrosomal dense lamina (PADL). Corresponding to further development the postacrosomal region of the nucleus becomes directly enveloped by the plasma membrane, and the PADL, situated on its inner side, grows adequately. The postnuclear band, however, staying the same size as in the preceding elongation phase, gets shifted to the caudal end of the PADL, where it closes the perinuclear space. Since the anlagen and the mature PADL and postnuclear band show the same cytochemical reactions as the dense basal plaque of the acrosomal zonule and the thin layer on the nuclear envelope vis-à-vis to it, a relationship between these structures can be assumed. Furthermore, the demonstration of ribonucleoproteins in all these structures is discussed in connection with a possible nucleolar genesis.

Bismuth staining of a nucleolar protein

A major nucleolar protein in Chinese hamster ovary cells with a molecular weight (MW) of 100 kD has been found to stain selectively with the bismuth tartrate technique of Locke & Huie [19]. After glutaraldehyde fixation and bismuth staining of electrophoretic transfers of total nucleolar proteins separated by SDS-PAGE, a single band corresponding to the 100 kD protein is revealed. When the technique is applied to whole cells, small punctate regions of the nucleoli are strongly stained. At the ultrastructural level, bismuth selectively contrasts the fibrillar centers and the adjoining cords of the dense fibrillar component. The remainder of the dense fibrillar component is not stained. It is proposed that the high phosphorylation level of the 100 kD protein is responsible for its glutaraldehyde-insensitive bismuth staining. The concentration of this protein in certain localized regions of the nucleolus suggests that it plays a metabolic rather than a structural role.

Bismuth chemistry and the glutaraldehyde insensitive staining reaction

The free metal ion, Bi3+, is the only chemical species of bismuth that stains a strongly bismuth-reactive molecule, polyarginine, in vitro. The bismuth solution specifically requires tartrate as a chelating agent for the reaction to occur between pH 7.4 and 8.0. Since Bi3+ reacts strongly with polyarginine, creatine and ATP fixed to cellulose acetate strips and DEAE-cellulose and P-cellulose, the free metal ion (Bi3+) may bind to phosphate or guanidyl groups, or both, after glutaraldehyde fixation.

The correlation between bismuth and uranyl staining and phosphorus content of intracellular structures as determined by electron spectroscopic imaging

Four groups of intracellular structures can be recognized according to bismuth and uranyl staining and phosphorus content. (1) Those which contain phosphorus and stain strongly with uranyl acetate but not with bismuth (ribosomes, heterochromatin and mature ribosomal precursor granules), presumably because of their nucleic acid content. (2) Those which contain phosphorus and stain with uranyl acetate and bismuth (interchromatin granules, immature ribosomal precursor granules and mitochondrial granules), presumably because at least some of their phosphate is available to react with bismuth. (3) Those which contain little phosphorus but which stain strongly with bismuth and weakly with uranyl acetate (Golgi complex beads), perhaps because some ligand in addition to phosphate reacts with bismuth, and (4) those which do not contain phosphorus and stain with neither uranyl acetate nor bismuth (portasomes). Uranyl staining correlates strongly with the phosphorus content of nucleic acids, proteins and inorganic deposits. Bismuth will stain some phosphorylated molecules but not all. Thus only some phosphates stain with bismuth.

High resolution microanalysis for phosphorus in Golgi complex beads of insect fat body tissue by electron spectroscopic imaging

Golgi complex beads are 10 nm particles arranged in rings on the smooth forming face of the Golgi complex that stain specifically with bismuth in arthropod cells. In vitro experiments with biological molecules spotted on to cellulose acetate strips indicated that bismuth bound to the beads through phosphate groups. We could detect a weak phosphorus signal from the beads using a new technique called electron spectroscopic imaging that is capable of very high spatial resolution (0.3-0.5 nm) and sensitivity (50 atoms of phosphorus). Detection was not obscured by tissue staining with bismuth or uranyl acetate of by using an inorganic buffer (Na cacodylate). Localization of phosphorus was greatly improved by using colour-enhanced computer pictures of the electron spectroscopic images and quantitating the images. The results indicate that the phosphorus content of the beads is large enough to account for their bismuth reactivity.

The nucleolus during epidermal development in an insect

The fifth stadium of Calpodes has two phases of epidermal cell development corresponding to preparation for intermoult and for moult syntheses. Both phases begin with a period of elevated RNA synthesis and the elaboration of a multilobed nucleolus. The apparent number of nucleoli changes from about two to eight and back to two again within the few hours of elevated RNA synthesis. The nucleolar changes are preceded by elevated titres of haemolymph ecdysteroid. During the two periods of activity, alveoli in the matrix of the nucleoli contain particles believed to be ribosomal precursors. The staining properties of these granules differ according to size in a way that suggests a developmental sequence. Mature granules are about 20 nm in diameter and do not stain with bismuth. They are found at the periphery of the nucleolus, in the nucleoplasm, at the approaches to and within the nucleopores. Perichromatin granules, believed to be m-RNA precursor packages, are up to 60 nm in diameter, do stain with bismuth and are found at the periphery of chromatin, in nucleoplasm and distorted at the approaches to the nuclear pores to fit within the central channel. During these periods of heightened activity the nuclear envelope contains microvesicles that may be free or attached to either nuclear or cytoplasmic surfaces. The structure is appropriate for the microvesicular transnuclear envelope movement of molecules such as the ecdysteroid believed to initiate the nuclear changes.

Methods in ultrastructural cytochemistry of the cell nucleus

The electron microscopical study of the cell nucleus as observed in thin sections requires the use of cytochemical methods because of the intricate pattern of the nuclear components. The in situ techniques based on electron staining and enzymatic digestion are reviewed, excluding autoradiography, cytoenzymology and immunocytochemistry. A tentative classification has been adopted according to the chemical nature of the revealed component. Thus, the staining procedures for the nucleoproteins in general, for both nucleic acids, for the proteins, and finally for the deoxyribonucleoproteins and DNA are considered separately. 1--Stains for the nucleoproteins include simple reagents such as the uranyl and lead salts which are largely used in electron microscopy but are of limited specificity. 2--A variety of methods, some of them specific, is available for the simultaneous visualization of DNA and RNA which is based on common properties: basophilia, ability to bind diaminoacridines, presence of hydroxyl groups. However, due to the recent development of specific and preferential methods for each nucleic acid, we feel that among the older methods, only rapid and simple procedures for the detection of both nucleic acids remain of interest. 3--Proteins being ubiquitous, the useful techniques must reveal subsets within the total nuclear proteins. Apart from some endogeneous enzymes, basic proteins -- practically histones -- so far represent the only group for the detection of which reliable methods exist. 4--Several techniques developed recently are available for the specific detection of DNA. In favourable cases, methods derived from the Feulgen reaction allow its visualization at a molecular level. In addition, standard procedures for the preparation of mammalian cells and tissues are described. Each staining method is at least briefly discussed, but emphasis has been placed on a small number of techniques described in detail. They comprise the EDTA regressive stain for the ribonucleoproteins, several reactions of the basic proteins and the Feulgen-like osmium ammine reaction for DNA.