The morphological relationship in electron microscopy between NOR-silver proteins and intranucleolar chromatin

The relative distribution of NOR proteins and chromatin fibers in the nucleoli was visualized in human cell line. The chromatin was revealed by a Feulgen-like procedure using osmium-ammine as DNA tracer. This selective staining was combined with NOR-silver staining. We provide morphological evidence for constant overlapping of the silver deposit sites with dispersed intranucleolar chromatin fibers. Silver stained proteins were sometimes observed in contact with the chromatin fibers, suggesting that at least some of the Ag-NOR proteins might be closely connected with the dispersed nucleolar DNA.     

Relationship between the Ag-NOR proteins and ribosomal chromatin in situ during drug-induced RNA synthesis inhibition

In human TG tumor cells, the role of silver-NOR proteins was investigated by examining their relationship with the chromatin structure during inhibition of RNA synthesis by actionomycin-D treatment. This induced segregation of the nucleoli into four distinct zones and weakened the silver reaction. The fibrillar components were found to constitute the site of silver-stained proteins segregation. Feulgen-like osmium-ammine staining revealed that the DNA disappeared from the segregated nucleoli except for a network of nonnucleosomal filaments. When Ag-NOR protein detection was combined with chromatin visualization, we found constant overlapping of the silver reaction sites with the nonnucleosomal DNA filaments. Our results indicate that certain Ag-NOR proteins are not directly linked to active rRNA synthesis, but might rather affect the structure of ribosomal genes.     

Structural organization of chromatin in nucleolar organizer regions of nucleoli with a nucleolonema-like and compact ribonucleoprotein distribution

We have studied the relationship between the structural organization of intranucleolar chromatin and fibrillar nucleolar structures, fibrillar centers, and RNP fibrillar component, which are the interphase counterpart of metaphase nucleolar organizer regions (NORs), in regenerating rat hepatocytes and in a human tumor cell line (TG cells). These two cell types were characterized by a nucleolonema-like and compact nucleolar RNP distribution, respectively. We found that, in sections selectively stained for DNA, the intranucleolar chromatin composed of extended, nonnucleosomal DNA filaments formed roundish agglomerates with a spatial distribution which was superimposable on that of the fibrillar centers and the RNP fibrillar component around them and on sites of the silver reaction in samples selectively stained for Ag-NOR proteins. The agglomerates of extended nonnucleosomal DNA filaments were small and numerous in regenerating hepatocyte nucleoli, in which the RNP components had a nucleolonema-like distribution, whereas they were large and few in TG cell nucleoli, in which the RNP components showed a compact organization. Since the pattern of ribosomal RNA synthesis and processing was similar in the two cell types, a model was proposed in which the difference in size and shape of the agglomerates of extended DNA might be responsible for the different structural organization of the RNP components.     

Simultaneous high resolution localization of Ag-NOR proteins and nucleoproteins in interphasic and mitotic nuclei

Summary Silver stainable proteins of the Nucleolar Organizer Regions (Ag-NOR proteins) of human breast cancer tissues have been localized at the electron microscopical level with a new method which combines a simple and reproducible one step Ag-NOR staining method combined with an acetylation procedure. This new method allows the fine identification of nucleolar components, particularly those which are stained by silver.In order to determine the cytochemical nature of the components associated with Ag-NOR proteins, the EDTA regressive preferential staining procedure for ribonucleoproteins has been applied to sections. By this means the precise localization of the Ag-NOR proteins was studied simultaneously with that of ribonucleoprotein within interphasic nucleoli and mitotic chromosomes.In interphasic nucleoli, stainable Ag-NOR proteins were localized in fibrillar centres and part of the dense fibrillar component. No silver deposits were seen on perichromatin or interchromatin fibrils and granules.In metaphasic nuclei, Ag-NOR proteins were only found on roundish fibrillar ribonucleoprotein structures, which could correspond to secondary constrictions. No silver deposits were seen on the well defined ribonucleoprotein sheet surrounding the chromosomes.In telophasic nuclei, Ag-NOR proteins were seen on the central part of roundish ribonucleoprotein fibrillar structures integrated in decondensing chromosomes. These structures have been interpreted as the nucleolar organizer regions around which rRNA synthesis resumes.In interphasic and mitotic nuclei, Ag-NOR proteins were never found within condensed chromatin but always in association with ribonucleoprotein components.The new method proposed here appears to be a useful tool for the simultaneous study of the localization of ribonucleoprotein and Ag-NOR proteins during the cell cycle.     

Scattering of the silver-stained proteins of nucleolar organizer regions in Ishikawa cells by actinomycin D.

Scattering of the silver-stained proteins of nucleolar organizer regions (Ag-NOR proteins) was produced by actinomycin D in Ishikawa cells. Scattering of Ag-NOR proteins was found only in cells treated with actinomycin D and various other agents had no effect. Scattering was dose-dependent up to 10(-2) micrograms/ml of actinomycin D, but it was not found at higher concentrations that caused marked inhibition of total DNA and RNA synthesis. Actinomycin D (10(-2) micrograms/ml) caused the following changes: (i) nucleolar segregation and (ii) emergence of dense fibrillar bodies in the nucleoplasm. Ag-NOR proteins were observed on the fibrillar centers and surrounding fibrillar components in control nucleoli, on the fibrillar and amorphous zones in segregated nucleoli, and on the dense fibrillar bodies emerging in the nucleoplasm. The scattering of Ag-NOR proteins was due to the argyrophilic nature of the dense fibrillar bodies. Actinomycin D (10(-1) micrograms/ml) also caused similar morphological alterations in the nucleolus and nucleoplasm, but Ag-NOR proteins were observed only on nucleolar remnants.     

Ultrastructural localization of nucleic acids through several cytochemical techniques on osmium-fixed tissues: comparative evaluation of the different labelings

Several cytochemical techniques, such as sodium tungstate, acid hydrolysis phosphotungstic acid (HAPTA), ethylenediaminetetraacetic acid (EDTA), RNase-gold, and osmium-ammine, have been applied for the ultrastructural demonstration of nucleic acids on sections of tissues fixed in glutaraldehyde postfixed with osmium tetroxide and embedded in Epon. In order to obtain specific results, the sections had to be treated with sodium metaperiodate prior to performing the labeling protocol. The results for each method were identical to those obtained on nonosmicated tissues; the main difference being the enhancement in the ultrastructural preservation, which allowed for higher resolution. In addition to these techniques, and for comparative evaluations, DNA was also revealed by the DNase-gold approach on nonosmicated tissue sections. The consistency in the results, obtained over the nucleus with either EDTA or the RNase-gold complex for revealing RNA and those obtained with either osmium-ammine or DNase-gold for revealing DNA, supports the high specificity of the RNase-gold, DNase-gold, and osmium-ammine techniques. Furthermore, these results demonstrate the possibility of performing various cytochemical techniques on tissues processed for routine electron microscopy.     

A combined ultrastructural approach to the study of nuclear matrix thermal stabilization

Summary Using mouse erythroleukaemia cells and different ultrastructural techniques, the morphology was investigated of the nuclear matrix obtained after incubation at 37° C of isolated nuclei. If purified nuclei were heated for 45 min at 37° C, the final matrix exhibited well-recognizable nucleolar remnants, an inner network and a peripheral lamina. Without such incubation only the peripheral lamina was seen surrounding homogeneous, finely granular material. Similar results were obtained with both araldite-embedded and freeze-fractured nuclear matrices, although in the latter case the loose granular material was not evident. Observations of araldite-embedded, heat-treated nuclei revealed clumping of heterochromatin in small, very electron-dense masses with large interchromatin spaces. These ultrastructural aspects were even more striking in freeze-fractured nuclei. Cytochemical matrix analysis by osmium-ammine staining for nucleic acids and DNase-gold labelling for DNA localization demonstrated that also matrix residual nucleic acids, mostly RNA, are stabilized by heat exposure of isolated nuclei. The results demonstrate that the morphology of heat-stabilized nuclear matrix is not artefactually affected during the preparation for conventional electron microscopy and suggest a possible involvement of nucleic acids in the heat-induced stabilization of the nuclear matrix.     

小麦细胞核仁中DNA原位位置与rRNA基因转录位点的研究

以小麦细胞为研究材料, 应用常规电子显微镜技术和DNA细胞化学特异染色NAMA-Ur技术, 在原位水平对核仁中DNA的分布和特征进行了直观的观察。结果表明, 小麦细胞核仁中DNA位于纤维中心(Fibrillar Centers, FC)、致密纤维组分(Dense Fibrillar Component, DFC)以及两者的过渡区域, 并呈现出环绕FC排布的构型; 应用RNP优先染色(Benhard staining)技术分析了核仁中RNP的分布及其原位位置, 直观的显示了小麦细胞核仁中RNP颗粒主要集中在 FC与DFC的过渡区域及DFC和颗粒组分(Granular Component, GC)中; 并且在FC与DFC的过渡区域, 它们不太均匀也不太连续地半围绕着FC而排布; 进一步借助于RNA/DNA杂合体抗体在原位水平标记和分析了细胞核仁中活跃基因转录的精细位点, 结果表明小麦细胞核仁rRNA基因的转录位点位于FC与DFC的过渡区域及DFC中。     

Preribosomal ribonucleoprotein particles are a major component of a nucleolar matrix fraction

Biochemical and morphological studies were performed on Novikoff hepatoma ascites cell nucleolar matrix fractions prepared by deoxyribonuclease I digestion and high-molarity salt extractions essentially according to a published method [Berezney, R., & Buchholz, L. A. (1981) Exp. Cell Res. 20, 4995-5002]. The nucleolar matrix fraction was enriched in polypeptides of molecular mass of 28, 37.5, 40, 70, 72, 110 (protein C23), and 160 kDa, compared to the nuclear fraction in which polypeptides of molecular mass of 31, 33.5, 43.5, 46, 50, 56, and 59 kDa were predominant. About one-fourth of the protein, half of the RNA, and less than 4% of the DNA originally present in the nucleoli remained in the matrix fraction. Addition of single agents such as ethylenediaminetetraacetic acid, ribonuclease A, or mercaptoethanol during preparation had no significant effect on the polypeptide composition of the nucleolar matrix fraction. However, the combination of mercaptoethanol and ribonuclease A caused most of the RNA and protein to be removed, including protein C23 and the 160-kDa polypeptide, with polypeptides in the range of Mr 30 000-50 000 remaining. Electron microscopy of nucleolar matrix fractions revealed the presence of particles similar in size to the granular elements of nucleoli. However, when ribonuclease A and mercaptoethanol were included in the procedure, only amorphous material remained. Many proteins of nucleolar preribosomal RNP particles were also associated with the nucleolar matrix fraction. RNA from the nucleolar matrix fraction was enriched in sequences from 18S and 28S ribosomal RNA. These results indicate that preribosomal RNP particles are major constituents of a nucleolar matrix fraction prepared by the deoxyribonuclease I-high-molarity salt method.     

Non-nucleosomal configuration of chromatin in nucleolar organizer regions of metaphase chromosomes in situ

The structure of metaphase chromatin in a human tumor cell line, TG cells, was investigated using thin sections selectively stained for DNA with the Feulgen-like osmium-ammine reaction. The bulk of metaphase chromatin was characterized by the nucleosomal configuration. Some specimens were pretreated by silver staining for selective visualization of acidic proteins of the nucleolar organizer regions. In these specimens, the osmium-amine DNA tracer revealed that the chromatin present at the sites of silver granule localization had a completely extended configuration, and never gave rise to nucleosomal structures.     

Amplification of ribosomal genes and formation of extrachromosomal nucleoli in oocytes of starfish Henricia hayashi (Asteroidea: Echinasteridae)

DNA and RNA specific dyes, Ag-NOR staining and in situ hybridization were used for studying the nucleolar apparatus in the growing oocytes of Henricia hayashi (Asteroidea: Echinasteridae). A plasmid containing ribosomal genes of Drosophila melanogaster (Kolchinsky et al., 1980) labelled with 3H by nick-translation served as an rDNA probe. Multiple extrachromosomal nucleoli are formed by the cascade type as a result of growth and subsequent fragmentation of the chromosomal (primary) rDNA body and its derivative extrachromosomal (secondary) rDNA bodies. Ribosomal genes were shown in all nucleolar structures. Argentophilia of the primary and secondary DNA bodies appears to be due to the dense packing of the rDNA-containing material. Ag(+) NORs were detected in the extrachromosomal multiple nucleoli and NOR complexes. Amplification of rDNA is a highly probable conclusion from the existing data.     

An EM Study on the Nucleolar Residual in Meristematic Cells of Vicia faba

A special structure which originates from the nucleolus and persists during mitosis is observed in meristematic cells of Vicia faba, and is called nucleolar residual in this paper. The result of conventional staining showed that the nucleolar residual (NR) was a medium electron-dense structure that could be distinguished from chromosomes. At the end of prophase, the NR was observed in the dispersing nucleolar material, which consisted principally of granules and fibrils about 15 to 20 nm in diameter. In prometaphase, the NR, composed mainly of the similar granules and fibrils, was found attached to chromosomes. Results of Bernhard's technique for RNP (ribonucleoprotein) preferential staining indicated that the main chemical component of the NR was RNP, and sometimes bleached regions showing the same reaction as chromatin in Bernhard's staining appeared in the structure. In metaphase and anaphase some of the NRs were attached to chromosomes while others existed randomly in the cytoplasm. The NR is supposed, according to its cytochemical features and its behavi0ur during the nucleolar disintegration, to be a structure composed mainly of nucleolar matrix material or nucleolar skeleton.     

Fractionation of nucleoli from auxin-treated soybean hypocotyl into nucleolar chromatin and preribosomal particles

Nucleoli from auxin-treated tissues (Glycine max L. var Wayne or Kaoshiung No. 3) were isolated and purified by Percoll density gradient centrifugation. There was a 2.1-fold increase in RNA and a 2.8-fold increase in protein after a 24-h auxin treatment per unit nucleolar DNA. More than 150 acid-soluble protein spots were associated with the auxin-treated nucleoli on two dimensional (2-D) gel electropherograms.

Nucleoli from auxin-treated tissue were fractionated by suspension in 20 millimolar dithiothreitol at room temperature for 20 minutes into two distinct fractions referred to as the nucleolar chromatin and preribosomal particle fractions. The DNA:RNA:protein ratio of the chromatin fraction was 1:2.5:14. Most of RNA polymerase 1 activity and nucleolar DNA recovered in this fraction. The acid-soluble proteins in the chromatin were resolved into 32 protein spots on 2-D gel electropherogram. The most abundant spots were identified as histones.

The nucleolar preribosomal particle fraction had a DNA:RNA:protein ratio of 1:24:102 and contained only trace amounts of RNA polymerase 1 activity and only 10 per cent of the nucleolar DNA. Acid-soluble proteins associated with these particles were resolved into 78 protein spots; 72 of these (acid-soluble) protein spots corresponded in 2-D gel electrophoresis to 80S cytoplasmic ribosomal proteins. Some 15 protein spots found in 80S ribosomal proteins were absent in the preribosomal particles. It seems reasonable, based on these data, that the enlargement of nucleoli after auxin treatment is primarily due to the large increase in ribosomal proteins and rRNA which accumulate and assemble in the nucleoli in the form of preribosomal particles.

     

多头绒泡菌核仁及其骨架中原肌球蛋白的免疫细胞化学鉴定

分离多头绒泡菌(physarum polycephalum)细胞的核仁,先用Dnase I消化,去除核仁内的DNA;然后用025mol/L (NH4)2ＳＯ４和2mol/L NaCl相继抽提去掉大部分蛋白质,制备成核仁骨架。SDSPAGE分析结果表明,核仁骨架中含有约20种多肽,其中包括37kD左右与原肌球蛋白分子量相当的多肽。以兔抗原肌球蛋白抗体为一抗,FITC标记的羊抗兔IgG抗体为二抗的间接免疫荧光检测结果表明,核仁和核仁骨架样品都能发出明亮的荧光,而对照样品未见明亮的荧光。间接免疫斑点印迹检测结果进一步证明,在核仁骨架的蛋白质成分中存在原肌球蛋白。胶体金免疫电镜检测结果显示,标记原肌球蛋白抗体的标本上有较多的金颗粒,而对照组标本上只有极少的金颗粒。金颗粒在核仁中主要呈散在分布。