Showing papers on "Nucleolus published in 1980"
TL;DR: EM investigation of Ag-AS-NOR staining after short glutaraldehyde prefixation followed by Carnoy fixation maintained good ultrastructural preservation and reactive selectivity, arguing in favour of the possibility that fibrillar centers are the interphasic counterpart of chromosome NORs.
Abstract: EM investigation of Ag-AS-NOR staining after short glutaraldehyde prefixation followed by Carnoy fixation maintained good ultrastructural preservation and reactive selectivity. This enables exact localization of silver deposits both in the fibrillar centers of typical or segregated nucleoli during interphase, and in chromosome NORs during mitosis. These results argue in favour of the possibility that fibrillar centers are the interphasic counterpart of chromosome NORs. Special structures such as nucleolar blobs and remnants usually considered to be of nucleolar origin, were also stained. — These findings seem to indicate a relationship between the distribution of the silver-stained proteins, the arrangement of the nucleolar structures and the degree of nucleolar activity resulting from the experimental conditions. These results are of interest at the time when the concept of the nucleolar matrix is gradually emerging.
146 citations
TL;DR: It is concluded that an abundance of protein-bound sulfhydryl and disulfide groups occur at nucleolar organizing regions with active genes, suggestive of a great flexibility of protein(s) by transition of sulfHydryl groups to disulfides bridges and vice versa at these highly active regions of the genome.
Abstract: Silver stainability of the chromosomal nucleolus organizing regions that contain the structural genes for ribosomal RNA can be abolished by proteolytic and oxidative treatments. Histone extraction has no effect. This indicates that reducing groups of non-histone chromosomal proteins are responsible for silver staining. Treatment with fluorescent sulfhydryl and disulfide specific reagents followed by silver staining demonstrates coincidence of silver dots and brightly fluorescent spots at the short arms of human acrocentric chromosomes where ribosomal RNA-genes are located. After treatment with cupric sulfite reagent in the presence of urea fluorescence and silver staining was no longer possible. Silver staining has been reported to be associated with ribosomal RNA-gene activity. Acrocentric chromosomes that are negative in silver staining also lack the brightly fluorescent spots. Therefore, we conclude that an abundance of protein-bound sulfhydryl and disulfide groups occur at nucleolar organizing regions with active genes. Differentially fluorescing spots could not be observed after staining with fluorescamine. So, either the sulfhydryl reagents used in this study are much more sensitive than fluorescamine to study protein distributions in cytological preparations, or our observations point to a local accumulation of some specific protein(s) rich in sulfhydryls. The presence of many sulfhydryl and disulfide groups at the nucleolus organizing regions seems suggestive of a great flexibility of protein(s) by transition of sulfhydryl groups to disulfide bridges and vice versa at these highly active regions of the genome.
103 citations
TL;DR: The present study shows that a brief fixation with 1% buffered formaldehyde followed by methanol: acetic acid (3 : 1) fixation yielded optimal preservation and silver staining of nucleoli.
85 citations
TL;DR: It is demonstrated that silver staining is associated with rRNA synthesis by directly demonstrating that it is located discretely and completely over the nucleolus.
65 citations
TL;DR: Prophase I meiosis was studied in the human oocyte and showed that, at pachytene, the ribosomal genes belonging to several chromosomes are gathered in the same nucleolar fibrillar center, where they are embedded in an argyrophilic protein.
Abstract: Prophase I meiosis was studied in the human oocyte obtained from 16- to 24-week-old fetuses. Electron microscopy and silver stainihg showed that, at pachytene, the ribosomal genes belonging to several chromosomes are gathered in the same nucleolar fibrillar center, where they are embedded in an argyrophilic protein. The nucleolus showed spontaneous segregation of its components due to temporary inactivation of the ribosomal genes. The fibrillar center, separated from the other nucleolar components, was penetrated as midpachytene by chromatin fibers containing rDNA emanating from one to three nucleolar bivalents. Thus, the ribosomal genes from 4-12 chromatids are temporarily juxtaposed inside the same structure. Such a structural arrangement is completely different from that observed in the pachytene-stage mouse oocyte, where two independent and active nucleoli, each displaying its own fibrillar center, were formed on the bivalents containing paired ribosomal genes. These different structural patterns are correlated with the high frequency of nondisjunction in the human oocyte and the relative infrequency of such in the mouse oocyte. The pattern observed in the human oocyte may be a cause of translocations.
62 citations
TL;DR: Chicken anti-mouse- RNP antibodies were able to react with cells from many different vertebrate species, showing a similar nucleus-restricted localization of the reacting sites, suggesting that these major hnRNA binding proteins may be found only in nuclei capable of RNA synthesis.
Abstract: Antibodies were raised in chickens against heterogeneous nuclear RNA (hnRNA)-binding proteins from 30S ribonucleoprotein (RNP) complexes of mouse Taper hepatoma ascites cell nuclei The antibody preparations were characterized for immunological specificity and purity by double-diffusion gels, binding to specific bands in SDS polyacrylamide gels, and crossed immunoelectrophoresis Antibodies raised against either whole 30S RNP complexes or purified RNP core proteins had a strong selective affinity for the four 34,000- to 40,000-dalton polypeptides which comprise the major structural proteins of hnRNP The intracellular distribution of 30S RNP antigens in mouse ascites cells was determined by indirect immunofluorescence microsacopy In interphase cells immunofluorescent sites were restricted to the nucleus, and nucleoli were free of fluorescence The chicken anti-mouse-RNP antibodies were also able to react with cells from many different vertebrate species, showing a similar nucleus-restricted localization of the reacting sites The antibodies also bound chick 30S RNP-proteins and reacted with the nuclei of chick cells An exception to this was the failure of the antibody to bind to adult chick erythrocytes, suggesting that these major hnRNA binding proteins may be found only in nuclei capable of RNA synthesis
59 citations
TL;DR: The distribution of nerve growth factor in rat pheochromocytoma cells has been studied with two different techniques: immunofluorescence and autoradiography and it was found that NGF is progressively internalized in the cytoplasmic compartment and eventually accumulates in the form of discrete dots around the nucleus.
Abstract: The distribution of nerve growth factor (NGF) in rat pheochromocytoma cells (clone PC12) has been studied with two different techniques: immunofluorescence and autoradiography. It was found that NGF is progressively internalized in the cytoplasmic compartment and eventually accumulates in the form of discrete dots around the nucleus. A fraction of the internalized NGF appears within the nucleoplasm, often contiguous with the nucleolus. It is suggested that cytoplasmic and perinuclear NGF may be be in contact with a pool of tubulin or actin-like proteins in their soluble or organized form and play a key role in the process of arrest of division and neurite growth.
55 citations
TL;DR: The appearance of more than one nucleolus per cell shortly after PHA administration suggests an activation of additional nucleolar organizer regions (NOR), which fuse to form one or two large nucleoli with nucleolonema, then transformed into “compact” nucleoli.
Abstract: The nucleoli of lymphocytes from circulating peripheral blood and from phytohaemagglutinin (PHA)-stimulated cultures (from 2 h–96 h) were studied using a silver method, RNA-specific fluorescent staining, and electron microscopy of ultrathin sections In peripheral blood about 75% of the lymphocytes have one “ring-shaped” nucleolus composed of a distinct fibrillar centre surrounded by a dense pars fibrillaris and little granular material; the remaining lymphocytes showing two or more small “ring-shaped” nucleoli With PHA stimulation, the number of cells with several nucleoli increases first (from 2 h–12 h) Next, cells containing one or, at most, two large nucleoli with nucleolonema devoid of fibrillar centers are seen (from 4 h on) 34 h after PHA, nucleoli of the “compact” type containing one or more fibrillar centres appear and comprise about 60% of the cells after 72 h The appearance of more than one nucleolus per cell shortly after PHA administration suggests an activation of additional nucleolar organizer regions (NOR), which fuse to form one or two large nucleoli with nucleolonema These are then transformed into “compact” nucleoli The fibrillar centers stain preferentially with silver They contain nonchromosomal proteins and may serve as stores for nucleolar proteins The fusion of activated NORs during the first cell cycle explains the relatively high frequency of satellite associations in first mitoses compared to later mitoses after stimulation
53 citations
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TL;DR: In this article, structural models for the organization of the peripheral nucleolar strands, the Balbiani ring (BR) transcription axes, and the tubular rough endoplasmic reticulum (RER) were formulated.
50 citations
TL;DR: The hypothesis that perichromatin granules represent storage forms of recently synthesized RNA, and that there may be at least two types (hnRNA and rRNA), is supported by observations.
50 citations
Journal Article•
TL;DR: In this work the structure of spontaneous nucleolar vacuoles is compared with that induced by drugs such as cordycepin, and FUdR and corresponds to a transient structure which not only shows higher metabolic activity but also supplies a storing and/or transporting mechanism for nucleolar products.
TL;DR: The technique of in situ hybridisation has been used to demonstrate that some wheat varieties have very different numbers of ribosomal RNA genes clustered in homologous nucleolus organisers.
Abstract: The technique of in situ hybridisation has been used to demonstrate that some wheat varieties have very different numbers of ribosomal RNA genes clustered in homologous nucleolus organisers. In these experiments the labelled probe was RNA synthesized in vitro using wheat ribosomal DNA cloned in a bacterial plasmid as template. Homologous nucleolus organisers were identified by the use of intervarietal chromosome substitution lines. A variety of rye has been shown to be heterozygous for the number of rRNA genes clustered in its major pair of nucleolus organisers. The in situ hybridisation technique has also been used to demonstrate an anomalous deletion of rDNA in an aneuploid derivative of Chinese Spring wheat.
TL;DR: A variety of 3H-labelled ribosomal gene probes were hybridized in situ to the nascent transcripts of lampbrush chromosomes from the crested newt, Tritums cristatus carnifex, finding that the nucleolus organizers were not sites of labelled loops in lampbrush transcript hybridizations.
Abstract: A variety of 3H-labelled ribosomal gene probes were hybridized in situ to the nascent transcripts of lampbrush chromosomes from the crested newt, Tritums cristatus carnifex. The probes were from Xenopus laevis and included rDNA isolated by CsCl gradient centrifugation, recombinant plasmids and purified restriction fragments of rDNA. All the probes gave essentially the same result. About 10–15 loop pairs were distinctly labelled in each preparation, almost all of them located on the heteromorphic arms (HTAs) of chromosome 1. Ribosomal gene probes were also hybridized in situ to the DNA of denatured mitotic chromosomes from some of the individuals used to provide lampbrush preparations. Minor, scattered sites of hybridization were found in the HTAs, but the main clusters of ribosomal genes were found on chromosomes 6 and/or 9, in agreement with previous determinations of nucleolus organizer position in this species. However, the nucleolus organizers were not sites of labelled loops in lampbrush transcript hybridizations. — We have incubated isolated lampbrush-stage nuclei in media containing α-amanitin and labelled RNA precursors. Although extrachromosomal nucleolar genes incorporated label, supposedly due to transcription by RNA polymerase I, no lampbrush loops were labelled. — It appears that in T. c. carnifex there are ribosomal gene sequences at the main nucleolus organizers and at a number of sites scattered along the HTAs. The ribosomal genes at the nucleolus organizers are not extended in the form of actively transcribing loops unlike the ribosomal sequences on the HTAs, which are heavily labelled in transcript hybridization. The ribosomal sequences on the HTAs appear not to be transcribed by the same RNA polymerase that transcribes the ribosomal genes of extrachromosomal nucleoli.
TL;DR: Nucleolar budding with formation of nuclear bodies displays the same intensity when cells are cultured in the presence of dibutyryl cyclic AMP (0.4 m M ) or prostaglandin E 2 (1 μM ), both of which are known to increase intracellular cyclicAMP concentration.
TL;DR: The heterogeneity of some low molecular weight nuclear and nucleolar RNA species resulted from a small number of mutations but much of the sequence was conserved, establishing that the complementarity of the conserved regions to HnRNAs, or protein binding sites, or both is of potential importance.
TL;DR: The present observations indicate that not all NORs are indicated by the morphological appearance of secondary constrictions, suggesting strongly that the NORs responsible for the minute nucleoli cannot be detected on the metaphase chromosomes.
Abstract: Allium sativum L. (2 n=16) had three types of clones with regard to the number of chromosomes carrying well-defined secondary constrictions: the first type had two secondary constricted chromosomes (type I), the second had three (type II) and the third had four (type III). Silver staining was applied to these three types of cells to determine the number of nucleolus organizing regions (NORs) per cell and to study the relationship between the morphological appearance of the secondary constrictions and the ability of the chromosomes to form nucleoli. Ag-positive regions appeared on two chromosomes in type I, on three in type II and on four in type III. The comparison of Giemsa and Feulgen stained chromosomes with the silver stained ones clearly indicated that the positive reaction with silver occurred exclusively on the secondary constricted regions that responded negatively to both Giemsa and Feulgen staining, indicating that the size of the achromatic secondary constrictions directly reflects the volume of the Ag-positive materials. However, all three types of clones had a maximum of four nucleoli at interphase. Of the four nucleoli, either two or one was extremely small (less than 1 μm in diameter) in types I and II respectively. The size variations of the other nucleoli seemed to be positively correlated with those of the Ag-positive regions. This and the observation that the maximum number of nucleoli per cell did not coincide with the number of Ag-positive regions on the metaphase chromosome complement suggest strongly that the NORs responsible for the minute nucleoli cannot be detected on the metaphase chromosomes. The present observations indicate that not all NORs are indicated by the morphological appearance of secondary constrictions.
TL;DR: Labelled RNA, transcribed in vitro from wheat ribosomal DNA cloned in a bacterial plasmid, has been hybridised to metaphase chromosomes of five diploid wheats, providing unequivocal evidence that these genotypes possess two pairs of nucleolus organizer chromosomes.
Abstract: Labelled RNA, transcribed in vitro from wheat ribosomal DNA cloned in a bacterial plasmid, has been hybridised to metaphase chromosomes of five diploid wheats. Autoradiography of the chromosomes has provided unequivocal evidence that these genotypes possess two pairs of nucleolus organizer chromosomes. The diploid wheat accessions used possess widely differing numbers of ribosomal RNA genes.
TL;DR: 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.
Abstract: 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 syntheses. The nucleolar changes are preceded by elevated litres 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.
TL;DR: It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase, and that in early prophase, the channels in theucleolonema of theucleolus are no longer occupied by Pale fibrills, but instead a long section of condensed chromosome is present, traversing the nucleolonema.
Abstract: The ultrastructure of telophase to interphase has been followed in a green alga, Spirogyra submargaritata. A series of changes transitional between the late anaphase chromatid, the decondensing chromatid of telophase, and the ‘pale fibrillar material’ occupying channels in the nucleolus at interphase have been demonstrated. Early stages in the regeneration of the nucleolus are described. It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase. It is also shown that in early prophase, the channels in the nucleolonema of the nucleolus are no longer occupied by pale fibrillar material, but instead a long section of condensed chromosome is present, traversing the nucleolonema. It is contended that these observations taken together constitute evidence that the pale fibrillar material of the nucleolus is the chromatin of the nucleolar-organizing region of the chromosome, expanded for transcription. A model of the nucleolus as it is seen in most electron-microscope sections, and as it can be interpreted in the light of present-day knowledge about it, is presented. A brief review of the relevant literature considers the views supporting the mode, and the contrary views, implicating the use of the term ‘nucleolar organizer’, that are still current at the present time.
TL;DR: The ribosome is not only the principal organelle in gene expression, but it is also one of the best-understood models of the structure, function, and coordination of a large number of genes operating in the eukaryotic cell.
Abstract: The biogenesis of ribosomes in eukaryotes involves the generation in the cell of the constituent core rRNA molecules and their interaction with about 80 distinct proteins to form the two mature ribosomal particles. Therefore, the ribosome is not only the principal organelle in gene expression, but it is also one of the best-understood models of the structure, function, and coordination of a large number of genes operating in the eukaryotic cell. Furthermore, ribosomes are made in the nucleolus, but they operate in the cytoplasm. In this respect, studies on the biogenesis of ribosomes contribute to our understanding of the molecular architecture of the cell.
TL;DR: The results lead one to regard the intercalary heterochromatin regions as “nests” comprising different types of actively transcribable genes, the composition of each nest varying in different stocks of D. melanogaster.
Abstract: Labelled RNA preparations (total newly synthesized RNA, as well as stable cytoplasmic RNA) isolated from a cell culture of D. melanogaster were hybridized in situ with polytene chromosomes. Apart from the nucleolus, in all cases the regions adjacent to the chromocentre in the polytene chromosomes and the intercalary heterochromatin regions in the X chromosome and the autosomes are the most intensively labelled. In the case of asynapsis of polytene chromosomes in heterozygotes the label is detected in a number of intercalary heterochromatin sites in one homologue only (“the asymmetrical label”). The same kind of radioactivity distribution in intercalary heterochromatin regions was observed after a hybridization of polytene chromosomes with cloned DNA fragments (Ananiev et al., 1978, 1979) coding for the abundant classes of messenger RNA (Ilyin et al., 1978) in a cultured D. melanogaster cells. In some regions of intercalary heterochromatin which do not contain these fragments the “asymmetrical” type of label distribution is observed after hybridization with cell RNA. — These results lead one to regard the intercalary heterochromatin regions as “nests” comprising different types of actively transcribable genes, the composition of each nest varying in different stocks of D. melanogaster.
TL;DR: The uptake of Ag-ions by isolated nucleoli of rat liver cells was studied and a mechanism for a preferential Ag-staining of the nucleoli is discussed.
Abstract: The uptake of Ag-ions by isolated nucleoli of rat liver cells was studied. Nucleolar proteins separated by electrophoresis were examined for selective silver-staining. A mechanism for preferential Ag-staining of the nucleoli is discussed.
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TL;DR: Sera from a patient with systemic lupus erythematosus gave granular cytoplasmic staining of hepatocytes, gastric chief cells, exocrine cells of the pancreas and submandibular glands, and cerebellar Purkinje cells, suggesting that the autoantibody is directed against ribosomal RNA and ribosome protein present in cytopLasmic polyribosomes, in RER and in nucleoli.
Abstract: Sera from a patient with systemic lupus erythematosus (SLE), tested by indirect immunofluorescence on frozen tissue sections, gave granular cytoplasmic staining of hepatocytes, gastric chief cells, exocrine cells of the pancreas and submandibular glands, and cerebellar Purkinje cells. In acetone-fixed monolayers of rat embryonic fibroblasts, 3T3 cells, mouse neuroblastoma cells, and cells from a human melanoma and colon carcinoma cell line, the sera stained perinuclear cytoplasmic granules which radiated out towards the cell periphery. More mature and differentiated fibroblasts from rat of human foetal lung showed staining of reticular cytoplasmic structures corresponding to phase-dense rough endoplasmic reticulum (RER). Nucleoli were prominently stained in all cultured cells. Serum absorption with ribosomes inhibited all antibody activity but absorption with RNA or with RNase-treated ribosomes resulted only in partial inhibition. Monolayers of RNase-treated fibroblasts gave weaker staining reactions compared to control untreated cultures. These observations suggest that the autoantibody is directed against ribosomal RNA and ribosomal protein present in cytoplasmic polyribosomes, in RER and in nucleoli.
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TL;DR: These nucleoli also contained epoxide hydrolase and NADPH-cytochrome c reductase activities, both of which were immunochemically identical to their respective microsomal counterparts.
Abstract: Significant amounts of cytochrome P -450 have been detected spectrally in purified nucleoli obtained from the livers of 3-methylcholanthrene-treated rats. Using monospecific antibody to microsomal cytochrome P -450 c ( P -448), we have shown that the nucleolar and microsomal enzymes are immunochemically identical. These nucleoli also contained epoxide hydrolase and NADPH-cytochrome c reductase activities, both of which were immunochemically identical to their respective microsomal counterparts.
TL;DR: DNA from both nuclear and nucleolar fractions was isolated and compared for the ability to direct RNA synthesis with homologous RNA polymerases and suggested that RNA polymerase I concentration rather than the nucleolar DNA template efficiency is responsible for the observed high rate of nucleolar transcription under the normal steady-state condition.
Abstract: When isolated rat liver nuclei and nucleoli are compared for RNA synthesis in vitro, the rate of nucleolar RNA synthesis is found to be more than 10 times higher. In order to understand this high rate of nucleolar transcription, DNA from both nuclear and nucleolar fractions was isolated and compared for the ability to direct RNA synthesis with homologous RNA polymerases. No difference between these two templates is evident. On the other hand, when the total nuclear and nucleolar RNA polymerases are isolated and compared on a per-unit-weight-of-DNA basis, it becomes clear that the nucleolus has a 10-fold higher RNA polymerase concentration than the nucleus. This result suggests that RNA polymerase I concentration rather than the nucleolar DNA template efficiency is responsible for the observed high rate of nucleolar transcription under the normal steady-state condition.
TL;DR: Ch Chromosomes and nucleoli have been examined during meiosis and postmeiotic nuclear divisions in the ascus, comparing heterozygous AR33 × N crosses with N × N and with crosses heterozygOUS for other interchanges.
Abstract: In rearrangement T(VL leads to IVL)AR33 the segment of chromosome 2 bearing the nucleolus organizer is translocated to the end of chromosome 4. When AR33 is crossed by Normal sequence (N), one third of the viable progeny contain a stable nontandem duplication with two organizers per nucleus. The organizer-deficient complementary products are inviable. Chromosomes and nucleoli have been examined during meiosis and postmeiotic nuclear divisions in the ascus, comparing heterozygous AT33 X N crosses with N X N and with crosses heterozygous for other interchanges. When AR33 is heterozygous, asci are of three types having the nucleolus organizer dupliciated in 0, 1 or 2 of the meiotic products. Frequencies of the ascus types are as expected from the known positions of rearrangement break points. Nucleoli formed by two organizers frequently fuse. Deficiency nuclei that contain no nucleolus organizer may form one or more small nucleolus-like bodies.
TL;DR: Diploid and triploid Xenopus can be easily and reliably distinguished by the size of their erythrocytes, and this method has several advantages over other methods, such as counting metaphase chromosomes and counting nucleoli.
Abstract: Diploid and triploidXenopus can be easily and reliably distinguished by the size of their erythrocytes. This method has several advantages over other methods, such as counting metaphase chromosomes and counting nucleoli. One problem with the latter method is the reduction in cells with a full complement of nucleoli when regenerating tissue is used.
TL;DR: The results indicated that nucleoli with fully intermingled fibrillar and granular components dominated in actively proliferating tissues whereas this type was almost lacking during the so-called dormant period.
Abstract: Monthly collections from October to April revealed seasonal alterations in the structure of the nucleoli of the microsporangiate strobili of the Scotch pine (Pinus sylvestris L.). By classifying the nucleoli in five types, two of them with subtypes, it was possible to list the amount and the sequence of the changes. The results indicated that nucleoli with fully intermingled fibrillar and granular components dominated in actively proliferating tissues whereas this type was almost lacking during the so-called dormant period. The wintertime nuclei, although remaining at interphases, also underwent structural alterations. In the early part of the winter, the most prominent feature was the loosening of the nucleolar structure, but this phenomenon decreased towards midwinter. The chromatin became strongly condensed and synchronous with this, the nucleolar organizer regions became visible as distinct, often ball-like entities. These were located at the surface of nucleoli, sometimes almost separated from them, and they were often partly, or fully, buried in condensed chromatin. Chromatin condensation relaxed transiently during the latter part of winter and at the same time, the granulation of the nucleoplasm increased. Nucleolar segregation disappeared before any mitoses began. The start of active cell divisions was accompanied by growth in the size of the nucleoli and by their increased stainability.
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TL;DR: The nucleolus organizer regions were studied in Nothoscordum fragrans, Liliaceae applying the technique of C-banding to distinguish the six acrocentric chromosomes into four types by the banding patterns in the long arms and also to observe in detail the nucleolu organizer regions and nucleoli.
Abstract: The nucleolus organizer regions were studied in Nothoscordum fragrans, Liliaceae (2n=19) applying the technique of C-banding. This technique allowed us to distinguish the six acrocentric chromosomes into four types by the banding patterns in the long arms and also to observe in detail the nucleolus organizer regions and nucleoli. The distal ends of the short arms of all six acrocentric chromosomes had a characteristic appearance at metaphase: completely condensing, fluff-like diffusing or amorphous loosening of the chromatin. These three characteristic formations seemed to represent a progressive alteration of the morphology of the short arms during metaphase. These regions were confirmed to be the nucleolus organizer regions since they were attached to the nucleoli at prophase. The frequencies of the three characteristic formations were studied for each type chromosome. There was a quantitative difference in the diffused or loosened chromatin for each type of chromosome. The possibility that this may reflect the size of the nucleolus organizer regions is discussed.