Nucleolar Ultrastructure Research Articles

Intracranial implants of actinomycin-D: effects on sexual behavior and nucleolar ultrastructure in the rat.

It was previously shown that 0.18 µg actinomycin-D (Act-D) in bilateral implants into the preoptic area (POA) significantly inhibited lordosis behavior in the ovariectomized estrogen-primed rat [Quadagno et al., 1971]. This experiment was repeated in order to correlate the suppression of steroid-induced sexual behavior with certain ultrastructural features of cells in the POA. Cells in the POA of animals receiving Act-D showed profound structural changes in nucleolar morphology which are typical of cells altered by Act-D treatment. It is suggested that Act-D is producing a specific effect, i.e. blocking the DNA-dependent synthesis of messenger RNA, rather than a nonspecific effect due to cytotoxicity.

Studies on the nuclear and nucleolar ultrastructure in differentiating and differentiated human sebaceous cells

To provide more information on the regressive nuclear as well as nucleolar changes in degenerating and differentiating cells, the human sebaceous cells were studied by means of usual electron microscopic procedures. The ultrastructural nuclear changes in differentiated sebaceous cells were characterized by the chromatin condensation, increased number of nuclear bodies and perichromatin as well as interchromatin granules. In addition, nuclei of these cells also contained large light areas which were composed of fine filaments similar to those present in nuclear bodies. Nucleoli in partially differentiated sebaceous cells were composed of nucleolonemas. Fully differentiated cells contained ringshaped nucleoli as well as small compact nucleoli of fibrillar appearance or with segregation of nucleolar components. The presence of fine filamentous shell around the small compact nucleoli with segregation of nucleolar components suggested the possibility of the existence of transitional forms between such nucleoli and large nuclear bodies containing dense granules and fibrillar structures similar to the nucleolar components.

Comparison of the effects of coxsackievirus A9 and of actinomycin D on the nucleolar ultrastructure of monkey kidney cells

First signs of cytopathogenic effect in monkey kidney cells after infection with Coxsackievirus A9 are visible in the nucleolus. The lesions consist in a characteristic segregation of the nucleolar constituents. The changes appear 2–5 hours after infection. The disruption of the nucleoli is completed by 14 hours after infection. These nucleolar alterations are identical to the changes induced by actinomycin D. The biochemical data on the action of the two agents are compared.

Alteration of nucleolar ultrastructure in iris epithelial cells during initiation of Wolffian lens regeneration.

AbstractMorphological aspects of nucleoli of iris epithelial cells participating in Wolffian lens regeneration in the adult newt (Triturus viridescens) were studied with electron and phase‐contrast microscopes at various times after lens removal. In normal condition, the nucleoli appear as small, compact bodies composed of fibrous elements. The granular element is often lacking, but when present, is sparse and located at the periphery of the organelle. Within two days after lens removal, the size of the nucleolus increases, and its shape becomes complex and diversified. The granular element increases in absolute as well as relative amount. Granular and fibrous components become intermingled and together form the fibrogranular region. Portions of this region often project from the nucleolus as coarse threadlike extensions that become a prominent feature. Morphogenesis of the organelle continues during the subsequent two days. In parallel with these structural changes, the number of nucleoli per nucleus and the frequency of nuclei containing nucleoli increases. All these changes start in the nondividing phase of the iris epithelium before induced cell division. These changes in nucleoli are the earliest so far observed in iris epithelial cells after lens removal, and coincide in time with the activation of ribosomal RNA synthesis previously observed in this system.

Studies on the ultrastructure of nucleoli in human smooth muscle cells

Nucleoli were studied in smooth muscle cells in the stroma of nontumorous portions of prostate glands from patients with prostatic cancer without previous antitumor therapy to provide more information on the presence and ultrastructure of ring-shaped nucleoli in human cells, The results have shown that smooth muscle cells contain nucleoli with varying amounts of nucleolonemas as well as ring-shaped nucleoli which were not previously reported in these cells. Large nucleoli with or without well defined nucleolonemas were usually observed in less mature forms of smooth muscle cells which were rich in ribosomes. In contrast, ring-shaped nucleoli were mostly present in highly differentiated and mature smooth muscle cells characterized by a large number of myofilaments and a low concentration of ribosomes in their cytoplasm. The ultrastructural morphology of ring-shaped nucleoli in these cells did not differ from that in mature lymphocytes, differentiated lymphosarcoma cells, plasmacytes, monocytes, myeloblasts and promyelocytes. In addition, ring-shaped nucleoli were also noted in some endothelial cells of small capillaries and fibrocytes. The finding of ring-shaped nucleoli in these different cell types apparently indicates that the presence and formation of such nucleoli represents a general phenomenon that reflects a reduced but continuing synthesis of ribosome precursors in the nucleolus.

On the ultrastructure of nucleoli in human leukemic myeloblasts

The ultrastructure of nucleoli was investigated in myeloblasts and promyelocytes of untreated patients with acute myeloblastic leukemia. These myeloblasts and promyelocytes contain compact nucleoli, nucleoli with nucleolonemas and ring-shaped nucleoli have been observed. In the latter nucleoli, dense chromatin clusters were found adjacent to the central core. In the peripheral region of the ring-shaped nucleoli, a thin discontinuous layer of granular elements was noted in the largely fibrillar area. The ultrastructure of the ring-shaped nucleoli of the leukemic myeloblasts is very similar to that previously described in mature lymphocytes; these findings suggest the nucleolar function is reduced in some myeloblasts in acute leukemias.

Changes in nucleolar ultrastructure during amphibian development

Changes in nucleolar ultrastructure during amphibian development

The effects of fluorouracil and actinomycin, single and combined, on the nucleolar ultrastructure of various tissues of the rat.

5-fluorouracil and actinomycin D were given, single and combined, to rats. The nucleolar ultrastructure was examined in liver, pancreas, spleen, kidney cortex, adrenal cortex, in epithelial and smooth muscle cells of the small intestine and in the Purkinje cells of the cerebellum. 5-fluorouracil, given alone, provoked changes in all tissues examined. Actinomycin D, given alone, gave changes in all tissues examined, except the cerebellum. Treatment with fluorouracil prior to actinomycin delayed and modified the effect of the latter drug in all tissues examined.

Isolation of nucleoli in a medium containing spermine and magnesium acetate

Studies are presented on the effects of polycations on the ultrastructure of nucleoli. When tumor cells were homogenized in 0.25 M sucrose lacking divalent ions, polyamines or histones, the nucleolar structure was difficult to identify and nucleolar components appeared to be dispersed. Addition of arginine-rich histones and some slightly lysine-rich histones as well as polyamines to the sucrose medium used for homogenization preserved nucleolar structure with respect to ultrastructural morphology. Addition of protamines, spermine and spermidine to the homogenization medium containing sucrose produced compact and dense nucleoli. These results suggested that a practical procedure for isolation of nucleoli could be developed in which the polyamines were used and a combination of 15 m M Mg 2+ and 0.25 m M spermine was found to provide a satisfactory addition to 0.25 M sucrose for maintenance of nucleolar integrity. Nucleoli isolated from liver cells homogenized in a medium containing this combination were found to be similar in morphology and composition to those obtained with the sucrose medium containing calcium ion. The yields were essentially the same.

Radioautographic, ultrastructural and biochemical studies on the effect of fluorouracil on the RNA synthesis in ther liver of rats.

The effects of fluorouracil and uracil on the ultrastructure and RNA synthesis in the liver of rats have been studied. High doses of uracil, contrary to fluorouracil, had no effects on nucleolar ultrastructure. Fluorouracil, even in low doses, depressed the RNA synthesis as studied after cytidine-3H administration. In the radioautographs the depression was especially seen to affect the cytoplasmic labelling. The biochemical analysis showed signs of a depression of ribosomal RNA synthesis and a block or delay in the maturation of ribosomal RNA. Repeated, high doses of uracil also depressed the RNA synthesis but there did not seem to be any delay in the maturation of ribosomal RNA. The results suggest that fluorouracil may affect the RNA metabolism in the nucleoli.

Changes in nucleolar ultrastructure associated with differentiation in the root tip

The development of the nucleolus in the root apex of Plantago ovata has been studied primarily at the ultrastructural level. Nucleolar volumes in the quiescent center and selected regions of the root cap, cortex, and epidermis correlate qualitatively with cytoplasmic basophilia and mitotic frequency. The small nucleoli of the quiescent center have been shown by means of serial sections to contain intrusions of heterochromatin into the internal fibrillar zone. The number of intrusions corresponds to what would be expected if each represents the attachment of a nucleolar organizing chromosome. Differences in the chromosomal-nucleolar junction following different fixation procedures are described. One per cent collidine-buffered OsO 4 routinely produces a sharp nucleolar image with the fibrillar and ribosomal regions clearly distinguished. Other fixatives such as acrolein-glutaraldehyde followed by OsO 4 produce a more diffuse nucleolar image but make much clearer the differences between chromatin and nucleolar heterochromatin. Where cortical and epidermal nucleoli are largest (10–12 times the volume of those in the quiescent zone) the ribosomal regions are intermingled with the fibrillar regions and the general structure is less compact. Often present is a large central lacuna containing fibrils of a chromatin-like character as well as what appear to be free ribosome-like particles. As division ceases and cells increase in size, the vacuoles occupy an increasing proportion of the cell volume, the nucleoli return to a size and arrangement like that in the quiescent center.

Ultra-structure of Nucleoli and Chromosomes in Normal and X-irradiated Liver Cells

Ultra-structure of Nucleoli and Chromosomes in Normal and X-irradiated Liver Cells

The ultrastructure of nucleoli and chromosomes during the early stages of liver regeneration and the changes produced in these structures by X radiation

A method of tissue preparation for electron microscopy is described which allows the observation of more nuclear structure than has previously been reported. Regenerating rat-liver cells were used for this study. During the early stages of regeneration the nucleolar size was found to be much greater than normal, although nucleolonema fibres and pars amorpha were still present. At 16 to 18 h after operation, however, when there is considerable production of new a-cytomembranes in the tissue, much of the material of the pars amorpha was lost from many cells, and the nucleoli consisted solely of nucleolonema fibres. Later the pars amorpha was re-formed, but just before the start of mitosis at 25 to 26 h after operation, many of the nucleoli became very irregularly shaped. The various mitotic stages seen in liver cells with the electron microscope were recognizably similar to those previously seen in living mammalian cells with the light microscope. In the earliest stages of prophase the chromosomes appeared as strands approximately 1000 A in diameter, which were made up of thin fibres approximately 100 A in diameter. By mid-prophase these strands could be seen running diagonally across the chromosomes in a manner suggestive of coiling, but by late prophase this coiling was no longer visible and the chromosomes appeared as homogeneous masses of fibres 100 A in diameter. The double nature of the chromosomes was, however, evident during metaphase. Telophase nuclei were seen to contain fibrous inclusions approximately 1000 A in diameter which it is suggested may represent stages in the re-formation of the nucleolus after mitosis. The effect of X radiation on the ultrastructure of the nuclear components of regenerating liver cells was also studied in these experiments. With small doses (450 r) no ultrastructural changes were found in the chromosomes during cell division, but some changes were visible in the nucleoli just prior to mitosis. Larger doses (2000 r) caused chromosome fragmentation and a loosening of the fibrous chromosome structure. In telophase it was found that when the separation of the two daughter nuclei is inhibited or delayed, the nuclear membrane re-forms around the two partially separated chromosome masses.

Ultrastructure of Nucleoli in Oocytes of Patella coerulea

A SPECIAL nucleolus, called ‘Primarnucleolus’ by Jorgensen1, is always present during the growth of oocytes of Patella coerulea, while other nucleoli, called ‘Amphinucleoli’ by the same author gradually make their appearance. The ‘Primarnucleolus’ stains2 red with Mallory's method and does not show the nucleolonema of Estable and Sotelo3, while the ‘Amphinucleoli’ stain red at first, become blue later, show nucleolonemal elements and finally adhere to the nuclear membrane, where they gradually disappear. Previous research4 suggested that this transition from red to blue might be due to a passage from a dense to a fluid state, which allows nucleolar substances to pass the nuclear membrane. No explanation was given of the presence of the nucleolonema in amphinucleoli and of its absence from the primary nucleolus. Electron microscope observations have been undertaken in order to check these results.

Electron microscope researches on the ultrastructure of nucleoli in animal tissues.

On the basis of electron microscopy of nucleoli in various physiological stages of similar and different cells, it is assumed that the nucleolonemata appear for the first time in the pre-mitotic stage and subsequently the nucleolus-associated body makes its appearance.