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1.
An ultrastructural study of the nucleolus of embryos of Paracentrotus lividus was carried out after treatment with Actinomycin D. It was shown that the fibrillar component of the nucleolus persists in the embryos treated with Actinomycin D in the mesenchyme blastula stage and fixed 24 and 48 hr after fertilization. The results are discussed in relation to the synthesis of RNA. 相似文献
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M Thiry S Schoonbroodt G Goessens 《Biology of the cell / under the auspices of the European Cell Biology Organization》1991,72(1-2):133-140
The fine structure of the insect Sf9 cell nucleolus has been investigated by means of different cytochemical and immunocytochemical techniques at the electron microscope level. Apart from a few perinucleolar condensed chromatin clumps, the insect cell nucleolus comprises two compartments. The first of these consists of a roundish compact zone formed of fibrillar material. The other is composed of fibrillar and granular structures organized into a network separated by interstitial spaces. But, unlike mammalian cell nucleoli, any fibrillar center has been observed in the Sf9 cell nucleolus, even after actinomycin D treatment. We also show that the compact fibrillar zone of Sf9 cell nucleoli contains silver-stainable material and DNA. In actinomycin D-treated cells, a preferential contact of this compact fibrillar zone with condensed chromatin has been visualized. Finally, silver-stainable material has been found to persist throughout the whole mitosis. These results suggest that the compact fibrillar zone at the insect Sf9 cell nucleolus should, at least partly, correspond to the fibrillar center of mammalian cell nucleoli. 相似文献
3.
Nucleologenesis: Composition and fate of prenucleolar bodies 总被引:21,自引:0,他引:21
Robert L. Ochs Michael A. Lischwe Eve Shen Robert E. Carroll Harris Busch 《Chromosoma》1985,92(5):330-336
A time course study was conducted on nucleologenesis after release from a mitotic block in the presence and absence of actinomycin D to determine the composition and fate of prenucleolar bodies (PNBs). Prenucleolar bodies, whether naturally occurring or induced by actinomycin D treatment, stain with silver and contain phosphoproteins B23 and C23, two of the major proteins of the interphase nucleolus as determined by double label immunofluorescence with specific antibodies. The nucleolus is formed by fusion of PNBs, which subsequently reorganize and form internal fibrillar and peripheral granular regions. Actinomycin D prevents fusion of PNBs, which are then randomly dispersed throughout the nucleus but they still contain proteins B23 and C23. These results demonstrate that the nucleolus is formed by fusion of prenucleolar structures whose biochemical composition resembles the mature nucleolus, since PNBs contain at least two of the major nucleolar proteins. 相似文献
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A LIGHT AND ELECTRON MICROSCOPE STUDY OF SMALL, SPHERICAL NUCLEAR BODIES IN MERISTEMATIC CELLS OF ALLIUM CEPA, VICIA FABA, AND RAPHANUS SATIVUS 总被引:5,自引:3,他引:2
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J. G. Lafontaine 《The Journal of cell biology》1965,26(1):1-17
Interphase, preprophase, and prophase nuclei of meristematic cells of Allium cepa, Vicia faba, and Raphanus sativus are characterized by the presence of spherical bodies approximately 1 µ in diameter. These structures are Feulgen-negative but stain metachromatically with azure B, as the nucleolus, following fixation with glutaraldehyde. At the ultrastructural level, they consist predominantly of fibrils estimated to be between 70 and 100 A in diameter which greatly resemble those found within certain zones of the nucleolus in these plant species. Moreover, in Allium cepa, these spherules often exhibit dense particles which are also found within the fibrillar zones of the nucleolus in this species. The observations that the bodies in question are frequently located at the surface of the nucleolus and moreover show cytochemical and ultrastructural similarities with this organelle suggest that they may originate from the nucleolus. However, the common association of the spherules with chromosome strands may indicate instead that these bodies represent extranucleolar ribonucleoprotein materials synthesized by specific chromosomal loci. 相似文献
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Numerous bodies resembling nucleoli, named “prenucleolar bodies”, were seen in the interphase nucleus of Xenopus laevis embryos between stages 7 and 11 of Nieuwkoop and Faber (1956) but not at stage 12. These bodies are composed of thick strands, 200 A in diameter, and apparently differ from the fibrillar component of the true nucleolus which consists of thin fibrils, 50 A in diameter. The granular component of the true nucleolus consists of fibers and granules which are both also 150–200 A in diameter, but which differ in chemical nature from the prenucleolar bodies. The granular component and fibrillar component are readily digested by RNase with or without pretreatment with trypsin, while the prenucleolar body is only digested with RNase after pretreatment with trypsin. This suggests that the prenucleolar body consists of strands of RNA coated with protein. At stage 9, another type of nucleolus-like body is formed, which is larger (2–2.6 μ in diameter) than the prenucleolar body (0.2–1 μ) and consists of thin fibrils of 50 A. This body resembles the fibrillar component of the true nucleolus in the size of the elemental fibrils as well as in its susceptibility to actinomycin D, RNase and trypsin. It seems to be a precursor of the true nucleolus and for this reason was named the “primary nucleolus.” From stage 9 to stage 10, each nucleus in the presumptive ectodermal and mesodermal areas contains 2 primary nucleoli together with multiple prenucleolar bodies. At stage 12, the prenucleolar body is not seen at all, but a new type of nucleolus-like body appears. There are usually 2 of these bodies in each nucleus, and they consist of 2 components: a network of 50 A fibrils, and a group of strands, 150–200 A in diameter, containing some granule-like elements. The former has the same susceptibility to actinomycin D, RNase and/or trypsin as the fibrillar component of the definitive nucleolus and the primary nucleolus, while the latter has the same susceptibility as the granular component of the definitive nucleolus. Thus, this body may 相似文献
7.
During meiotic prophase I the nucleolus of the mouse oocyte assumes a reticulate structure of ‘nucleolonema’ type. This change coincides with the appearance of several secondary fibrillar centres. The number of these centres at diplotene (97–113), largely exceeds that of nucleolar organizers (4c DNA = 20 NORs). The quantitatative analysis of autoradiographs after hybridization in situ with -3H-uridine labelled rRNA, enabled us to demonstrate that the multiplication of the fibrillar centres in mouse oocyte nucleolus during meiotic prophase I is not the result of an amplification of the rDNA. The number of silver grains in pachytene and diplotene nuclei was twice that counted for somatic cell and oogonium nuclei (2c DNA). 相似文献
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THE ORGANIZATION OF THE NUCLEOLUS IN MERISTEMATIC PLANT CELLS : A Cytochemical Study 总被引:3,自引:2,他引:1
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The architecture of the nucleolus in Allium porum and Triticum vulgare meristematic cells has been investigated by means of digestions with various enzymes. After staining with azure B at pH4, plant nucleoli exhibit lighter regions which, under electron microscopy, correspond to the fibrillar zones characterizing these organelles. Evidence is presented indicating that these latter zones contain coarse convoluted filaments quite similar to the loops first demonstrated by La Cour (24) and which are assumed to originate from the nucleolar-organizing chromosomes. These coarse, 0.2µ wide filaments are remarkably resistant to the action of deoxyribonuclease, ribonuclease, pepsin, trypsin, or of various combinations of these enzymes and, moreover, they show insignificant incorporation of labeled thymidine even after long exposure to this DNA precursor. The clearing action of pepsin on different regions of the nucleolus lends support to the hypothesis that an amorphous material or matrix pervades the mass of this organelle. This effect is particularly striking within the particulate nucleolar zones themselves. Both ribonuclease and trypsin disorganize the RNP (ribonucleoprotein) nucleolar particles. The effect of the latter enzyme on the RNP particles is taken to indicate that they contain proteins particularly susceptible to trypsin which are essential for maintenance of their morphological integrity. Trypsin also interferes with azure B-staining of the nucleolar mass as a whole and, according to radioautographic data, extracts RNA throughout this organelle. Accordingly, the hypothesis is considered that RNA is complexed with proteins not only within the particulate nucleolar portions, as is already well known, but also in the fibrillar zones. 相似文献
10.
Striking nucleolar lesions occur in cultured cells after exposure to supranormal temperatures. These lesions appear at 42°C and consist of a loss of the granular ribonucleoprotein (RNP) component and intranucleolar chromatin, and a disappearance of the nucleolar reticulum. The material remaining in the morphologically homogeneous nucleolus is a large amount of closely packed fibrillar RNP. The lesions remain identical as temperature increases to 45°C. These alterations are reversible when the cells are returned to 37°C and are associated with the reappearance of an exaggerated amount of intranucleolar chromatin and granular RNP. High-resolution radioautography indicates that after thermic shock nucleolar RNA synthesis is inhibited whereas extranucleolar sites are preserved: it also suggests that the granular RNP is reconverted to fibrillar RNP probably by simple unraveling. The results prove the existence of heat-sensitive cellular functions in the nucleolus which deal with the DNA-dependent RNA synthesis. The precise site of action is assumed to involve hydrogen bonds, resulting in configurational changes in nucleolar RNP and affecting the stability of the DNA molecule. The subsequent events in nucleolar RNA synthesis are discussed in light of the morphologic and biochemical effects of actinomycin D on the nucleolus. 相似文献
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黄瓜根尖分生组织细胞核仁超微结构类型及缺硼时的变化 总被引:1,自引:0,他引:1
硼是植物必需的一种微量元素,缺乏时植物根的生长被抑制。黄瓜根尖分生组织细胞核中核仁有四种类型。不缺硼的核仁中,丝状成分、粒状成分、丝状中心及核仁液泡能够明显地看到。缺硼的核仁中,丝状成分萎缩,变得粗短。看不见丝状中心、核仁液泡等。环形核仁中的中央大液泡变小。 相似文献
13.
REPOPULATION OF POSTMITOTIC NUCLEOLI BY PREFORMED RNA : II. Ultrastructure 总被引:3,自引:3,他引:0
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The reconstruction of the nucleolus after mitosis was analyzed by electron microscopy in cultured mammalian (L929) cells in which nucleolar RNA synthesis was inhibited for a 3 h period either after or before mitosis. When synchronized mitotic cells were plated into a concentration of actinomycin D sufficient to block nucleolar RNA synthesis preferentially, nucleoli were formed at telophase as usual. 3 h after mitosis, these nucleoli had fibrillar and particulate components and possessed the segregated appearance characteristic of nucleoli of actinomycin D-treated cells. Cells in which actinomycin D was present for the last 3 h preceding mitosis did not form nucleoli by 3 h after mitosis though small fibrillar prenucleolar bodies were detectable at this time. These bodies subsequently grew in size and eventually acquired a particulate component. It took about a full cell cycle before nucleoli of these cells were completely normal in appearance. Thus, nucleolar RNA synthesis after mitosis is not necessary for organization of nucleoli after mitosis. However, inhibition of nucleolar RNA synthesis before mitosis renders the cell incapable of forming nucleoli immediately after mitosis. If cells are permitted to resume RNA synthesis after mitosis, they eventually regain nucleoli of normal morphology. 相似文献
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Three-dimensional ultrastructure and quantitative analysis of the human Sertoli cell nucleolus 总被引:1,自引:0,他引:1
C Cataldo C Souchier A Stahl 《Biology of the cell / under the auspices of the European Cell Biology Organization》1988,63(3):277-285
The nucleolus of the human Sertoli cell displays a spontaneous segregation of its components and has only one or 2 large fibrillar centers. The 3-dimensional reconstruction and quantitative analysis of its components was undertaken using a Quantimet 900 image analysis system in order to define the spatial relationships between the dense fibrillar component and the fibrillar center and especially to investigate whether threads of dense fibrillar component exist independently, without being linked to a fibrillar center. Our 3D reconstructions demonstrated that the dense fibrillar threads or sheets were never independent of fibrillar centers. These structures belonged to a continuous network that joined the layer of dense fibrils surrounding the fibrillar center. When the nucleolus contained 2 different-sized fibrillar centers, quantitative analysis showed that there was a proportional relationship between the volume of the dense fibrillar component and the volume of the fibrillar center. These data, compared with those previously obtained by means of autoradiographic techniques, suggest that the rDNA-containing chromatin passes through the fibrillar center and unwinds from there into the dense fibrillar component. 相似文献
16.
Pierre Mineur Abdelilah Jennane Marc Thiry Roger Deltour Guy Goessens 《Journal of structural biology》1998,123(3):199-210
We have investigated the precise location of DNA within the meristematic cell nucleolus ofZea maysroot cells andPisum sativumcotyledonary buds, in the course of their activation and induced inactivation following a subsequent treatment at low temperature. For this purpose, we combined the acetylation method, providing an excellent distinction between the various nucleolar components, with thein situterminal deoxynucleotidyl transferase-immunogold technique, a highly sensitive method for detecting DNA at the ultrastructural level. In addition to the presence of DNA in the condensed chromatin associated with the nucleolus, we demonstrated that a significant label was detected in the nucleolus of quiescent cells in both plant models. Evident labels were also found in the dense fibrillar component of actived nucleoli. Whereas in inactivated nucleoli no significant label was observed within the dense fibrillar component, an intense label was seen over the large heterogeneous fibrillar centres only during inactivation. The granular component was never significantly labelled. These results appear to indicate that the DNA present in the dense fibrillar component of activated nucleoli withdraws from this structure during its inactivation and becomes incorporated in the large fibrillar centres. These observations suggest that in plant cells inactivation of rRNA genes is clearly accompanied by changes in the conformation of ribosomal chromatin. 相似文献
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用透射电镜观察到MGC-803细胞的核仁是网织型的,在网眼内分布有电子密度低的纤维中心。MGC-803细胞经丁酸钠作用后,其核仁的类型发生了改变,多呈环型的,核仁的中央有一个大的纤维中心;纤维中心和银染颗粒的大小和数目明显减低;用图像分析仪测得核仁银染蛋白所占面积与核总面积的比值也明显降低。结果提示:丁酸钠可能通过抑制rRNA合成和rDNA转录活性调控MGC-803细胞的增殖。 相似文献
20.
O. G. Leonova B. P. Karadzhyan Yu. F. Ivlev Yu. L. Ivanova V. I. Popenko 《Molecular Biology》2012,46(2):218-225
According to our computer modeling data obtained earlier, nucleoli in interphase ciliates Didinium nasutum are complex netlike structures, in which the trabeculumor lamella-shaped fibrillar component is located on the periphery,
and the granular component in the central part of the nucleolus. Chromatin bodies connected with nucleoli act as the nucleolar
organizers in D. nasutum. In the present work, the arrangement of all chromatin bodies, which could correspond to nucleolar organizers by morphological
criteria, is studied by means of a 3D-reconstruction. It is shown that all of these chromatin bodies are localized outside
the nucleoli, on the fibrillar component’s periphery. Even those chromatin bodies which appeared to be completely surrounded
by the fibrillar nucleolar component on single ultrathin sections are actually settled down in nucleolus cavities open to
the nucleoplasm. This proves that the RNA processing in D. nasutum nucleoli is directed toward the center of nucleoli, where the granular component is located. The analysis of the nucleolar
chromatin distribution made it possible to conclude that different parts of the complex interfase netlike nucleoli of D. nasutum have approximately the same activity. 相似文献