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1.
Summary The nuclear apparatus ofRemanella granulosa has been investigated using conventional TEM methods and Bernhard's technique of preferential RNP staining. This species has two (rarely three) macronuclei and a single micronucleus (rarely two micronuclei). The nuclei always form a single group.The macronuclei contain a fibro-granular matrix resistant to EDTA destaining, and several nucleoli and chromatin bodies. The chromatin bodies are readily bleached with EDTA and are often clustered, or even fused, forming chromocenters. The nuclei are of the compact concentric type. Some macronuclei contain nuclear bodies, as finely fibrous spheres or bundles of coarse fibers, or both. Neither type of nuclear body is destained with EDTA. The spheres are frequently associated with nucleoli. There is no evidence of any transition between the two types of nuclear bodies. The macronuclear envelope contains numerous pore complexes and is strengthened with an electron dense layer. The micronucleus is filled with spongy condensed chromatin and surrounded by an envelope with occasional pores. This nucleus lacks nucleoli and nuclear bodies.  相似文献   

2.
I B Raikov 《Tsitologiia》1975,17(9):1009-1017
The nuclear apparatus of Loxodes magnus Stokes (Holotricha) consists of numerous macronuclei which belong to the diploid type and never divide, and of numerous micronuclei. No nuclear groups exist; individual nuclei often lie in cytoplasmic islets surrounded by large lacunae of the smooth endoplasmic reticulum. Interphasic micronuclei have two-membraned envelopes with numerous pores, usually lined at the cytoplasmic side with a layer of vacuoles, channels, or flattened vesicles of the smooth endoplasmic reticulum. The chromatin of the micronuclei consists of anastomosing threads, 0.1--0.2 mum wide, between which several nucleolus-like bodies of microfibrillar structure occur. Adult macronuclei have a similar nuclear envelope and a similar system of vacuoles, channels, and flattened agranular cisternae outside it. The macronucleus contains a single large composite nucleolus with 3 or 4 fibrillar cores inside the common granular cortex. The fibrillar cores are pierced by channels containing nucleolar organizers in the form of strands of condensed chromatin. The peripheral zone of the macronucleus is filled with decondensed chromatin fibrils and contains a number of small chromocenters and several aggregates of RNP granules. No protein inclusions (spheres) have been observed in Loxodes macronuclei. The macronuclear anlagen, developing in the cycle of every cell division, show progressive decondensation of the chromosomes and formation of several nucleoli, each with its own organizer. Later on, the nucleoli fuse into a single nucleolus. The small chromocentres are the last to form.  相似文献   

3.
ABSTRACT. The nuclear apparatus of Homalozoon vermiculare consists of a single moniliform macronucleus and about 25 micronuclei. The number of macronuclear segments depends (i) on the number of divisions of individual segments during the interphase and (ii) on the number of segments that arise prior to cytokinesis from the (temporary) filiform macronucleus. Precytokinetic changes of the macronucleus involve the fusion of individual segments followed by contraction and subsequent elongation of the entire macronucleus. The chromatin bodies uncoil into fine fibrils during macronuclear contraction. At the time when the division furrow appears, the macronucleus starts to renodulate. The interphase segment contains a more or less reticulated chromatin body partly attached to the nuclear envelope and about 30 polymorphous nucleoli. The latter consist of the pars granulosa, the pars fibrosa, and an additional fibrillar component. The nucleoli undergo drastic changes prior to division and the granular component disappears completely during macronuclear condensation. On the average, the macronucleus contains a 3,400-fold amount of DNA compared with a haploid micronucleus, but the intraspecific differences in the DNA content of the entire macronucleus are extremely large. In contrast, DNA content and size of an individual segment of the macronucleus are precisely regulated during interphase.  相似文献   

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The macronuclei of synchronously dividing mass cultures of Tetrahymena pyriformis (strain WH6) were examined with the electron microscope for changes during two division cycles. Samples were prepared at 30-minute intervals for a period of 8½ hours which included the time required to induce synchrony by five heat shocks (4½ hours). The interphase macronucleus contains peripheral, crescent-shaped nucleoli and evenly distributed chromatin bodies. Centrally located RNA bodies, composed of fibers, appear 1 to 2 hours following the initial heat shock. They are completely destroyed with ribonuclease whereas the nucleoli are only partially so. Following the third heat shock the RNA bodies move to the periphery and disintegrate; the nucleoli aggregate and form blebs which protrude into the cytoplasm where they appear to pinch off and may contribute to the cytoplasmic ribonucleic acid. Cytokinesis does not occur at this time. Instead the nuclear events are repeated during the 4th and 5th hours, even though the heat shocks are terminated at 4½ hours. Cytokinesis takes place at about 6 hours. The second division occurs about 2½ hours later during which all the macronuclear events noted above are repeated.  相似文献   

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8.
This paper reports new observations obtained from a study of macronuclear fine structure throughout various stages of the cell division cycle of Euplotes. Study of the ultrastructural organization of the macronuclear chromatin indicates that much of the chromatin is organized into continuous masses, portions of which appear to be attached to the nuclear envelope. The macronuclear envelope appears unchanged in the region of a replication band, and apparent attachments of the chromatin to the inner membrane of the nuclear envelope are maintained in the reticular and diffuse zones. Intranuclear helices were never observed in the diffuse zone. During macronuclear division, linear elements (fibrils or microtubules) were observed in close association with both chromatin bodies and nucleoli. The ultrastructural data suggest that the intranuclear linear fibrils have two functions: elongation of the dividing nucleus, and attachment of chromatin bodies and nucleoli to the envelope. The significance of these observations for macronuclear division and chromatin segregation is considered.  相似文献   

9.
Electron microscopic study of chromatin organization in isolated macronuclei of a ciliate Bursaria truncatella showed macronuclear chromatin to be organized in compact clumps 120--180 nm in diameter linked with each other by one or several chromatin fibres. Macronucleus being dispersed in a solution of low ionic strength, radial loops basically of nucleosomal structure start appearing around chromatin clumps. Long-time dispersing of macronuclear chromatin brings complete decompactization of chromatin clumps into a set of nucleosome fibres. The way the fibres of interphase chromatin are packed in a chromatin clump is discussed.  相似文献   

10.
A new method for isolation of the constitutive heterochromatin (chromocenters) from interphase nuclei of mouse liver has been developed. This method allows separation of chromocenters of different size. Chromocenter fractions are essentially free of nucleoli and other contaminants. In contrast to nuclei and nucleoli, the chromocenter fraction is characterized by simpler protein composition, this fraction having a reduced number of proteins (especially high molecular weight proteins). Chromocenters contain all histone fractions; however, the relative proportion of histone H1 is lower and histone H3 is higher than in the total nuclear chromatin. The amount of non-histone proteins of 51, 63, 73, and 180 kD is higher in the chromocenter fraction than in nuclei and nucleoli. The use of immunocytochemistry and immunoblotting methods revealed the presence of the specific kinetochore component, CENP A protein. This suggests tight association of some molecular kinetochore components with chromocenters in the interphase.  相似文献   

11.
赫杰  苗桂英  赵海成 《植物研究》2002,22(1):26-29,T001
运用Bernhard染色方法研究了小麦根端分生组织细胞核仁在细胞周期中的变化。结果显示,间期核仁染色很深,能够区分出纤维中心(FC)、致密纤维组分(DFC)和颗粒组分(G),而染色质被漂白,在染色质间可以观察到细小的RNP颗粒。进入前期,在染色质的边缘有小的RNP颗粒分布。中期,染色体周边分布着类似于间期核仁的深染的大RNP颗粒,形成一个不完全连续的“鞘”状结构;在染色体内部看不到类似核仁的深染颗粒。到了后期时,仍可见RNP“鞘”状结构的存在。进入末期,这些RNP植物逐渐由“鞘”脱离,最后参与新核仁的形成。这些结果表明,核仁解体后的物质直接转移到了中期染色的表面,并形成不连续的表层,没有进入染色体的内部。  相似文献   

12.
In isolated interphase mouse liver nuclei after hypotonic treatment only the chromocenters belonging to the pericentromeric heterochromatin remain in dense form while the main mass of a chromatin is completely decondensed. The centromeric nature of these chromocenters is demonstrated by their capability for C-banding and for hybridization with a satellite mouse DNA.  相似文献   

13.
During conjugation in the binucleate ciliate, Tetrahymena thermophila, the old macronucleus is eliminated as new macronuclei and micronuclei are ontogenetically derived from the zygote nucleus. The mechanism of programmed nuclear elimination in ciliates may be related to the mechanism of apoptosis in higher organisms since its chromatin undergoes major condensation, its DNA is digested into nucleosome-sized fragments, and it stains positively for TUNEL. The present study explores whether caspases are involved in programmed macronuclear degradation in Tetrahymena. We show here that caspase-like activity is detectable using two specific colorimetric substrates, and that the activity is reduced with specific caspase inhibitors. In addition, using the fluorigenic substrate PhiPhiLux, active caspase-like activity is detected in living cells, localized to cytoplasmic vesicles; activity is not detected in pre- or post-condensed macronuclei. Finally, three different inhibitors of caspase activity cause a block to macronuclear chromatin condensation and elimination. Therefore, a caspase-like enzyme activity is necessary for regulating macronuclear elimination in Tetrahymena. These data support the possibility that macronuclear elimination is related, evolutionarily, to regulated cell death in multicellular organisms.  相似文献   

14.
The Feulgen and Rossenbeck staining procedure reveals in all embryonic and adult cell types of the quail (Coturnix coturnix japonica) one or several chromatin condensations in the interphase nucleus. The Unna-Pappenheim technique, combined with RNAase treatment according to Brachet, shows that these chromatin masses are associated with the nucleolar RNA. Electron microscopic studies confirm this observation and the EDTA preferential staining procedure for RNP according to Bernhard makes it possible to distinguish three main types of nucleoli in the various tissues of the quail showing different patterns of RNA and DNA relationships. The functional significance of the large amount of nucleolus-associated chromatin in the quail, and of the more or less intimate relationships between RNA and DNA in the various types of nucleoli are discussed.  相似文献   

15.
During conjugation, the micronucleus of Tetrahymena thermophila undergoes five consecutive nuclear divisions: meiosis, third prezygotic division (pregamic mitosis) and two postzygotic mitoses of the synkaryon. The four products of the synkaryon differentiate into macronuclear anlagen and new micronuclei and the old macronucleus is resorbed. The protein synthesis inhibitor cycloheximide, applied during conjugation, induced several developmental blocks. Pairs shifted to the drug during early meiotic prophase (stages I–III) were arrested at prophase. Cycloheximide applied to cells at pachytene (stages IV-VI) to metaphase arrested the conjugants at the stage of modified prometaphase/metaphase with overcondensed, swollen bivalents. In contrast to other systems, in the presence of cycloheximide, separation of chromatids, decondensation of chromosomes and exit from metaphase I were inhibited in both diploid and haploid cells. Pairs shifted to the drug after metaphase I were arrested at postmeiotic interphase after completing one nuclear cycle. The same rule applied to the subsequent cycle; then cells were arrested at the stage of pronuclei, and those pairs with functional pronuclei and synkarya were arrested at the stage of two products of the first postzygotic division (pronuclei were not arrested in nuclear transfer and karyogamy). Only pairs with two products of the first postzygotic division were arrested at the same stage after the cycloheximide treatment. Pairs shifted to cycloheximide during the second postzygotic division were arrested in development of macronuclear anlagen and resorption of old macronuclei. The postmeiotic conjugants pulse-treated with cycloheximide (2 h) yielded heterokaryons retaining parental macronuclei (i.e. they exhibited macronuclear retention).  相似文献   

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17.
A method for the isolation of micronuclear DNA from Paramecium tetraurelia has been developed. After cell lysis, a low speed centrifugation at 1,000 g is used to remove all of the unbroken cells and macronuclei and approximately two thirds of the macronuclear fragments. Next a higher speed centrifugation of 9,000 g sediments the micronuclei and frees them from small particulates and soluble constituents. Advantage is then taken of the fact that micronuclei have a lower density than do macronuclear fragments in 45%–60% Percoll. Micronuclei float to the top during centrifugation at 24,000 g , while macronuclear fragments sediment. After several cycles of centrifugation in Percoll, the micronuclei, although heavily contaminated with cytoplasmic components, are essentially free of macronuclei and macronuclear fragments. Micronuclear DNA can then be extracted from the suspension. The whole procedure is very rapid and in about an hour micronuclear and macronuclear DNA can be separated. About 2 μ g of micronuclear DNA can be obtained from 6 times 107 paramecia. We find that there are internal sequences in the micronuclear A gene DNA in wild type cells which are eliminated when the micronuclei develop into macronuclei. They yield unique restriction fragments for micronuclei and macronuclei. Therefore the purity of the preparations is easily monitored by probing Southern blots of restriction enzyme-digested DNA with the cloned A gene. No differences have been found between the micronuclear A gene in wild type and the d48 mutant.  相似文献   

18.
We developed a modified immunofluorescence protocol that permitted visualization of microtubules inside the macronucleus of the ciliate Tetrahymena. Although the amitotically dividing macronucleus lacks a spindle, an elaborate system of microtubules is assembled inside the macronucleus and between the macronucleus and the cortex. Microtubules could not be detected inside the interphase macronuclei. The early stage of macronuclear division was associated with the assembly of short macronuclear microtubules that localized randomly. The intramacronuclear microtubules were subsequently organized in a radial manner. During elongation of the macronucleus, the distribution of macronuclear microtubules changed from radial to parallel. During constriction of the macronucleus, dense and tangled macronuclear microtubules were detected at the region of nuclear constriction. In the cytosol, microtubules were linking the macronucleus and cell cortex. During recovery after drug-induced depolymerization, microtubules reassembled at multiple foci inside the macronucleus in close proximity to the chromatin. We propose that these microtubules play roles in chromatin partitioning, macronuclear constriction, and positioning of the macronucleus in relation to the cell cortex.  相似文献   

19.
A method for the isolation of micronuclear DNA from Paramecium tetraurelia has been developed. After cell lysis, a low speed centrifugation at 1,000 g is used to remove all of the unbroken cells and macronuclei and approximately two thirds of the macronuclear fragments. Next a higher speed centrifugation of 9,000 g sediments the micronuclei and frees them from small particulates and soluble constituents. Advantage is then taken of the fact that micronuclei have a lower density than do macronuclear fragments in 45%-60% Percoll. Micronuclei float to the top during centrifugation at 24,000 g, while macronuclear fragments sediment. After several cycles of centrifugation in Percoll, the micronuclei, although heavily contaminated with cytoplasmic components, are essentially free of macronuclei and macronuclear fragments. Micronuclear DNA can then be extracted from the suspension. The whole procedure is very rapid and in about an hour micronuclear and macronuclear DNA can be separated. About 2 micrograms of micronuclear DNA can be obtained from 6 x 10(7) paramecia. We find that there are internal sequences in the micronuclear A gene DNA in wild type cells which are eliminated when the micronuclei develop into macronuclei. They yield unique restriction fragments for micronuclei and macronuclei. Therefore the purity of the preparations is easily monitored by probing Southern blots of restriction enzyme-digested DNA with the cloned A gene. No differences have been found between the micronuclear A gene in wild type and the d48 mutant.  相似文献   

20.
Ciliates exhibit nuclear dimorphism, i.e. they have a germline micronucleus and a somatic macronucleus. Macronuclei are differentiated from mitotic sisters of micronuclei. The macronuclei of "higher ciliates" are polyploid and divide acentromerically ("amitotically"); they differentiate once per life cycle. By contrast, Karyorelict (KR) ciliate macronuclei are nearly diploid and cannot divide; they must differentiate at every cell cycle. Diverse lines of evidence are presented to support the hypothesis that ancestral ciliate macronuclei were incapable of division (as in living karyorelict ciliates) and that higher ciliates gained, perhaps independently more than once, the ability to divide the macronucleus. Selective pressures that could have driven the evolution and macronuclear division and two plausible step-wise pathways for the evolution of macronuclear division are proposed. These hypotheses are relevant to our understanding of amitosis mechanisms, evolution of nuclear dimorphism, and phylogenetic classification of ciliates.  相似文献   

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