摘要:

High‐resolution scanning electron microscopy (SEM) has previously been used to study intracellular detail, including chromatin. It has, however, been commonly carried out either on cellular subfractions or following extraction methods to visualize detail. In the work presented here, intracellular detail of neurons of the dorsal root was visualizedin situby viewing freeze‐fracture faces obtained after hypotonic expansion. This procedure permits the detailed resolution, by SEM, of juxtanuclear and intranuclear detail to a degree impossible without hypotonic dispersal. In agreement with work previously reported, nuclear chromatin of these interphase cells presents largely as 30‐nm fibers, with a next higher hierarchical structure imparted by swelling in magnesium chloride. Detailed analyses showed that particles as small as 10‐nm nucleosomes comprising the 30‐nm chromatin fiber could be resolved, with ≪end‐on≫ views of such fibers showing 5 nucleosomes per helical turn of the fiber. Chromatin fibers positioned subjacent to nuclear pores, or associated with ≪ nuclear spaces ≫ communicating with nuclear pores, were frequently found to be resolved as clusters, in an apparently more decondensed conformation, rather than tightly coiled into the 30‐nm fiber. In addition, details of the nuclear envelope, including nuclear pores and perinuclear filaments as well as membranes of the endoplasmic reticulum, decorated with ribosomes,

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00735.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Assembly of active nuclei in lymphocytes stimulated by mitogen is paralleled by the elaboration of a structurally and biochemically complex nuclear matrix (NM). To examine the dynamics of individual NM polypeptide components during blastogenesis, we have applied immunofluorescence labelling with anti‐NM antibodies to concanavalin A‐stimulated mouse splenocytes. Whereas peripherin and PI2 antigens did not reorganize during stimulation, labelling of PI1 and small nuclear ribonucleoprotein (snRNP) antigens increased markedly in intensity and redistributed in concert with the previously reported NM restructuring. Double‐labelling showed, furthermore, that snRNPs and the internal staining component of P11 were largely co‐localized. As an approach to studying the role of RNA and RNA synthesis in NM organization, we have further examined the effects of the inhibitor of RNA synthesis, 5,6‐dichloro‐1‐β‐d‐ribofuranosyl benzimidazole (DRB), on NM antigen distribution. The rapid inhibition of3H‐uridine incorporation by DRB was accompanied by coordinate aggregation of snRNPs and of the internal PI1 component into large, brightly stained patches. Both3H‐uridine incorporation levels and antigen localization were readily reversed upon removal of DRB. We conclude that NM antigens behave independently during nuclear and NM assembly and that NM organization, as reflected by NM antigen distribution, is modulated by con A‐ and DRB‐induced alterations in RNA synthesis. We propose, furthermore, that the PI1 antigen plays a role in RNA metabolism, and is possibly involved in RNA transpor

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00736.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The nucleolus‐associated chromatin (NAC) became argyrophilic when the root tips ofVicia fabawere treated with 0.2 μg/ml actinomycin D (AMD) for 15 hr at 22°C. To determine how the argyrophilic NAC is formed, detailed observations were carried out on thin sections following silver staining and ribonucleoprotein (RNP) preferential staining. In a few instances, thick channels with loosely packed fibrillar material (light fibrillar area) were seen meandering throughout the nucleoli. Large granules 280–330 Å in diameter (300 Å granules), which responded positively to both RNP preferential staining and silver staining, were sometimes present within the light fibrillar area. Some fragments of NAC were also seen in the light fibrillar area and, interestingly, they responded positively to silver even though they were bleached by the RNP preferential staining. Most nucleoli showed a segregation of two major components, the fibrillar and granular components. The nucleolar vacuoles were localized strictly within the fibrillar component and usually accompanied the light fibrillar area or, alternatively, contained a number of 300 Å granules. Another category was characterized by the presence of poorly developed vacuoles in which the 300 Å granules were still found, and the spherical argyrophilic NAC associated with the surface of the nucleolus. The present observations suggest that AMD induces the DNA‐containing structure engaged in ribosomal RNA transcription to condense, and during this process some argyrophilic proteins are incorporated into the chromosomal structure thereby causing the NAC to become argyrophilic. In this context, the NAC is assumed to contain ribosoma

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00737.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The distribution of DNA in Ehrlich tumour cell nucleoli was investigated by means of an immunocytochemical approach involving a monoclonal antibody directed against double‐ and single‐stranded DNA. Immunolabelling was performed either before or after the embedding process. The postembedding labelling method allows better ultrastructural preservation than the preembedding labelling method. In particular, the various nucleolar components are well preserved and identifiable. In the nucleolus, labelling is particularly concentrated over the perinucleolar chromatin and over its intranucleolar invaginations, which penetrate the nucleolar body and often terminate at the fibrillar centres. In addition, aggregates of gold particles are found in the fibrillar centres, preferentially towards the peripheral regions. By contrast, the dense fibrillar component is completely devoid of labelling. The result seem to indicate that DNA containing the rDNA genes is located in the fibrillar centres, with a preference for the peripheral regions. This finding suggests that transcription of the rDNA genes should occur within the confines of the fibrillar centre, probably close to the boundary region of the surrounding dense fibrillar component. The results are discussed in the light of present knowledge of the functional organization of the nucleo

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00738.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The development of a single, very large (25–35 μm diameter) nucleolus during oogenesis in the crustaceanAcanthocyclops vernalisis described. The nucleolus is the site of ribosomal RNA production the egg, as shown byin situhybridization, and apparently the only source, as accessory cells are not observed. Ribosomal DNA amplification, as manifested by the presence of multiple nucleoli, is also not observed. Silver staining and C‐banding suggest that chromosomal regions other than the nucleolar organizer are involved with the elaboration of the nucleolus. These observations, along with what is known about the nature of the DNA lost during the developmental process of chromatin diminution in this organism, suggest a relationship between the large oocyte nucleolus and the DNA lost during diminu

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00739.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The HT29 cell line, derived from a human colon adenocarcinoma, is able to differentiate if galactose replaces glucose in the culture medium. We have isolated a clone (HT29‐18) from this cell which displays differentiated properties of the parent cell line. HT29‐18 cells grown in glucose‐containing medium form multiple layers of round cells without specific cell‐cell adhesion. In contrast, when grown in galactose‐containing medium, they form a monolayer with tight junctions and exhibit a well differentiated brush border at their apical membrane, which faces the culture medium. The polarized properties of HT29‐18 cells grown galactose‐containing medium were demonstrated by immunofluorescent techniques with antibodies against 2 plasma membrane proteins. Class I histocompatibility antigens (HLA) and transferrin receptors, 2 well characterized integral membrane proteins, are uniformly distributed on the cell surface of undifferentiated HT29‐18 cells, but acquire a polarized distribution during differentiation, localized on the basolateral membranes and absent from the apical surface. Binding of125I‐labeled transferrin was used to determine transferrin receptor distribution on apical and basolateral membranes. Functional tight junctions in the differentiated cultures were demonstrated, as the monolayer was impermeable to a permeation dye (ruthenium red) as well as to antibodies. The sealing of these tight junctions is, asin vivo, Ca++‐dependent as they could be opened by a short incubation

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00740.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The acetylcholine receptor (AChR) synthesis, insertion and degradation rates are regulated by numerous intracellular and extracellular agents. Recent studies have shown that Ca2+and Ca2+ionophores have a profound regulatory effect on the appearance of AChR clusters and AChR synthesis [3, 15, 23]. These regulatory effects may be mediated through the activation of calcium and phospholipid‐dependent protein kinases by agents such as phorbol esters. In this study, we have utilized 4‐β‐phorbol‐12‐myristate‐13‐acetate (PMA) in order to determine whether the activation of protein kinase C exerts a regulatory effect on the expression of AChRs in cultured chick myotubes. Our results show that 4‐β‐phorbol‐12‐myristate‐13‐acetate decreased intracellular AChRs and suppressed AChR synthesis without affecting the turnover rate. Control and PMA treated cells labeled with [35S] methionine and immunoprecipitated with a monoclonal antibody to the α subunit of AChRs (mAb35) revealed a significant decrease in radioactivity precipitated after exposure to PMA. Polyacrylamide gel electrophoresis revealed no major changes in protein patterns, or in newly synthesized proteins as determined by [35S] methionine incorporation and autoradiography. Other enzymes important in muscle metabolism were not affected by PMA treatment. Our results indicate that activation of protein kinase C results in the suppression of AChRs synthesis an

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00741.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Calbindin‐D28Kwas immunohistochemically localized in myenteric and submucosal plexuses throughout the rat intestine. Calbindin‐D28Kimmunoreactivity was found in about half of myenteric neurons and in more than 90% of submucosal neurons. Calbindin‐D28Kwas also observed in nerve processes running inside ganglia, muscle layers and lamina propria. No correlation could be established between the presence of calbindin‐D28Kand the distribution of neuropeptides localized in this study (VIP, enkephalin, somatostatin and substance P). In addition, some endocrine‐like cells of the ileum were calbindin‐D28K‐positive. Half of these endocrine cells also contained neurotensin but none of the other neuropeptides

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00742.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Beryllium absorption sites in the kidney and liver of rats have been located and imaged at approximately 70 nm lateral resolution with a scanning ion microprobe utilizing secondary ion mass spectrometry. Embedded sections and lyophilized cryosections of these organs were prepared afterin vivoadministration of beryllium in soluble form. Beryllium distribution images were correlated with the histological microstructure revealed by CN−images. In the kidney, beryllium concentrates selectively within the nuclei of proximal tubule cells and occasionally within modified podocytes or mesangial cells in the glomerulus. In the liver, beryllium is seen to localize within severely altered lysosomal structures as well as within hepatocyte nuclei. These observations are relevant to understanding aspects of the toxic and carcinogenic properties of absorbed beryllium compound

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00743.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The anionic sites of the basement membrane of rat seminiferous tubules were demonstrated ultrastructurally in the lamina densa by using cationic polyethyleneimine (PEI). The sites were largely digested out after incubation with heparitinase, indicating a large proportion of heparan sulfates. The anionic sites were present as early as day 16 of gestation on the interstitial side of the lamina densa, and after gestation day 20 they were symmetrically organized on both sides of the lamina densa. The number of sites is not modified postnatally. They appear more irregular in density with advancing age. Experimental conditions as crytorchidism, fetal irradiation, and ligation of the ductuli efferentes lead to unspecific alterations in the distribution of the anionic sites that are parallel to the modifications in the basement membrane.

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00744.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY