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  • 1
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Ribosomal RNA (rRNA) genes in eucaryotes hold out the possibility of a temporal and spatial understanding of structural events in genetic regulation, since they are present in very large copy numbers and are extensively transcribed within a highly organised and specialised organelle-the nucleolus. However, although the existence of the genes within active nucleoli has been beyond dispute for many years, their position and arrangement has been the subject of considerable recent controversy. We have made use of the very sensitive and photometrically accurate imaging given by a cooled solid state CCD camera, coupled with computer deconvolution, to image DNA directly within nucleoli by three dimensional (3-D) optical microscopy. Our results show that DNA is more widely distributed than immunogold techniques have indicated and that in addition to brightly staining structures, corresponding to fibrillar centres, there is also a large amount of diffuse DNA, consistent with DNA location in other nucleolar components; this dispersed DNA is likely to correspond to the sites of gene transcription.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 249 (1987), S. 533-540 
    ISSN: 1432-0878
    Keywords: Apoptosis ; Necrosis ; Uterus ; Estrogen ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The luminal epithelium of adult ovariectomized mice responds to estradiol-17β with a synchronised wave of DNA synthesis and mitosis. Estriol, however, although producing a similar DNA-synthetic and mitotic response fails to cause an increase in cell number owing to a wave of cell death occurring at mitosis. In the present study it was shown that cells died by two different routes. The majority died by apoptosis but, unusually, a minority also died by necrosis. In the apoptotic cells the cytoplasm became dense, the endoplasmic reticulum and nuclear cisternae dilated; chromatin became marginated the nucleus shrank and became deeply infolded and contorted. Apoptosis, however, was uncharacteristic in that the nucleus failed to fragment, form caps or show disruption before the cells died by membrane rupture. Furthermore, the cells were frequently lost in sheets from the epithelium into the lumen. Part of the biochemical explanation for this onset of cell death comes from the accelerated loss from the tissue of estriol when compared to estradiol-17β. This resulted in a decline in protein and rRNA biosynthesis and a failure to complete ribosomal maturation. Evidence in favour of this explanation came from experiments that showed a return to the estradiol-17β level of response and an inhibition of cell death when the occupancy of the estriol receptor was maintained.
    Type of Medium: Electronic Resource
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