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  • Electronic Resource  (2)
  • Antigenic variation  (1)
  • Bone marrow transplantation  (1)
  • 1
    ISSN: 1619-0904
    Keywords: In vivo tissue engineering ; Bone marrow transplantation ; bFGF ; Release system of angiogenic growth factors ; Revascularization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract For successful in vivo tissue engineering, a growth factor release system will be useful. We adopted autologous bone marrow transplantation as an angiogenic growth factor release system. Bone marrow transplanted into a synthetic vascular prosthesis produced continuous synthesis of angiogenic growth factors, resulting in rapid neointima formation on the prosthesis after implantation. We expected a similar angiogenic phenomenon to occur if bone marrow was transplanted into ischemic myocardium. Bone marrow was transplanted into ischemic myocardium created in dogs. Marrow cells continued synthesis of angiogenic growth factors, which were effective in protecting the capillary network from ischemia, but not myocytes. Autologous bone marrow was injected intramuscularly into ischemic myocardium created in the left ventricular wall of dogs. Control operations were performed without bone marrow. On days 3 and 7, marrow cells survived, and their adjacent cells and the surrounding extracellular matrix were immunohistochemically bFGF reactive. At 3 weeks, no marrow cells were identified. Myocytes disappeared, but the capillary blood vessel networks remained. With some exceptions, these capillaries did not contain blood cell components. In the controls, scar tissue with a very small number of capillaries was formed. In conclusion, marrow cells survived for a short period of time after transplantation, and continued synthesis of angiogenic growth factors, which were effective in protecting endothelial cells from ischemia, but not myocytes. Therefore, the results also suggest that there are limitations in the treatment of ischemic myocardium using angiogenic growth factors alone.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Homologous recombination ; Plasmid linear multimer ; Yeast mating-type switching ; Antigenic variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Gene conversion - apparently non-reciprocal transfer of sequence information between homologous DNA sequences - has been reported in various organisms. Frequent association of gene conversion with reciprocal exchange (crossing-over) of the flanking sequences in meiosis has formed the basis of the current view that gene conversion reflects events at the site of interaction during homologous recombination. In order to analyze mechanisms of gene conversion and homologous recombination in an Escherichia coli strain with an active RecF pathway (recBC sbcBC), we first established in cells of this strain a plasmid carrying two mutant neo genes, each deleted for a different gene segment, in inverted orientation. We then selected kanamycin-resistant plasmids that had reconstituted an intact neo + gene by homologous recombination. We found that all the neo + plasmids from these clones belonged to the gene-conversion type in the sense that they carried one neo + gene and retained one of the mutant neo genes. This apparent gene conversion was, however, only very rarely accompanied by apparent crossing-over of the flanking sequences. This is in contrast to the case in a rec + strain. or in a strain with an active RecE pathway (recBC sbcA). Our further analyses, especially comparisons with apparent gene conversion in the rec + strain, led us to propose a mechanism for this biased gene conversion. This “successive half crossing-over model” proposes that the elementary recombinational process is half crossing;-over in the sense that it generates only one recombinant DNA duplex molecule, and leaves one or two free end(s), out of two parental DNA duplexes. The resulting free end is, the model assumes, recombinogenic and frequently engages in a second round of half crossing-over with the recombinant duplex. The products resulting from such interaction involving two molecules of the plasmid would be classified as belonging to the gene-conversion type without crossing-over. We constructed a dimeric molecule that mimics the intermediate form hypothesized in this model and introduced it into cells. Biased gene conversion products were obtained in this reconstruction experiment. The half crossing-over mechanism can also explain formation of huge linear multimers of bacterial plasmids, the nature of transcribable recombination products in bacterial conjugation, chromosomal gene conversion not accompanied by flanking exchange (like that in yeast mating-type switching), and antigenic variation in microorganisms.
    Type of Medium: Electronic Resource
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