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  • Homologous recombination  (1)
  • Key words: Osteoclast — Monocyte — Macrophage — Differentiation — Bone Resorption.  (1)
  • MATERIALS  (1)
  • 1
    ISSN: 1432-0827
    Keywords: Key words: Osteoclast — Monocyte — Macrophage — Differentiation — Bone Resorption.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Mononuclear precursors of the human osteoclast have been identified in both bone marrow and the circulation in man, but osteoclast membership of the mononuclear phagocyte system (MPS) and its precise cellular ontogeny remain controversial. We isolated human hematopoietic marrow cells, blood monocytes, and peritoneal macrophages and incubated each of these cell populations with UMR106 osteoblast-like cells on glass coverslips and dentine slices in both the presence and absence of 1,25 dihydroxyvitamin D3 (1,25(OH)2D3), macrophage-colony stimulating factor (M-CSF), and dexamethasone. Cells isolated from peripheral blood and peritoneal dialysis fluid were positive only for monocyte/macrophage markers (CD11a, CD11b, CD14, and HLA-DR) and negative for osteoclast markers [tartrate-resistant acid phosphatase (TRAP), vitronectin reception (VNR), and calcitonin (CT) receptors and did not form resorption pits on dentine slices after 24 hours in culture. Similarly marrow cells did not form resorption pits on dentine slices after 24 hours in culture. However, after 14 days in co-culture with UMR106 cells, in the presence of 1,25(OH)2D3 and M-CSF, numerous TRAP, CT receptor, and VNR-positive multinucleated cells capable of extensive lacunar resorption were formed in co-cultures of all these preparations. The presence of 1,25 (OH)2D3, M-CSF, and UMR106 were absolute requirements for osteoclast differentiation. It is concluded that precursor cells capable of osteoclast differentiation are present in the marrow compartment, the monocyte fraction of peripheral blood, and in the macrophage compartment of extraskeletal tissues and that these cells are capable of differentiating into mature functional osteoclasts. These findings argue in favor of osteoclast membership of the human MPS.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Homologous recombination ; Protoplast transformation ; β-Glucuronidase ; Maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The requirements for homologous recombination between plasmid DNA molecules have been studied using the PEG (polyethylene glycol)-mediated transformation system of maize (Zea mays L.) protoplasts coupled with the transient expression assay for β-glucuronidase (GUS). Two plasmids were introduced into maize protoplasts; one plasmid (pB×26) contained a genomic clone of the Adh1 maize gene; the other plasmid (piGUS) was a promoterless construction containing part of intron A of the Adhl gene fused to the gusA coding sequence. Thus, the two vectors shared an effective homologous region consisting of a 459 by (Hindlll—PvuII) fragment of the yAdh1 intron A sequence. An active gusA fusion gene would result upon homologous recombination between the plasmids within the intron A sequence, and indeed GUS activity was observed in extracts following co-transformation of maize protoplasts with the two plasmids. The presence of recombinant DNA molecules in protoplast DNA isolated 1 day after co-transformation was verified using polymerase chain reactions (PCR) and Southern blots. For efficient homologous recombination, both plasmids had to be linearized. The recombination reaction was induced by restriction of the plasmid molecules either inside the effective homologous region or at the borders of the intron sequence. However, the presence of even small, terminal, nonhomologous sequences at the 3′ end of the pB×26 fragment inhibited the recombination reaction. Also, both ends of the linearized piGUS DNA molecules were involved in the recombination reaction. The results revealed some features of homologous recombination reactions occurring in plant cells which cannot be accommodated by mechanisms postulated for similar reactions in animal system and in lower eukaryotes.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2010-09-29
    Description: Data was obtained on silicone-bonded fiberglass, isocyanurate foam, and two dozen other insulators. Materials were selected to withstand heat sterilization, outer space, and the Martian atmosphere. Significant environmental parameters were vibration, landing shock, and launch venting.
    Keywords: MATERIALS
    Type: NPO-11586
    Format: application/pdf
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