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  • 1
    Unknown
    Stuttgart ; New York : G. Fischer
    Call number: QP501Z:5/14,4
    Keywords: Cell Communication ; Cell Division ; Cell Separation / methods ; Flow Cytometry / methods ; Kinetics
    Pages: vi, 65 p. : ill.
    ISBN: 3437108174
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    QP501Z:5/14,4 available
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 136 (1988), S. 194-197 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: When quiescent cells in monolayer culture are stimulated to proliferate with growth factor, the entry into S-phase or mitosis appears to follow first-order kinetics, with a probability to enter the cell cycle that depends on growth factor concentration (Smith and Martin, 1973). Suboptimal growth factor concentrations also lead to a decreased fraction of the cell population that responds to the stimulation (Brooks et al., 1984). Using flow cytometry, we have re-investigated this dual effect of growth factor concentration on cultures of quiescent normal human skin fibroblasts, stimulated with submaximal concentrations of fetal calf serum, epidermal growth factor, and platelet-derived growth factor. The size of the responding population decreased with decreasing concentration of growth factor, but the time course of cell division within this responding population was identical for all growth factor concentrations. This is in conflict with previous concepts and indicates that the entry into the proliferative state is based on a decision mechanism that cannot be adequately described using transition probabilities determined by mitogen concentration.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The growth, in vitro of the murine myeloid cell line FDC-P1 depends on the presenc of serum and a murine hemopoietic growth factor (either granulocyte/ macrophage colony-stimulating factor (GM-CSF) or multipotential colony-stimu-lating factor (multi-CSF, IL3)). To determine the differential roles of serum and colony-stimulating factor (CSF) during the growth of FDC-P1 cultures, we investigated the kinetics of proliferation and death after withdrawal of serum or CSF, using flow cytometry to quantitate the numbers of vital and dead cells. After withdrawal of CSF, the cells died without entering a quiescent state. The life span of cultures lacking CSF increased with increasing concentrations of serum (〉 50 h at 30% serum), and the cells kept dividing until they died. During the period of population death caused by the absence of CSF, the re-addition of CSF immediately prevented further cells from dying. After the withdrawal of serum in the presence of CSF, the cells continued to live and proliferate for weeks, but required high cell densities (〉〉 105/ml), which suggests that the cells produced an active substance that can substitute for serum. Serum as well as serum-free conditioned medium from dense cultures made the survival and growth of FDC-P1 cultures independent of cell density. Without sufficient quantities of this activity, all cells of the population died within an interval that was much shorter than one cell cycle, which indicates that the factor acts throughout most of the cell cycle. The results suggest that both the CSF and the serum factor act together to permit cell survival, rather than to drive proliferation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 155 (1993), S. 79-88 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cell density negative control (CDNC) of normal human fibroblast proliferation occurs after stimulation by mitogens with different signal transduction mechanism. Delayed exposure to agents that interfere with CDNC, such as doublestranded RNA and vanadate, reveals the existence of a biochemical event, involved in CDNC, that occurs 5-8 hr after the beginning of mitogenic stimulation. This is earlier than the point of “mitogenic commitment,” defined by the duration of mitogen exposure required for cell cycle entry (8-18 hr). Phosphorylation of the retinoblastoma gene product (pRB) begins 8-10 hr after mitogen stimulation and is nearly complete at 18 hr, just as the first cells enter S-phase. CDNC prevents pRB phosphorylation. Interferon β delays pRB phosphorylation by up to 20 hr but has little effect on the timing of mitogenic commitment. Thus mitogenic commitment is located in time between CDNC and pRB phosphorylation. When agents that cause a release from CDNC are applied to dense, negatively controlled cultures after 18 hr of EGF stimulation, pRB phosporylation occurs 6-8 hr after release. This suggests that the negatively controlled cells process the mitogenic signal but accumulate at a restriction point. The relatively early timing of CDNC-related events in the prereplicative phase raises the possibility that pRB phosphorylation is a consequence rather than a prerequisite for release from cell density negative control. © 1993 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: When quiescent normal skin fibroblasts are stimulated by mitogens such as epidermal growth factor (EGF), the proportion of cells entering a division cycle decreases with increasing cell density. The presence of a synthetic double-stranded RNA (poly I:C) enhances this density-related restriction. Fetal calf serum (FCS) as well as human serum (HS) and human platelet-poor plasma (HPPP) completely abrogate the inhibiting effect of cell density on EGF mitogenicity, both in the presence and absence of poly I:C. HS and HPPP are up to ten times more potent than FCS in overcoming density-related restriction of EGF mitogenicity in human skin fibroblasts, whereas the mitogenic potencies of FCS, HS and HPPP in the absence of EGF are identical. Thus the mitogenic activity of FCS, HS and HPPP and their ability to overcome the density-related restriction of EGF-induced proliferation may be due to different molecules. Addition of FCS or HS at various times after EGF exposure reveals two distinct control points within the prerepli-cative phase: one within the first 2 hours and the other between 10 and 20 hours after the beginning of EGF exposure. Thus, the interactions of EGF, serum, and poly I:C reveal the kinetics of a cell density-related mechanism of negative proliferation control.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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