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  • 1
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A time course study of the sequential appearance of erythropoietin-dependent colonies and bursts (derived from CFU-E and BFU-E, respectively) was performed on mouse hemopoietic cells cultured in methyl cellulose containing 2-mercaptoethanol. A new type of small, short-lived burst was found to be apparent by the third day in culture. By the sixth day most of these bursts had lysed. At the same time, differentiating erythroblasts began to be detectable in the large, late appearing bursts described previously.These two types of burst, differing from each other and from CFU-E derived colonies both in their ultimate size and morphology, as well as in their time course of appearance and lysis, were compared in other ways. It was found that early burst formation required about 100 times more erythropoietin than that needed to stimulate CFU-E. On the other hand, early burst formation required less than one-quarter of the amount of erythropoietin needed to obtain the large, late appearing bursts. Comparison of the distribution of early burst progenitors relative to pluripotent stem cells (CFU-S) in individual spleen colonies gave a correlation coefficient that was also intermediate between that obtained comparing CFU-S with CFU-E and that obtained comparing CFU-S with the progenitors of late bursts. These results suggest that decreasing proliferative capacity is associated with progressively increasing erythropoietin responsiveness as primitive erythropoietic progenitors move from a position close to pluripotent stem cells through several differentiation steps to reach a stage just prior to the onset of detectable hemoglobin synthesis.
    Additional Material: 7 Ill.
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  • 2
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The laminin A chain has been sequenced by cDNA cloning and was found to contain an RGD sequence. Synthetic peptides containing the RGD sequence and flanking amino acids were active in mediating cell adhesion, spreading, migration, and neurite outgrowth. Furthermore, endothelial cell attachment to a laminin substrate was inhibited by an RGD-containing synthetic peptide. Antisera against the integrin (fibronectin) receptor, and monoclonal antibody to the integrin, VLA-6, inhibited cell interaction with laminin, as well as with peptides containing an RGD sequence. These results suggest that the RGD containing site of laminin is active and interacts with the integrin family of receptors in certain cells.
    Additional Material: 7 Ill.
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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: Changes in the number and erythropoietin sensitivity of erythropoietic progenitor cells (CFU-E or E) capable of erythropoietin-dependent colony formation in culture have been measured in mice subjected to a variety of manipulations known to affect erythropoiesis. Injection of erythropoietin into mice whose E levels had been reduced by transfusion-induced plethora stimulated a striking increase in this population within 24 hours in both spleen and marrow. Following irradiation and marrow transplantation E were found to regenerate in the spleen with a population doubling time of 6 hours. Evidence of erythropoietin-dependent stimulation of E in vivo under conditions of hemopoietic regeneration was also obtained, although substantial numbers of E were detected in both regenerating spleen and marrow of plethoric mice even without erythropoietin administration, In the same experiments comparable effects of erythropoietin on pluripotent stem cells or the progenitors of granulopoietic colonies in culture were not observed. Detailed studies of the dependence of colony formation on erythropoietin concentration in culture showed variations in erythropoietin sensitivity of E from normal, regenerating and plethoric, erythropoietin-stim-ulated spleen and marrow. This finding provides the basis for an extremely fine mechanism regulating the flow of erythropoietic differentiation at the level of the production of E.The number of E present in the marrow of untreated W/WV mice was normal, but their sensitivity to erythropoietin in culture was decreased to a similar extent as E from normal mice exposed to a heightened erythropoietic demand. Plethora had a more marked effect in reducing E numbers in W/WV mice than in +/ + controls and stimulation of E following subsequent erythropoietin administration was highly defective. The results of these studies provide further evidence that cells identified as E represent a stage of differentiation along the erythropoietic pathway that is several steps removed from pluripotent stem cells and support the view that erythropoiesis, granulopoiesis and stem cell self-renewal are regulated to a major degree by independent mechanisms.
    Additional Material: 8 Ill.
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  • 4
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Properties of the cells (TE-CFU) that give rise within four to six days to transient endogenous erythropoietic spleen colonies in irradiated mice have been investigated. The results obtained indicate that (1) erythropoietic maturation within such colonies is highly erythropoietin-dependent, (2) the population size of TE-CFU is not erythropoietin-dependent, (3) initial exposure to a high dose of erythropoietin followed by continuing exposure to lower doses is required for maximal efficiency of colony formation by TE-CFU, (4) successful transplantation of TE-CFU has not been achieved, but they appear among the progeny of transplanted hemopoietic cells, (5) TE-CFU are defective in mice of genotype W/Wv. These findings are consistent with the view that the TE-CFU assay detects a class of early erythropoietin-sensitive progenitor cells committed to erythropoietic differentiation, rather than “abortive” colony formation by pluripotent stem cells.
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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: The differentiated state of mouse erythropoietic progenitor cells (CFU-E), detected by their ability to form erythropoietin-dependent colonies in vitro, has been investigated. Transfusion-induced plethora was found to reduce the population size of CFU-E in both spleen and femoral marrow, which indicates that a significant number of CFU-E arise by differentiation processes that are themselves erythropoietin-dependent. Individual spleen colonies were found to be heterogeneous in their content of CFU-E, and the numbers of CFU-E per colony were not correlated either positively or negatively with the numbers of granulocyte-macrophage progenitors (CFU-C) present in the same colonies. The absence of a negative correlation between CFU-E and CFU-C indicates that the erythropoietic and granulopoietic pathways of differentiation are not mutually exclusive within individual spleen colonies. The numbers of CFU-E per spleen colony were also found to vary independently of the numbers of pluripotent stem cells (CFU-S) per colony; in contrast, as found previously, the numbers of CFU-C and CFU-S per colony were positively correlated. These results indicate that more randomizing events separate CFU-E from CFU-S than separate CFU-C from CFU-S, and are consistent with the view that CFU-E occupy a position on the erythropoietic pathway of differentiation that is more remote from the pluripotent stem cells than is the corresponding position of CFU-C on the granulopoietic pathway.
    Additional Material: 5 Ill.
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