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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular medicine 69 (1991), S. 567-575 
    ISSN: 1432-1440
    Keywords: Erythropoietin ; Kidney ; Anemia ; Oxygen ; Proximal tubule ; Endothelium ; Fibroblasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The kidney is the main site of erythropoietin (EPO) formation. Oxygen sensing in the kidney itself plays a major role in the control of EPO synthesis. By in situ hybridization it has been established that the EPO-producing cells are situated in the interstitium of the cortical labyrinth, but they have not been precisely identified. Morphological findings provide new insights into the location and mechanism of oxygen sensing in the kidney. In addition to causing an increase in the number of cells containing EPO messenger RNA, anemia provokes structural changes exclusively in the cortical labyrinth. Specifically, the fibroblasts become enlarged and show increased activity of 5′-nucleotidase, and the S1 segment of the proximal tubule shows similar alterations as in various models of hypoxia. Thus, structures that are situated in the close vicinity of the EPO-producing cells appear to be sensitive to decreased oxygen delivery.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Allogromia ; Helical filaments ; Microtubules ; Paracrystals ; Reticulopods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Allogromia sp. is a benthic foraminiferan protozoan which extends and withdraws a dynamic network of branching and anastomosing pseudopodia,i.e., reticulopods. Each reticulopod contains an elongate cytoskeleton composed primarily of microtubules (MT). When withdrawal was induced with artificial seawater supplemented with MgCl2, we found a time-dependent decrease in the number of reticulopodial MTs and a concomitant increase in 5-nm-diameter helical filaments. During the initial stages of withdrawal these helical filaments associated laterally to form loose aggregates. Later they formed dense paracrystalline aggregates, which appeared similar to those seen in the cell bodies of untreatedAllogromia juveniles prior to network extension. Similar results were obtained when withdrawal was induced by using seawater supplemented with other salts (NaCl, KCl). Treatment with an isotonic seawater substitute with an altered Na+:K+ ratio induced a momentary withdrawal, after which the organism recovered and reextended a network. During the withdrawal phase of this response, MTs became less abundant and aggregates of helical filaments more conspicuous. Together with earlier observations these findings suggest that helical filaments and paracrystalline material are an alternative or intermediate assembly form of MT proteins.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 249 (1987), S. 69-77 
    ISSN: 1432-0878
    Keywords: Primitive erythrocytes ; Cytoskeleton ; Microtubules ; Actin ; Spectrin ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cytoskeletons of primitive erythrocytes have been isolated from the embryos of day 12 pregnant C57/Bl mice and examined by transmission electron microscopy, immunofluorescence microscopy, and SDS-polyacrylamide gel electrophoresis. Microtubules are the most prominent cytoskeletal component. They are found either singly or organized into loose bundles just under the plasma membrane, but do not form classical marginal bands in most cells. Immunofluorescence with a polyclonal tubulin antiserum confirms this distribution and further reveals numerous mitotic figures among the cells. Rhodamine-conjugated phalloidin and heavy meromyosin labeling reveal that actin is localized in the cortex of the primitive erythrocyte in the form of 6 nm filaments. Antibody directed against avian erythrocyte alpha spectrin demonstrates that spectrin is also found in the cortex. Occasional 10-nm intermediate filaments, observed in the primitve erythrocytes by electron microscopy, are believed to be of the vimentin class based on positive reaction of the cells with vimentin-specific antiserum. In addition, a band in erythrocyte cytoskeletons comigrates in SDS-polyacrylamide gels with vimentin isolated from mouse kidney. Spectrin and actin were also found to be associated with the membrane of primitive erythrocytes when membrane ghost preparations were analyzed by SDS-polyacrylamide gel electrophoresis.
    Type of Medium: Electronic Resource
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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: To facilitate the direct study of the molecular events that control the development of human burst-forming units-erythroid (BFU-E), we have developed a method to purify BFU-E from peripheral blood. Using density centrifugation, rosetting with a mixture of neuraminidase-treated and IgG-coated sheep erythrocytes, positive panning with anti-My10 monoclonal antibody, overnight adherence to plastic dishes, negative panning with monoclonal antibodies, and density centrifugation, human blood BFU-E were purified from 0.04% to 56.6%, a 1,400-fold purification with a 13% yield. More than 90% of purified BFU-E were recombinant interleukin-3 (rlL-3) dependent, which survived for 48 h with rlL-3 in the absence of recombinant erythropoietin (rEP), and 80% gave rise to erythroid bursts of more than 500 hemoglobinized cells. rEP dependency was not evident until after 72 h of incubation in vitro. The purified cells (day 1) were incubated with rlL-3 and rEP in liquid culture for 24 (day 2), 48 (day 3), and 72 (day 4) h and then were transferred into semisolid cultures and incubated until day 15. The size of the erythroid colonies observed in semisolid cultures decreased continuously in association with the incubation time of day 1 purified cells in liquid cultures. The first appearance of colony-forming units-erythoid (CFU-E) that gave rise to colonies of 8 to 49 cells was observed after 72 h of incubation of day 1 cells in the liquid culture. 125I-rEP was incubated for 5 h at 37°C with purified cells (day 1) or with the cells that had been incubated in liquid culture for an additional 24-72 h, and the presence of erythropoietin (EP) receptors was investigated using auto-radiography. Specific binding of 125I-rEP was detected in 19 ± 7% of the initial day 1 BFU-E. The percentage of 125I-rEP-binding to erythroid progenitor cells and the amount of binding continuously increased as day 1 BFU-E matured. 125I-rEP specific binding was observed with all of the erythroid progenitor cells that had been incubated in liquid culture for 72 h. These data demonstrate that primitive BFU-E have a much lower number of EP receptors than CFU-E and develop an increased concentration of EP receptors in association with their maturation and loss of proliferative capacity.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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