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Long-term culture of bone marrow derived stromal colony forming cells (S-CFC) in matrix and nutrient defined agar medium resulted in stromal cell colonies that pass sequentially through three distinct morphological stages: firstly, aggregated loose syncytium of round to ovoid cells (stage I), a second developmental stage of large branching colonies in which the cells become enlarged, elongated with cytoplasmic projections forming a loosely anastomized network with adjacent cells (stage II), and finally cells become dissociated, loosing their long, thin cytoplasmic filaments and breaking their contacts with one another, but remain large and retain a bi-polar nature (stage III). Cells were also grown in liquid medium in a culture microenvironment closely resembling conditions of haemopoiesis in vitro. Using a panel of well defined monoclonal antibodies reactive against the rat, rabbit and human growth hormone receptors, this study found immunochemical evidence of the presence and localization of binding sites of growth hormone (GH) in the cell membrane and extra-nuclear Golgi area of long-term bone marrow derived human stromal cells in liquid and semi-solid nutrient agar mediums. GH-receptor immunoreactivity was present in small proliferating progenitor cells, myofibroblast-like cells, large reticular fibroblast cells, adipocytes and endothelial cells. Only MAb known to be reactive against human tissue resulted in strong immunoreactivity. The expression of GH-receptors not only on small proliferating, but also on the well differentiated cells, indicates a role for growth hormone on non-progenitor cells. GH-receptor immunoreactivity on differentiating and/or differentiated cells suggests that GH is also necessary for, or has a trophic function in differentiation. We propose that direct GH action is necessary not only for differentiation of progenitor cells as implied by the dual effector hypothesis, but also their subsequent clonal expansion, differentiation and maintenance.  相似文献   
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Results of field experiments with soil compaction induced by wheel traffic applied uniformly to cover the entire surface of the experimental plots are reported. Compaction was done immediately before sowing, and each year, in each location, the same treatments were repeated on the same plots. The number of tractor passes varied between 0 and 30. The experiments were conducted during the 1978–1981 period in four locations with different soil and climatic conditions.Changes in soil physical properties, as well as in the yield of maize grain, were shown to be related to the number of tractor passes according to regression formulae of the type: Y = aXb. Most of the changes were recorded between 0 and 8–10 passes, while with more than 15–20 passes changes became negligible. The average maximum increase in bulk density was 20–25% as compared with the non-compacted control plot, and the average maximum decrease in yield was 46%. Moisture content in the compacted control plot, and the was 2–3% (w/w) lower than in the control plot, except for the soils with poor drainage where the lower part of the compacted topsoil showed an increase in moisture content. Air content in the compacted plots often dropped below 10, and occasionally to nearly 0% (v/v). For three of the four locations, grain yield of maize linearly decreased by 13 kg ha?1 (or 0.18% of the control plot yield) for each 1 kg m?3 increase in bulk density.  相似文献   
4.
We generated mice lacking Cks2, one of two mammalian homologs of the yeast Cdk1-binding proteins, Suc1 and Cks1, and found them to be viable but sterile in both sexes. Sterility is due to failure of both male and female germ cells to progress past the first meiotic metaphase. The chromosomal events up through the end of prophase I are normal in both CKS2-/- males and females, suggesting that the phenotype is due directly to failure to enter anaphase and not a consequence of a checkpoint-mediated metaphase I arrest.  相似文献   
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Acting as a signal, hydrogen peroxide circumvents antioxidant defense by overoxidizing peroxiredoxins (Prxs), the enzymes that metabolize peroxides. We show that sestrins, a family of proteins whose expression is modulated by p53, are required for regeneration of Prxs containing Cys-SO(2)H, thus reestablishing the antioxidant firewall. Sestrins contain a predicted redox-active domain homologous to AhpD, the enzyme catalyzing the reduction of a bacterial Prx, AhpC. Purified Hi95 (sestrin 2) protein supports adenosine triphosphate-dependent reduction of overoxidized PrxI in vitro, indicating that unlike AhpD, which is a disulfide reductase, sestrins are cysteine sulfinyl reductases. As modulators of peroxide signaling and antioxidant defense, sestrins constitute potential therapeutic targets.  相似文献   
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We can no longer afford to ignore the serious potential consequences of our lavish use of energy. Continuation of the present rate of increase, particularly with the trend to imported fuels, will lead in short order to a level of dependency on imports which is disturbing for both the national security and the balance of payments. The inevitable rise in the price of energy will presumably lead to some increases in the domestic energy supply. But our reserves, particularly in the preferred forms of petroleum, gas, and even low-sulfur coal, are finite. Thus, the energy problem must also be attacked from the standpoint of energy conservation. The forthcoming rise in fuel prices will, of course, make more attractive some forms of conservation which at present are economically marginal. Nevertheless, consumers, industry, and government will have to make difficult choices in the years ahead: between greater convenience and lower energy bills, between the high capital costs of energy conservation measures and the long-term dollar savings from increased energy efficiency, and between environmental protection and the availability of needed energy supplies. Existing capabilities and technology, on which short- and midterm improvements must be based, appear to offer substantial possibilities for reducing U.S. energy consumption within the next decade (11). Long-term solutions to the energy problem, however, will depend to a considerable extent on the continuing appearance of new technological capabilities for increased efficiency of energy utilization and increased integration of energy applications. The capacity for continuing technological advances is, of course, dependent in turn on a strong relevant scientific base. A word of caution is necessary. Recent experience has shown that technological advances alone will not solve the problem. The problem spans not only the traditional physical and engineering sciences but also those sciences which deal with human attitudes and actions, that is, the social sciences, and includes a more fundamental understanding of underlying economic principles. The challenge to all sectors of American science should be clear.  相似文献   
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Soil macroinvertebrates were studied in a Mediterranean-type forest on brown-pebble forest soils in southern Russia. At the site, 144 intact soil cores (76 cm2 each) forming a grid of 24 × 6 units were taken in order to determine animal spatial distribution. Abundance of isopods was 166.3 ± 16.0 indiv. m–2 and they constituted about 12% of the total macrofaunal abundance. Biomass of isopods was 3.5 g m–2, or about 21% of the total biomass of macrofauna. Three woodlice genera (Armadillidium, Cylisticus, and Trachelipus) were found at the site. The two latter genera formed almost all (93%) of the isopod population. We found that spatial distribution of woodlice was heterogeneous: areas with 4–5 individuals per sample were neighboring those without animals. In order to study soil factors influencing isopod distribution in the brown-pebble forest soil, the size of a sample was artificially increased by combining adjacent sample units. Litter mass (r = 0.41) and loss on ignition (LOI) (r = –0.55) significantly influenced isopod distribution. Soil pH was near neutral (6.79), LOI was 8.39, and the water holding capacity was 70.9%. Pebbles comprised up to 84% of the sample's mass. Ca. 40 samples are recommended for estimation of isopod abundance in brown forest soil.  相似文献   
10.
Sentinel steers were placed with 3 beef herds on irrigated pastures in southern Idaho for 1-month periods from May until November 1982 to determine the transmission pattern of Fasciola hepatica. Transmission was found to increase through the pasture season, reaching a peak during November. Overwintering of metacercariae or snail-borne stages was not found to contribute to infections in the year under study. A variety of species of Lymnaea were found to be available in southern Idaho as potential intermediate hosts. The enzyme-linked immunosorbent assay was found to be a good serologic indicator of light infections with F hepatica. The serum gamma-glutamyltransferase activity was not diagnostically significant when the degree of fluke infection was low.  相似文献   
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