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1.
WERNER A. MÜLLER 《Differentiation; research in biological diversity》1982,22(1-3):141-150
Several topics and concepts in developmental biology, such as induction of secondary axes (as in amphibians), the rules of distal transformation (valid, e.g., for insect and vertebrate limbs), and the rule one piece regenerates, the other one duplicates (valid also for imaginal discs) originally emerged from pioneering studies in hydroids. In addition, one finds phenomena of intercalation, i.e., the insertion of intervening parts when tissues of distant origin are confronted with each other. However, since not only short-range but also long-range interactions contribute to pattern regulation, one observes more regulative flexibility as compared to insect systems. 相似文献
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JOSÉ M. MATO WERNER ROOS BERND WURSTER 《Differentiation; research in biological diversity》1978,10(1-3):129-132
Following consumption of the food supply, cells of the cellular slime mould Dictyostelium discoideum aggregate and form a multicellular organism. The mechanism for cell aggregation is chemotaxis. The chemotactic signal in D. discoideum is released periodically from aggregation centers and propagated from cell to cell. cAMP mediates cell aggregation by acting as chemotactic attractant and as propagator of the signal. cAMP signals are measured by cell-surface receptors. Recent evidence indicates a role for cGMP during cAMP-mediated cell aggregation in D. discoideum .
During cell differentiation to aggregation competence, cAMP binding sites appear at the cell surface, and the activity of the enzymes adenylate cyclase and phosphodiesterase increases several-fold. In the present work we investigate the synthesis of cGMP in D. discoideum . Conditions for the assay of guanylate cyclase in cell homogenates are described. Guanylate cyclase activity was followed during cell differentiation to aggregation competence and found to increase fourfold. These results indicate that cGMP is involved in cell differentiation of D. discoideum . In contrast to adenylate cyclase, which is activated by cAMP, guanylate cyclase was under our conditions activated neither by cAMP, nor by folic acid. 相似文献
During cell differentiation to aggregation competence, cAMP binding sites appear at the cell surface, and the activity of the enzymes adenylate cyclase and phosphodiesterase increases several-fold. In the present work we investigate the synthesis of cGMP in D. discoideum . Conditions for the assay of guanylate cyclase in cell homogenates are described. Guanylate cyclase activity was followed during cell differentiation to aggregation competence and found to increase fourfold. These results indicate that cGMP is involved in cell differentiation of D. discoideum . In contrast to adenylate cyclase, which is activated by cAMP, guanylate cyclase was under our conditions activated neither by cAMP, nor by folic acid. 相似文献
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Effects of soil frost on nitrogen net mineralization, soil solution chemistry and seepage losses in a temperate forest soil 总被引:1,自引:0,他引:1
KERSTIN HENTSCHEL WERNER BORKEN TOBIAS ZUBER CHRISTINA BOGNER† BERND HUWE† EGBERT MATZNER 《Global Change Biology》2009,15(4):825-836
Freezing and thawing may alter element turnover and solute fluxes in soils by changing physical and biological soil properties. We simulated soil frost in replicated snow removal plots in a mountainous Norway spruce stand in the Fichtelgebirge area, Germany, and investigated N net mineralization, solute concentrations and fluxes of dissolved organic carbon (DOC) and of mineral ions (NH4 + , NO3 − , Na+ , K+ , Ca2+ , Mg2+ ). At the snow removal plots the minimum soil temperature was −5 °C at 5 cm depth, while the control plots were covered by snow and experienced no soil frost. The soil frost lasted for about 3 months and penetrated the soil to about 15 cm depth. In the 3 months after thawing, the in situ N net mineralization in the forest floor and upper mineral soil was not affected by soil frost. In late summer, NO3 − concentrations increased in forest floor percolates and soil solutions at 20 cm soil depth in the snow removal plots relative to the control. The increase lasted for about 2–4 months at a time of low seepage water fluxes. Soil frost did not affect DOC concentrations and radiocarbon signatures of DOC. No specific frost effect was observed for K+ , Ca2+ and Mg2+ in soil solutions, however, the Na+ concentrations in the upper mineral soil increased. In the 12 months following snowmelt, the solute fluxes of N, DOC, and mineral ions were not influenced by the previous soil frost at any depth. Our experiment did not support the hypothesis that moderate soil frost triggers solute losses of N, DOC, and mineral ions from temperate forest soils. 相似文献
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ANDREAS BAUMANN WERNER FESER PETER CRAMER RASOUL S. KERDAR HARTMUT BLODE JURGEN KORBER 《Biomarkers》2013,18(3):188-202
In the present study, a new in vitro model combining the short-term incubation of precision-cut human liver slices with DNA-adduct analysis by the 32P-postlabelling technique is proposed for investigation of the genotoxic potential of xenobiotics. For method validation, the metabolic turnover of testosterone (TES) and the DNA-adduct inducing potential of 2-aminofluorene (2-AF) were used. Precision-cut human liver slices were prepared from a total of 12 human liver samples which were freshly obtained as parts of resectates from liver surgery. The slices were incubated as submersion cultures with TES and 2-AF for up to 6 h in 12-well tissue culture plates at concentrations of 10-50 and 0.06-28 μM, respectively. Slices recovered from the slicing procedure in the 4 °C cold Krebs-Henseleit buffer as indicated by intracellular potassium concentrations which increased for 2 h and then remained stable until the end of the incubation. TES was extensively metabolized by human liver slices with a similar metabolite pattern as observed in vivo. Almost 90% of the metabolites were conjugates. Major phase-I metabolites were androstendione, 6β-OH-androstendione, 6β-OH-TES, and 15β-OHTES. After incubation with 2-AF, substance related DNA-adducts were detected which increased dose-dependently from 12 to 1146 adducts per 109 nucleotides. The adduct pattern consisted of one major adduct spot, A, representing 80-90% of the total adduct level and up to four minor adduct spots, B-E. In summary, the present data demonstrate that precision-cut liver slices are a valuable alternative in vitro system for DNA-adduct determination to screen chemicals for potential genotoxicity in humans. 相似文献
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CRISTINA FIERA WERNER ULRICH 《Biological journal of the Linnean Society. Linnean Society of London》2012,105(3):498-506
Using a large database on the spatial distribution of European springtails (Collembola) we investigated how range sizes and range distribution across European countries and major islands vary. Irrespective of ecological guild, islands tended to contain more endemic species than mainland countries. Nestedness and species co‐occurrence analysis based on country species lists revealed latitudinal and longitudinal gradients of species occurrences across Europe. Species range sizes were much more coherent and had fewer isolated occurrences than expected from a null model based on random colonization. We did not detect clear postglacial colonization trajectories that shaped the faunal composition across Europe. Our results are consistent with a multiregional postglacial colonization. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 498–506. 相似文献
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