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Rapid, sequential changes in surface morphology of PC12 pheochromocytoma cells in response to nerve growth factor 总被引:20,自引:17,他引:20 下载免费PDF全文
The effect of nerve growth factor (NGF), a substance that promotes the differentiation and maintenance of certain neurons, was studied via scanning electron microscopy utilizing the PC12 clonal NGF-responsive pheochromocytoma cell line. After 2-4 d of exposure to NGF, these cells acquire many of the properties of normal sympathic neurons. However, by phase microscopy, no changes are discernible within the first 12-18 h. Since the primary NGF receptor appears to be a membrane receptor, it seemed likely that some of the initial responses to the factor may be surface related. PC12 cells maintained without NGF are round to ovoid and have numerous microvilli and small blebs. After the addition of NGF, there is a rapidly initiated sequential change in the cell surface. Ruffles appear over the dorsal surface of the cells with 1 min, become prominent by 3 min, and almost disappear by 7 min. Microvilli, conversely, disappear as the dorsal ruffles become prominent. Ruffles are seen at the the periphery of cell at 3 min, are prominent on most of the cells by 7 min and are gone by 15 min. The surface remains smooth from 15 min until 45 min when large blebs appear. The large blebs are present on most cells at 2 h and are gone by 4 h. The surface remains relatively smooth until 6-7 h of NGF treatment, when microvilli reappear as small knobs. These microvilli increase in both number and length to cover the cell surface by 10 h. These changes were not observed with other basic proteins, with α-bungarotoxin (which binds specifically to PC12 membranes), and were not affected by an RNA synthesis inhibitor that blocks initiation of neurite outgrowth. Changes in the cell surface architecture appear to be among the earlist NGF responses yet detected and may represent or reflect primary events in the mechanism of the factor’s action. 相似文献
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Lathe WC rd; Burke WD; Eickbush DG; Eickbush TH 《Molecular biology and evolution》1995,12(6):1094-1105
R1 is a non-long terminal repeat (non-LTR) retrotransposable element that
inserts into a specific sequence of insect 28S ribosomal RNA genes. We have
previously shown that this element has been maintained through vertical
transmission in the melanogaster species subgroup of Drosophila. To address
whether R1 elements have been vertically transmitted for longer periods of
evolutionary time, the analysis has been extended to 11 other species from
four species groups of the genus Drosophila (melanogaster, obscura,
testecea, and repleta). All sequenced elements appeared functional on the
basis of the preservation of their open-reading frames and consistently
higher rate of substitution at synonymous sites relative to replacement
sites. The phylogenetic relationships of the R1 elements from all species
analyzed were congruent with the species phylogenies, suggesting that the
R1 elements have been vertically transmitted since the inception of the
Drosophila genus, an estimated 50-70 Mya. The stable maintenance of R1
through the germ line appears to be the major mechanism for the widespread
distribution of these elements in Drosophila. In two species, D.
neotestecea of the testecea group and D. takahashii of the melanogaster
group, a second family of R1 elements was also present that differed in
sequence by 46% and 31%, respectively, from the family that was congruent
with the species phylogeny. These second families may represent occasional
horizontal transfers or, alternatively, they could reflect the ability of
R1 elements to diverge into new families within a species and evolve
independently.
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K M Lakin S J Schipilowa N W Nowikowa J E Rukasenkow W D Pomojnezkij S J Grenadjorow 《Folia haematologica (Leipzig, Germany : 1928)》1986,113(1-2):230-235
The influence of non-steroidal antiphlogistics (NSA, fluor derivatives of phenylanthranilic acid) on fibrinolysis, platelet function, prostaglandin metabolism and pharmacokinetics of indirect anticoagulants was studied in rats and rabbits in vitro and in vivo. NSA were found to shorten the euglobulin lysis time and to enlarge the lysis zones on fibrin plates. They potentiated the fibrinolytic activity of streptokinase and trypsin. Furthermore, they inhibited platelet aggregation induced by arachidonic acid in rabbits. NSA in combination with inhibitors of thromboxane synthetase potentiated inhibition of aggregation. After oral administration, NSA inhibited formation of thromboxane A2 and prostacyclin in rabbits in a dose-dependent manner. At comparatively low doses, thromboxane A2 synthesis was more effectively inhibited than prostacyclin formation. Due to pharmacokinetic interactions NSA enhanced the anticoagulant effect of indirect anticoagulants and accelerated their distribution and elimination. 相似文献
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