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排序方式: 共有137条查询结果,搜索用时 15 毫秒
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Rapid, sequential changes in surface morphology of PC12 pheochromocytoma cells in response to nerve growth factor 总被引:37,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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RNA polymerase II primes Polycomb‐repressed developmental genes throughout terminal neuronal differentiation 下载免费PDF全文
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Previous investigations on the monkey kidney COS cell line demonstrated the
weak expression of fucosylated cell surface antigens and presence of
endogenous fucosyltransferase activities in cell extracts. RT-PCR analyses
have now revealed expression of five homologs of human fucosyltransferase
genes, FUT1, FUT4, FUT5, FUT7, and FUT8, in COS cell mRNA. The enzyme in
COS cell extracts acting on unsialylated Type 2 structures is closely
similar in its properties to the alpha1,3- fucosyltransferase encoded by
human FUT4 gene and does not resemble the product of the FUT5 gene.
Although FUT1 is expressed in the COS cell mRNA, it has not been possible
to demonstrate alpha1,2- fucosyltransferase activity in cell extracts but
the presence of Le(y) and blood-group A antigenic determinants on the cell
surface imply the formation of H-precursor structures at some stage. The
most strongly expressed fucosyltransferase in the COS cells is the
alpha1,6-enzyme transferring fucose to the innermost N -acetylglucosamine
unit in N - glycan chains; this enzyme is similar in its properties to the
product of the human FUT8 gene. The enzymes resembling the human FUT4 and
FUT8 gene products both had pH optima of 7.0 and were resistant to 10 mM
NEM. The incorporation of fucose into asialo-fetuin was optimal at 5.5 and
was inhibited by 10 mM NEM. This result initially suggested the presence of
a third fucosyltransferase expressed in the COS cells but we have now shown
that triantennary N- glycans with terminal nonreducing galactose units,
similar to those present in asialo-fetuin, are modified by a weak
endogenous beta-galactosidase in the COS cell extracts and thereby rendered
suitable substrates for the alpha1,6- fucosyltransferase.
相似文献
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M Kale R Ramsey-Goldman S Bernatsky MB Urowitz D Gladman PR Fortin M Petri E Yelin S Manzi S Edworthy O Nived S-C Bae D Isenberg A Rahman JG Hanly C Gordon S Jacobsen E Ginzler DJ Wallace GS Alarcón MA Dooley L Gottesman K Steinsson A Zoma J-L Senécal S Barr G Sturfelt L Dreyer L Criswell J Sibley JL Lee AE Clarke 《Arthritis research & therapy》2012,14(Z3):A15
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