scholarly journals Analysis of chromosome positions in the interphase nucleus of Chinese hamster cells by laser-UV-microirradiation experiments

1982 ◽  
Vol 62 (3) ◽  
pp. 201-209 ◽  
Author(s):  
T. Cremer ◽  
C. Cremer ◽  
T. Schneider ◽  
H. Baumann ◽  
L. Hens ◽  
...  
1976 ◽  
Vol 66 (1) ◽  
pp. 106 ◽  
Author(s):  
Christoph Cremer ◽  
Thomas Cremer ◽  
Christian Zorn ◽  
Lili Schoeller

Author(s):  
Jostein Dahle ◽  
Paul Noordhuis ◽  
Trond Stokke ◽  
Debbie Hege Svendsrud ◽  
Egil Kvam

1989 ◽  
Vol 9 (4) ◽  
pp. 1635-1641 ◽  
Author(s):  
S G Grant ◽  
R G Worton

We have investigated the genetic activation of the hprt (hypoxanthine-guanine phosphoribosyltransferase) gene located on the inactive X chromosome in primary and transformed female diploid Chinese hamster cells after treatment with the DNA methylation inhibitor 5-azacytidine (5azaCR). Mutants deficient in HPRT were first selected by growth in 6-thioguanine from two primary fibroblast cell lines and from transformed lines derived from them. These HPRT- mutants were then treated with 5azaCR and plated in HAT (hypoxanthine-methotrexate-thymidine) medium to select for cells that had reexpressed the hprt gene on the inactive X chromosome. Contrary to previous results with primary human cells, 5azaCR was effective in activating the hprt gene in primary Chinese hamster fibroblasts at a low but reproducible frequency of 2 x 10(-6) to 7 x 10(-6). In comparison, the frequency in independently derived transformed lines varied from 1 x 10(-5) to 5 x 10(-3), consistently higher than in the nontransformed cells. This increase remained significant when the difference in growth rates between the primary and transformed lines was taken into account. Treatment with 5azaCR was also found to induce transformation in the primary cell lines but at a low frequency of 4 x 10(-7) to 8 x 10(-7), inconsistent with a two-step model of transformation followed by gene activation to explain the derepression of hprt in primary cells. Thus, these results indicate that upon transformation, the hprt gene on the inactive Chinese hamster X chromosome is rendered more susceptible to action by 5azaCR, consistent with a generalized DNA demethylation associated with the transformation event or with an increase in the instability of an underlying primary mechanism of X inactivation.


1987 ◽  
Vol 15 (1) ◽  
pp. 30-32
Author(s):  
Michael Garle ◽  
Alison H. Hammond ◽  
Jeffrey R. Fry

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