ISSN:
1572-9931
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract We have analyzed patterns of DNA replication in X chromosomes from diploid cultured human fibroblasts and from three triploid 69,XXY fibroblast strains, using BrdU-33258 Hoechst—Giemsa techniques. Both X chromosomes in each of these Barr body-negative triploid strains were early-replicating. The results of gene dosage studies using (1) a histochemical stain to measure X-linked glucose-6-phosphate dehydrogenase (G6PD) activity in single cells and (2) cellulose acetate electrophoresis of G6PD activity in cell extracts also indicated that both Xs in these strains were genetically active. When we compared the synchrony of X chromosome DNA replication kinetics both between cells and within cells containing multiple inactive Xs, a marked variability and asynchrony was observed for latereplicating X chromosomes. In a culture of 47,XXX fibroblasts administered an 8-h terminal pulse of dT after growth in BrdU-containing medium, asynchrony was detected between the two late-replicating Xs in ∼70% of cells examined. No such asynchrony was observed between the two earlyreplicating Xs in similarly cultured 69, XXY cells; in the triploid strains, the two Xs were distinguished by asynchronous replication in only ∼15% of cells. The striking variability in late X chromosome replication kinetics appears, then, to be a property unique to inactive Xs and is not inherent to all X chromosomes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01538795
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