The hypomethylating agent 5-azacytidine (5-azaC) has been shown to reactivate certain X-linked genes. In order better to understand the cellular responses to this cytosine analog, the replication pattern of the inactive X chromosome was studied using the terminal bromodeoxyuridine technique. The replication pattern of the inactive X was altered from late to early in normal female lymphocytes exposed to various concentrations of 5-azaC. There was a direct correlation between the exposure time and the frequency of X chromosomes with variant replication patterns when different exposure schemes were analyzed. There was no apparent difference in the response to 5-azaC between B- and T-lymphocytes. Lymphocytes from an individual with multiple X chromosomes in the presence of a Y (48,XXXY) were also exposed to 5-azaC and demonstrated distinct alterations in the timing of X chromosome replication. Female lymphocytes were also exposed to other S-specific agents (L-ethionine and cytosine arabinoside) and the response was comparable to that seen with 5-azaC. No gross alteration was observed in the replication timing of the autosomes of cells with variant X's Studies were performed on the incidence of earlier replicating X chromosomes in lymphocytes from normal women throughout the menstrual cycle and definite cyclic fluctuation patterns were observed. The replication pattern of the inactive X in human tumor cell lines with multiple X chromosomes was analyzed after 5-azaC treatment and was much greater than that seen in normal cells. In order to determine alterations in methylation, DNA from tumor cells before and after 5-azaC treatment was digested with the isoschizomers, MspI and HpaII. Two oncogenes were analyzed and their methylation status had not changed due to 5-azaC These studies have provided cytogenetic data concerning 5-azaC-induced changes in replication timing and are important for clarifying the mechanism controlling X inactivation and its possible link to tumor progression / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_25453 |
| Date | January 1990 |
| Contributors | Gregory, Paula Elizabeth (Author), Wang, Nancy (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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