Doctor of Philosophy (PhD)
The first part of this work induced T-cell lymphoma in mice by employing a breeding scheme involving mouse strains expressing the KrasG12D oncoprotein and mice expressing cyclic recombinase from the mouse mammary tumor virus promoter. Imprinted domains were then systematically surveyed for DNA methylation changes during tumor progression using combined bisulfite restriction analysis and next-generation-bisulfite-sequencing. Hyper-or hypomethylation was detected at the imprinting control regions (ICRs) of the Dlk1, Peg10, Peg3, Grb10 and Gnas domains. These DNA methylation changes at ICRs were more prevalent and consistent than those observed at the promoter regions of well-known tumor suppressors, such as Mgmt, Fhit and Mlh1. Thus, the changes observed at these imprinted domains are the outcome of isolated incidents affecting DNA methylation settings. Within imprinted domains, DNA methylation changes tend to be restricted to ICRs as nearby somatic differentially methylated regions and promoter regions experience no change. Furthermore, detailed analyses revealed that small cis-regulatory elements within ICRs tend to be resistant to DNA methylation changes, suggesting potential protection by unknown trans-factors. The second part of this work further characterized the epigenetic response of imprinted domains during carcinogenesis. This study compared the stability of DNA methylation at a variety if cis-regulatory elements within imprinted domains in two fundamentally different mouse tumors, benign and malignant. The data suggest that imprinted domains remain quite stable in benign processes, but are highly susceptible to epigenetic alterations in infiltrative lesions. The preservation of DNA methylation within imprinted domains in benign tumors throughout their duration suggests that imprinted genes are not involved with the initiation of carcinogenesis or the growth of tumors. However, the frequent detection of DNA methylation changes at imprinting control regions in infiltrative lesions suggest that imprinted genes are associated with tumor cells that have gained the ability to defy tissue boundaries. Overall, this study demonstrates that imprinted domains are targeted for DNA hypermethylation when benign tumor cells transition to malignant. Thus, monitoring DNA methylation within imprinted domains may be useful in evaluating the progression of neoplasms.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Bretz, Corey Lane, "Epigenetic Response of Imprinted Domains during Carcinogenesis" (2017). LSU Doctoral Dissertations. 4373.