AbstractDNA methylation or 5-methylcytosine (5mC) is an important epigenetic mark integral to appropriate genomic imprinting, X chromosome inactivation and in the silencing of developmentally important genes. There remains to be a lot unknown about how DNA methylation is programmed and reprogrammed once lost particulary in early mammalian development. In untransformed hTERTs and in mouse embryonic stem cells (mESCs) we were able to investigate how methylation can or cannot be recovered following the removal and reintroduction of key methyltransferases, by using a range of wet-lab and bioinformatic approaches to assay methylation at individual CpG sites. Indeed, this thesis has shown that methylation, once lost is able to be recovered in nearly all of the known and putative imprints assayed in the mESCs through rescue with DNMT3A2. Not only does the de novo methyltransferase-3a assist with the recovery of methylation but it also plays a role in maintenance methylation.
A reduction of methylation through a stable loss of DNMT1 in the hTERTs however highlighted enriched groups of hypomethylated genes such as the Cancer Testis Antigen (CTA) genes and the Protocadherins (PCDH) that are sentistive to this loss, and in some instances associated with polycomb marks. Interestingly a transient loss of methylation however in the same system with pharmacological 5-aza-2dC (Aza) showed not only widespread methylation, but also some gains of methylation at selected loci such as the the GPCRs known to act as oncogenes and tumour supressors. In conclusion, through examining the effects of the loss of DNA methylation in both human and mouse model systems, this thesis has successfully identified gene classes sensitive to a transient and stable loss of DNA methylation and identified where this methylation can be recovered.
|Date of Award||Apr 2019|
|Supervisor||Colum Walsh (Supervisor) & Declan Mc Kenna (Supervisor)|