Investigation into the epigenetic events leading to heritable silencing of Cdkn1c

In mammals, there are subsets of genes that are only expressed from one parental allele. This phenomenon, known as genomic imprinting, relies on epigenetic marks to distinguish between the two parental alleles. These epigenetic marks are erased and re-established in the germ line of every generation. Cdkn1c is an imprinted gene in humans and mice. Maternal specific expression of Cdkn1c depends on a germ line DNA methylation mark at a distant cis element (KvDMRl), also known as the imprint control region. When DNA methylation is lost at KvDMRl, Cdkn1c expression is suppressed. On the paternal allele, silencing of Cdkn1c is associated with the expression of a distantly located non-coding RNA (Kcnqlotl/Litl) overlapping the KvDMRl, which is presumed to mediate silencing through the formation of heterochromatin. In somatic cells, long term full silencing of paternal Cdkn1c is maintained by DNA methylation at a CpG island within Cdkn1c. We have shown that embryonic germ (EG) cells, derived from 12.5 dpc primordial germ cells, are a good model for studying the early epigenetic events that lead to heritable silencing of imprinted genes. Cdkn1c expression was suppressed in differentiated EG cells compared to embryonic stem (ES) cells indicating that this domain is silent in EG cells. The Cdkn1c CpG island was hypomethylated in both undifferentiated and differentiated EG cells and was also hypomethylated in ES and androgenetic (AG) stem cells indicating that DNA methylation was not required for silencing Cdkn1c. Suppression of Cdkn1c was likely due to the acquirement of repressive histone marks. H3K27me3 was found enriched at the Cdkn1c promoter in differentiated EG cells and in undifferentiated and differentiated AG cells but was absent in undifferentiated EG cells indicating that this mark was specifically recruited during EG cell differentiation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo