Differential methylation at the imprinted DLk1 gene in 6.5 and 3.5 day embryos

 

              Epigenetics focuses primarily on the genetic processes that regulate how and when specific genes will be turned on and off. It is the study of changes in gene expression, or molecular phenotype, caused by certain mechanisms other than DNA sequence changes. One standard for identifying the epicontrol of gene expression has been studied through the analysis of a process known as genomic imprinting. Genomic imprinting is a mammalian-specific genetic phenomenon where the expression of certain genes is dependent upon the parent-of-origin and it is controlled at the level of transcription. Each known diploid organism possesses two copies of each gene, one of which is inherited from the mother and the other from the father. Together, both the maternal and paternal alleles contribute equally to the gene expression; however, sometimes the gene is considered to be monoallelically expressed. This means that only the maternally inherited allele or only the paternally inherited allele is expressed, and the allele that isn't expressed is silenced. This type of inheritance pattern is known as genomic imprinting.

              In order to allow for appropriate expression of the monallelic imprinted genes, the cellular machinery involved with transcription must identify the maternal and paternal alleles and regulate their expression. DNA methylation and histone modifications are two epigenetic modification factors known to control the imprinted gene expression. Specifically, DNA methylation occurs when a methyl groups becomes covalently bonded to the cytosine nucleotide. When this happens, it ultimately changes the cytosine structure and allows for the cellular transcriptional machinery to identify between which parental allele will be expressed. Differential DNA methylation of the parental alleles occurs when one parental allele is methylated and the other is not methylated. This results in the differential expression of the parental alleles where parental allele is silenced and the other is expressed. Imprinted genes are sometimes found in clusters, and a single differentially methylated region can influence more than one gene.

              In the last few years, a group of students within the Davis lab have been studying the Dlk1-Gtl2 imprinting cluster in mouse which contains numerous imprinted genes as well as three differentially methylated regions (DMRs) including Dlk1-DMR, Glt2-DMR and IG-DMR. These students have been investigating at what point during development these DMRs acquire differential methylation patterns. By looking specifically at the Dlk1 and Gtl2 genes at various stages of development, the timing of methylation acquisition can be compared. Studying the methylation patterns within lung and liver tissues from newborn and adult mice allows for the further understanding of how methylation patterns change during different developmental stages.

              My project is a continuation of previous work which focused on an analysis of DNA methylation at the Dlk1-DMR. Though a large sum of data has already been collected, I will specifically be looking at the methylation patterns of the Dlk1-DMR in 3.5 and 6.5 day post coitum embryos and shall compare the acquisition of DNA methylation at this site to the pattern at Gtl2-DMR. After, I shall be looking more into the expression patterns of the Dlk1 gene and looking at how these results compare to how the DNA is acquired from the imprinted genes.