Abstract: Alyssa Gagne
Mentor: Dr. Davis
There is an unusual form of gene regulation in mammals known as genomic imprinting. In general, most genes express both the maternal and paternal copy, contributing equally to the overall expression of the gene. In contrast, for imprinted genes, only one of the two copies of the gene, either the maternal or paternal copy, is expressed and this regulation is controlled at the level of transcription. This is known as monoallelic expression.
Mammalian cells need to be able to distinguish which parental allele is to be transcribed for proper expression. The parental origin of the expressed allele can be distinguished by the cell through epigenetics, or modifications to the DNA that aid in the regulation of transcription. One method of distinguishing the parental alleles is differential DNA methylation. DNA is methylated when certain nucleotides are modified through the addition of a methyl group. Differential methylation of the paternal alleles allows for them to be distinguished from each other because they are structured differently. When methylation is present, the structure of the DNA will be changed as compared to the unmethylated allele, allowing for its association with different proteins and transcription factors—leading to differential expression of the alleles.
If the regulation of gene expression is in part controlled by imprinting through differential DNA methylation, when is this methylation acquired? My research will examine the timing of methylation acquisition of the imprinted gene Dlk1 in mouse. Dlk1 is located in a cluster with another imprinted gene, Gtl2. Gtl2 contains two differentially methylated regions (DMRs) that are methylated on the paternal allele. The IG-DMR region is methylated in the sperm and inherited at fertilization, whereas the Gtl2-DMR acquires its methylation during embryonic development. The gene that is the focus of this project, Dlk1, contains a third DMR known to be methylated on the paternal allele in adult tissues. In the project, I will be analyzing the methylation patterns of the Dkl1-DMR at different stages of development to identify when the paternal allele-specific methylation is acquired—and comparing the results to what is already known about the Gtl2-DMR. After the timing of the post-fertilization methylation has been determined for the Dlk1-DMR, ultimately we will be able to compare the patterning to that of the Gtl2-DMR. Because both Dlk1 and Gtl2 are located in the same imprinting cluster, we might expect that the methylation is acquired at similar times, but currently the information regarding the regulation of DMRs within an imprinting cluster is unknown.