No Evidence for a Parent-of-Origin Specific Differentially Methylated Region Linked to RASGRF1

Punita Navnitlal Pitamber, Zané Lombard, Michèle Ramsay

Imprinted genes are expressed from one parental allele in a parent-of-origin manner. This monoallelic behavior is regulated by allele-specific DNA methylation that is confined to differentially methylated regions (DMRs). To date there are over 80 known human imprinted genes of which only three are known to have paternally methylated DMRs. In mice there exists an additional paternally methylated DMR associated with Rasgrf1. The Rasgrf1 gene forms part of the MAPK signaling pathway and plays a role in long-term memory formation and growth control. A RASGRF1-associated parent-of-origin specific DMR in humans and its methylation status in sperm DNA have not been explored. The primary aim of this study was to determine whether the human RASGRF1 gene contains a DMR and whether this DMR is paternally methylated and shows roughly 50% methylation in somatic tissue. Computational assessments were done to identify putative CTCF binding sites, CpG islands (CGIs) that could serve as potential RASGRF1 DMRs and tandem repeats within or adjacent to these CGIs. The methylation status of three putative CGIs was assessed using quantitative pyrosequencing technology. None of the putative CTCF binding sites was found to occur in the predicted CGIs. The three putative CGIs linked to RASGRF1 did not display allele-specific methylation. While one of the three CGIs was found to be hypomethylated in both blood DNA and sperm DNA, the other two were found to be hypermethylated. The CGIs evaluated in this study did not fit the criteria of being a allele-specific DMR. Unlike the mouse Rasgrf1 locus, the human RASGRF1-associated CpG rich regions do not exhibit differential methylation in a parent-of-origin manner.