Rasgrf1 (RAS protein-specific guanine nucleotide-releasing factor 1) is paternally expressed, but
the maternal allele is expressed at low levels (<10% of paternal levels) in brain (Plass
C et al, 1996). Paternal expression is dependent on paternal methylation of a 41 bp direct
tandem repeat (40 copies) 30 kb upstream of Rasgrf1 (Pearsall
RS et al, 1999; Yoon
BJ et al, 2002; de
la Puente A et al 2002).
Yoon et al identified a repeated sequence 3' of the differentially methylated domain (DMD) that
regulates imprinted expression (Yoon
B et al, 2005).