Epigenetic mechanisms restrict the expression of imprinted genes to one parental 
allele in diploid cells. At the Igf2r/Air imprinted cluster on mouse chromosome 
17, paternal-specific expression of the Air noncoding RNA has been shown to 
silence three genes in cis: Igf2r, Slc22a2, and Slc22a3. By an unbiased mapping 
of DNase I hypersensitive sites (DHS) in a 192-kb region flanking Igf2r and Air, 
we identified 21 DHS, of which nine mapped to evolutionarily conserved 
sequences. Based on the hypothesis that silencing effects of Air would be 
directed towards cis regulatory elements used to activate genes, DHS are 
potential key players in the control of imprinted expression. However, in this 
192-kb region only the two DHS mapping to the Igf2r and Air promoters show 
parental specificity. The remaining 19 DHS were present on both parental alleles 
and, thus, have the potential to activate Igf2r on the maternal allele and Air 
on the paternal allele. The possibility that the Igf2r and Air promoters share 
the same cis-acting regulatory elements, albeit on opposite parental 
chromosomes, was supported by the similar expression profiles of Igf2r and Air 
in vivo. These results refine our understanding of the onset of imprinted 
silencing at this cluster and indicate the Air noncoding RNA may specifically 
target silencing to the Igf2r promoter.