Spatially restricted imprinting of mouse chromosome 7

Three of the four known imprinted genes (Igf-2, H19, and Snrpn) map to mouse chromosome 7. We used mRNA phenotyping to examine the tissue-specific transcription of Igf-1r, H-ras-1, and Gabrb3, which map to chromosome 7 between Snrpn and the Igf-2/H19 domain, and Myod-1, which maps proximal to Snrpn. We found that all of these genes were expressed by both parental alleles in tissues from day 1 neonates. The fact that imprinted genes can flank or map closely to genes that escape such epigenetic modification suggests that autosomal imprinting is not manifested globally along imprinted chromosomes but rather is spatially restricted, perhaps even defined by specific DNA consensus sequences or an "imprint box" associated with imprintable genes.