H19 and Igf2 monoallelic expression is regulated in two distinct ways by ashared cis acting regulatory region upstream of H19

H19 and Igf2 are expressed in a monoallelic fashion from the maternal and p aternal chromosomes, respectively. A region upstream of H19 has been shown to regulate such imprinted expression of both genes in cis. We have taken a dvantage of a loxP/cre recombinase-based strategy to delete this region in mice in a conditional manner to determine the temporal requirement of the u pstream region in initiating and maintaining the imprinted expression of H1 9 and Igf2. Analysis of allele-specific expression of H19 and Igf2 and DNA methylation at the H19 promoter demonstrates that this region controls the monoallelic expression of the two genes in different ways, suggesting that it harbors two functionally distinct regulatory elements. Continued presenc e of the region is required to silence maternal Igf2 in accordance with its proposed role as an insulator. However, it does not have a direct role in keeping the paternal H19 promoter silenced. Instead, on the paternal chromo some, the upstream element mediates epigenetic modifications of the H19 pro moter region during development, leading to transcriptional silencing of H1 9. Thereafter, its presence is redundant for preventing transcription. Pres ently, this temporal requirement of the silencing element appears to be a u nique cis activity in the mammalian system. However, it is likely that othe r cis-acting elements, positive and negative, have the ability to effect st able changes in the chromatin structure and are not constantly required to give signals to the transcriptional machinery.