Role of a 461-bp G-rich repetitive element in H19 transgene imprinting

The molecular mechanism leading to the im printed expression of genes is po orly understood. While no conserved cis-acting elements have been identifie d within the known loci, many imprinted genes are located near directly rep etitive sequence elements, suggesting that such repeats might play a role i n imprinted gene expression. The maternally expressed mouse H19 gene is loc ated approximately 1.5 kb downstream from a 461-bp G-rich repetitive elemen t. We have used a transgenic model to investigate whether this element is e ssential for H19 imprinting. Previous results demonstrated that a transgene , which contains 14 kb of H19 sequence, exhibits parent-of-origin specific expression and methylation analogous to the endogenous H19 imprinting patte rn. Here, we have generated transgenes lacking the G-rich repeat. One trans gene, containing a deletion of the G-rich repetitive element but which incl udes an additional 1.7 kb of 5' H19 sequence, is imprinted similarly to the endogenous H19 gene. To determine whether the G-rich repeat is conserved i n other imprinted mammalian H19 homologues, additional 5' flanking sequence s were cloned from the rat and human. This element is conserved in the rat but not in human DNA. These results suggest that the 461-bp G-rich repetiti ve element is not essential for H19 imprinting.