Deletion of a silencer element disrupts H19 imprinting independently of a DNA methylation epigenetic switch

The H19 imprinted gene is silenced when paternally inherited and active onl y when inherited maternally, This is thought to involve a cis-acting contro l region upstream of H19 that is responsible for regulating a number of fun ctions including DNA methylation, asynchronous replication of parental chro mosomes and an insulator, Here we report on the function of a 1.2 kb upstre am element in the mouse, which was previously shown to function as a bidire ctional silencer in Drosophila, The cre-loxP-mediated targeted deletion of the 1.2 kb region had no effect on the maternal allele, However, there was loss of silencing of the paternal allele in many endodermal and other tissu es, The pattern of expression was very similar to the expression pattern co nferred by the enhancer elements downstream of H19, We could not detect an effect on the expression of the neighbouring imprinted Igf2 gene, suggestin g that the proposed boundary element insulating this gene from the downstre am enhancers was unaffected. Despite derepression of the paternal H19 allel e, the deletion surprisingly did not affect the differential DNA methylatio n of the locus, which displayed an appropriate epigenetic switch in the par ental germlines, Furthermore, the characteristic asynchronous pattern of DN A replication at H19 was also not disrupted by the deletion, suggesting tha t the sequences that mediate this were also intact, The silencer is therefo re part of a complex cis-regulatory region upstream of the H19 gene and act s specifically to ensure the repression of the paternal allele, without a p redominant effect on the epigenetic switch in the germline.