LOSS OF THE MATERNAL H19 GENE INDUCES CHANGES IN IGF2 METHYLATION IN BOTH CIS AND TRANS

Recent investigations have shown that the maintenance of genomic impri nting of the murine insulin-like growth factor 2 (Igf2) gene involves at least two factors: the DNA (cytosine-5-)-methyltransferase activity , which is required to preserve the paternal specific expression of Ig f2, and the H19 gene (lying 90 kb downstream of Igf2 gene), which upon inactivation leads to relaxation of the Igf2 imprint. It is not yet c lear how these two factors are related to each other in the process of maintenance of Igf2 imprinting and, in particular, whether the latter is acting through cis elements or whether the H19 RNA itself is invol ved, By using Southern blots and the bisulfite genomic-sequencing tech nique, we have investigated the allelic methylation patterns (epigenot ypes) of the Igf2 gene in two strains of mouse with distinct deletions of the H19 gene, The results show that maternal transmission of H19 g ene deletions leads the maternal allele of Igf2 to adopt the epigenoty pe of the paternal allele and indicate that this phenomenon is influen ced directly or indirectly by the H19 gene expression. More importantl y, the bisulfite genomic-sequencing allowed us to show that the methyl ation pattern of the paternal allele of the Igf2 gene is affected in t rans by deletions of the active maternal allele of the H19 gene, Selec tion during development for the appropriate expression of Igf2, dosage -dependent factors that bind to the Igf2 gene, or methylation transfer between the parental alleles could be involved in this trans effect.