CHARACTERIZATION OF A METHYLATION IMPRINT IN THE PRADER-WILLI-SYNDROME CHROMOSOME REGION

In adult human tissues, a Hpall and a Cfol restriction site at the PW7 1 (D15S63) locus in the Prader-Willi syndrome region on chromosome 15 are methylated on the maternal chromosome, but unmethylated on the pat ernal chromosome. The Hpall site is part of a sequence with high homol ogy to the long terminal repeat of human endogenous retroviruses. Anot her Hpall site at the PW71 locus is methylated on both chromosomes. Sp erm DNA carries the adult paternal methylation pattern. Oocyte DNA cou ld not be studied. In chorion, placenta and tumor DNA, both Hpall site s are unmethylated. These findings suggest that the PW71 methylation i mprint is established in the germline and that extraembryonic tissues and tumors are hypomethylated.