Use of a novel system for defining a gene imprinting region.

Gene imprinting involves the expression of a single allele, depending on its parental origin. In this report, we describe the use of a novel system, implementing human tissues exclusively endowed with either maternally or paternally inherited chromosomes, to better define a known gene imprinting region. Specific RNA transcripts for Placental Ribonuclease Inhibitor (PRI) and Cathepsin D were analysed by northern blotting for expression in complete hydatidiform mole, mature teratoma, and normal placenta. These genes are in close proximity to the reciprocally imprinted H19 and IGF-2 genes found on chromosome 11p15.5. Since all the tissues studied expressed Cathepsin D and PRI, these are not, by definition, imprinted, but as yet we cannot define the borders of the imprinting area on chromosome 11p15.5.