PROMOTER-DEPENDENT TISSUE-SPECIFIC EXPRESSIVE NATURE OF IMPRINTING GENE, INSULIN-LIKE GROWTH-FACTOR-II, IN HUMAN TISSUES

The insulin-like growth factor II (IGF2) is a polypeptide with structu re homology to insulin which possesses mitogen activity, and imprinted with paternal allele, In order to elucidate the distribution of impri nting pattern and relationship between allele- and tissue-specific exp ression of IGF2 in growth and maturation of human tissues, we investig ated allele-specific expression of IGF2 in a wide spectrum of normal m aturated human tissues by a PCR-based assay and found monoallelic expr ession in all eight-type tissues tested except human adult liver, More over, when a RT-PCR based sensitive allele-specific primer extension f or an Apa I polymorphism within exon 9 of IGF2 was used, the analysis revealed the gene was normally imprinted in placenta; in contrast to t he finding with placenta, IGF2 transcripts were biallelically expresse d in human adult liver. Our results have clearly demonstrated preferen tial paternal expression and tissue-specific imprinting pattern of IGF 2 in all human tissues tested in this study. Collectively, since IGF2 expression in developing fetal and adult liver is specified by distinc t promoters, these extensive observations definitively indicate that t ranscriptional imprinting of IGF2 is more likely a promoter dependent manner. (C) 1997 Academic Press.