OPPOSITELY IMPRINTED GENES-H19 AND INSULIN-LIKE GROWTH FACTOR-II ARE COEXPRESSED IN HUMAN ANDROGENETIC TROPHOBLAST

Human uniparental gestations such as gynogenetic ovarian teratomas and androgenetic complete hydatidiform moles provide a model to evaluate the integrity of parent-specific gene expression-i.e, imprinting-in th e absence of a complementary parental genetic contribution. We studied expression, in these tissues, of the oppositely imprinted genes H19, which is an embryonic nontranslated RNA, and insulin-like growth facto r type 2 (IGF2). Normal gestations only express H19 from the maternal allele and express IGF2 from the paternal allele, whereas neither is e xpressed from the maternal genome of gynogenetic gestations, and both are expressed from the paternal genome of androgenetic gestations. Coe xpression of H19 and IGF2 in the androgenetic tissues was in a single population of cells, mononuclear trophoblast-the same cell type expres sing these genes in biparental placentas. These results demonstrate th at a biparental genome may be required for expression of the reciproca l IGF2/H19 imprint. Alternatively, biparental expression may be a norm al feature of some imprinted genes in specific cell types. Additional experiments with other imprinted genes will clarify whether this refle cts global failure of the imprinting process or a change specific to t he IGF2/H19 locus.