Preferential Loss of Heterozygosity of Chromosome 7 Loci in Simian Virus 40 t/T Antigen-Induced Mouse Hepatocellular Carcinomas Does Not Involve H-<i>ras</i> Muatations

Genetic complementation experiments have indicated that both a maternal and a paternal copy of the distal region of mouse chromosome 7 are essential for normal development [1]. This suggested the presence of genes whose expression is dependent on the gamete of origin in this chromosomal region. Two such imprinted genes, namely insulin-like growth factor II ( Igf 2) and H 19, have been identified so far [2, 3]. The first encodes a peptide with mitotic activity towards several cell types, that contributes significantly to prenatal growth of mammals, whereas the second has, as yet, no defined role and seems not to encode any protein, but works as RNA. ( Igf 2) and H19 are located 90 kb apart, have similar expression patterns during development and are reciprocally imprinted, since the maternal Igf 2 and the paternal H19 alleles are inactive in most fetal tissues [4, 5].