Deregulation of both imprinted and expressed alleles of the insulin-like growth factor 2 gene during beta-cell tumorigenesis.

In a mouse model of multistage carcinogenesis elicited by the SV40 large T-antigen (Tag) oncogene in pancreatic beta cells, the gene for insulin-like growth factor IGF2 is focally up-regulated and functionally implicated in tumour development. The IGF2 gene is differentially regulated in normal tissues: the paternal allele is transiently expressed during embryogenesis, whereas the maternal allele is genomically imprinted and inactive. Crossbred mice carrying the Tag oncogene and a disruption of either the paternal or maternal allele of IGF2 reveal that both alleles are co-activated early during tumour development, and that each contributes to malignant hyperproliferation and consequent tumour volume.