Genomic regions regulating imprinting and insulin-like growth factor-II promoter 3 activity in transgenics: novel enhancer and silencer elements.

Transgenic lines (89) were made with constructs containing eight different combinations of candidate regulatory elements from the insulin-like growth factor-II (Igf2)-H19 region of mouse chromosome 7. In all constructs, promoter 3 of Igf2 was attached to a firefly luciferase reporter gene. Promoter 3 was the common element that imposed a decrease in reporter activity similar to that of endogenous Igf2 after birth. The specific activity of the reporter was measured on the day of birth in the liver and the brain, after each transgene had been transmitted by either the father or the mother. This procedure demonstrated that the quantity and organ distribution of expression from this promoter can be regulated by each element. The following new information was obtained. (a) The 5' differentially methylated region of Igf2 inhibits promoter 3 in the liver. (b) The conserved DNase I-hypersensitive Middle region between Igf2 and H19 is an enhancer of promoter 3 in the brain. (c) The H19 promoter inhibits Igf2 promoter 3 in the brain. The results confirmed that the H19 enhancer is a strong enhancer of promoter 3 in the liver. A new finding was that one genomic region regularly imposed imprinted gene expression. This was the H19 enhancer, and this region was sufficient to give higher expression on maternal transmission in the majority of transgenic lines. The full data are reported in Supplementary Publication SUP 50180 (8 pages), which has been deposited at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1997) 21, 8-10.