Elucidation of the minimal sequence required to imprint H19 transgenes

The imprinted mouse H19 gene exhibits maternal allele-specific expression a nd paternal allele-specific hypermethylation. We previously demonstrated th at a 14-kb H19 minitransgene possessing 5 ' differentially methylated seque nce recapitulates the endogenous H19 imprinting pattern when present as hig h-copy arrays, To investigate the minimal sequences that are sufficient for H19 transgene imprinting, we have tested new transgenes in mice. While tra nsgenes harboring limited or no 3 ' H19 sequence indicate that multiple ele ments within the 8-kb 3 ' fragment are required for appropriate imprinting, transgenes incorporating 1.7 lib of additional 5 ' sequence mimic the endo genous H19 pattern, including proper imprinting of low-copy arrays. One of these imprinted lines had a single 15.7-kb transgene integrant. This is the smallest H19 transgene identified thus far to display imprinting propertie s characteristic of the endogenous gene, suggesting that all cis-acting ele ments required for H19 imprinting in endodermal tissues reside within the 1 5.7-kb transgenic sequence. (C) 2001 Academic Press.