Characterization of a novel fluorescent reporter of genomic imprinting in the mouse

Regulation of inserted transcriptional units by epigenetic means has been reported for many years, and has been used to study characteristics of epigenetic regulation. Some of these transgenes have become regulated by genomic imprinting, and thus are expressed from only one of the two parental chromosomes and, occasionally, acquire parent-of-origin-specific epigenetic markings such as DNA methylation. These transgenes in particular have been useful in elucidating mechanisms of imprinted regulation. Here is described the first imprinted fluorescent transgene, a green fluorescent protein (GFP) gene inserted in the distal MMU7 imprinted domain between the imprinting centers 1 and 2 (IC1 and IC2) regulated regions. This transgene, called Tel7KI, exhibits imprinted expression only from the maternal allele, and is silenced and DNA methylated on the paternal allele in post-implantation embryos. In the embryo this allele-specificity is consistent throughout all tissues and developmental stages analyzed except the developing germ line, making Tel7KI a potential reporter of epigenetic reprogramming in that lineage. In the placenta, imprinted expression and DNA methylation of Tel7KI is lost, and both alleles are expressed and methylated at moderate levels. Finally, an analysis of the effect of IC2 on silencing of Tel7KI in an embryonic stem cell differentiation assay revealed a possible extension of the region of influence for that imprinting centre a further 300kb proximal. Thus, Tel7KI has the potential to be an extremely useful tool in the study of genomic imprinting.Medicine, Faculty ofMedical Genetics, Department ofGraduat