Establishment of Paternal Genomic Imprinting in Mouse Prospermatogonia Analyzed by Nuclear Transfer

ABSTRACT In mice, the establishment of paternal genomic imprinting in male germ cells starts at midgestation, as suggested by DNA methylation analyses of differentially methylated regions (DMRs). However, this information is based on averages from mixed populations of germ cells, and the DNA methylation pattern might not always provide a full representation of imprinting status. To obtain more detailed information on the establishment of paternal imprinting, single prospermatogonia at Embryonic Days 15.5 (E15.5), E16.5, and E17.5 and at Day 0.5 after birth were cloned using nuclear transfer; previous reports suggested that cloned embryos reflected the donor's genomic imprinting status. Then, the resultant fetuses (E9.5) were analyzed for the DNA methylation pattern of three paternal DMRs (IG-DMR, H19 DMR, and Rasgrf1 DMR) and the expression pattern of imprinted genes therein. The overall data indicated that establishment of genomic imprinting in all paternally imprinted regions was completed by E17.5, fol...