Spatial separation of parental genomes in preimplantation mouse embryos

We have used two different experimental approaches to demonstrate topologic al separation of parental genomes in preimplantation mouse embryos: mouse e ggs fertilized with 5-bromodeoxyuridine (BrdU)-labeled sperm followed by de tection of BrdU in early diploid embryos, and differential heterochromatin staining in mouse interspecific hybrid embryos. Separation of chromatin acc ording to parental origin was preserved up to the four-cell embryo stage an d then gradually disappeared. In F1 hybrid animals, genome separation was a lso observed in a proportion of somatic cells. Separate nuclear compartment s during preimplantation development, when extreme chroma tin remodelling o ccurs, and possibly in some differentiated cell types, may be associated wi th epigenetic reprogramming.