Paternal DNA strands segregate to both trophectoderm and inner cell mass of the developing mouse embryo.

The localization of sperm DNA strands was examined in preimplantation mouse embryos. Male mice were treated with bromodeoxyuridine (BrdU) to label germ-cell-line DNA and were then mated with unlabeled females. Sperm DNA strands in early embryos derived from these matings could be detected by means of a fluorescent antibody specific to BrdU. The position and number of fluorescent spots detected in the developing embryos are consistent with a model in which paternal DNA strands segregate at random into both the trophectoderm and the inner cell mass. Although we could not follow the segregation of individual paternal chromosomes, we could detect no overall segregation pattern of the sperm DNA strands that could be obviously related to chromosome imprinting.