A maternal factor affecting mouse blastocyst formation.

Normal development of the mouse embryo requires the presence of both paternal and maternal genomes. This is due to functional differences having their origin in a differential imprinting of parental genomes. Furthermore, several lines of evidence show that the very early interactions between egg cytoplasm and pronuclei may influence the programming of the embryonic genome and modulate the functional inequality of the parental contribution even during preimplantation stages. In this paper, we show that a factor present in ovulated oocytes of the mouse mutant strain DDK and therefore of maternal origin prevents the formation of the blastocyst. This factor, which acts via an interaction with the paternal genome, is present in oocytes as an RNA and is still active in preimplantation embryos. This is the first direct evidence of such a maternal control in the mouse.