We are studying the profile of relative abundance of zygotic gene transcripts throughout preimplantation development.

We have recently described the pattern of expression of the Xist gene (Zuccotti et al., 2002), showing that Xist expression begins at the G2-phase of 2-cell female embryos, earlier than previously reported and at the same time of the major wave of zygotic genome activation (ZGA). Also, we have shown that Xist activation occurs at a scheduled time following fertilization, suggesting the existence of a zygotic clock involved in the regulation of the transcription of this imprinted gene.