Mouse Xist expression begins at zygotic genome activation and is timed by a zygotic clock

Citations Over TimeTop 11% of 2001 papers

Abstract

The imprinted mouse Xist (X-inactive specific transcript) gene is involved in the initiation of X-chromosome inactivation. Only the paternal Xist is expressed in preimplantation development beginning from the 4-cell stage, preceding and in correlation with paternal X-inactivation in the extraembryonic lineage of the blastocyst. To better understand the mechanisms regulating Xist expression in early development, we investigated the precise timing of its onset. We set up a single-cell RT-PCR for the simultaneous analysis on single embryos of Xist and Hprt (internal control) cDNAs and a Y-chromosome specific DNA sequence, Zfy (for embryo sexing). Applying this procedure, we demonstrate 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). We then examined, if Xist expression at the 2-cell stage is dependent on the lapse of time spent since fertilization, as previously reported for zygotic genes. One-cell embryos at the G2-phase of the first cell-cycle were cultured with cytochalasin D (inhibitor of cytokinesis but not of DNA synthesis or nuclear progression) for a time equivalent to the 4-cell stage in control, untreated embryos. We show that Xist activation occurs at a scheduled time following fertilization despite the embryos being blocked at the 1-cell stage, suggesting the existence of a zygotic clock involved in the regulation of the transcription of this imprinted gene.

Related Papers

• → A promoter mutation in the XIST gene in two unrelated families with skewed X-chromosome inactivation(1997)295 cited
• → Xist has properties of the X-chromosome inactivation centre(1997)250 cited
• → Expression of the X–inactivation–associated gene XIST during spermatogenesis(1992)140 cited
• → A male with two contiguous inactivation centers on a single X chromosome: study of X inactivation and XIST expression(1992)20 cited
• → Xist and X chromosome inactivation(1998)14 cited