Mouse Xist Expression Begins at Zygotic Genome Activation and Is Timed by a Zygotic Clock

Maurizio Zuccotti, Michele Boiani, Ruben Ponce, Stefano Guizzardi, Renato Scandroglio, Silvia Garagna, Carlo Alberto Redi

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)14-20
Number of pages7
JournalMolecular Reproduction and Development
Issue number1
Publication statusPublished - Jan 2002


  • Gene expression
  • Genomic imprinting
  • Preimplantation development
  • X-inactivation

ASJC Scopus subject areas

  • Cell Biology
  • Developmental Biology
  • Genetics


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