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Live-cell chromosome dynamics and outcome of X chromosome pairing events during ES cell differentiation

Osamu Masui1, Isabelle Bonnet, Patricia Le Baccon

  • 1Institut Curie, Paris, France.

Cell
|May 3, 2011
PubMed

Insights

Symmetry-breaking in early ES cell differentiation involves X chromosome pairing. This dynamic process facilitates monoallelic regulation of Xist RNA, crucial for random X inactivation in female mammals.

Area of Science:

  • Epigenetics and Gene Regulation
  • Mammalian Embryonic Stem Cell Biology
  • Chromosomal Dynamics

Background:

  • Random X inactivation is a key process for dosage compensation in female mammals.
  • Monoallelic regulation of Xist RNA expression is essential for initiating X inactivation.
  • The role of homologous chromosome pairing in Tsix/Xite regulation has been hypothesized but not directly observed.

Purpose of the Study:

  • To investigate the live-cell dynamics of X chromosome pairing during mouse embryonic stem cell differentiation.
  • To determine the functional outcome of Tsix pairing on Tsix/Xite expression and Xist RNA regulation.
  • To elucidate the spatiotemporal choreography of X chromosomes in early differentiation.

Main Methods:

  • Live-cell imaging of differentiating mouse embryonic stem cells.
  • Tracking of Xic loci dynamics during homologous chromosome pairing.
  • Analysis of Tsix expression patterns in relation to Xic locus movements.

Main Results:

  • Genome dynamics, including Xic loci, increase during early differentiation.
  • Xic loci exhibit reduced movement during homologous pairing events.
  • Separation of paired Xic loci leads to transient monoallelic Tsix expression, enabling Xist upregulation.

Conclusions:

  • Homologous X chromosome pairing plays a direct role in breaking symmetry during early differentiation.
  • Pairing dynamics facilitate the monoallelic regulation of Tsix/Xite, a prerequisite for random X inactivation.
  • The study reveals the spatiotemporal coordination of X chromosomes essential for initiating monoallelic gene expression.

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