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Impact of somatic XIST deletions on ongoing XIST expression and inactive X silencing and heterochromatin

Karanveer S Bhangu1, Christine Yang1, Hannah J Illing1

  • 1Department of Medical Genetics, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC Canada V6T 1Z3.

Human Molecular Genetics
|October 23, 2025
PubMed

Insights

Loss of the long non-coding RNA XIST in somatic cells upregulates X-linked escape genes. XIST

Area of Science:

  • Epigenetics
  • Genomics
  • Molecular Biology

Background:

  • The long non-coding RNA XIST is essential for X-chromosome inactivation.
  • XIST expression persists in somatic cells, but its role in maintaining gene silencing is not fully understood.
  • Altered XIST expression is linked to aging and cancer.

Purpose of the Study:

  • To investigate the effects of complete or partial XIST loss on gene expression and chromatin structure.
  • To identify specific XIST regulatory elements and their impact on gene silencing.
  • To explore the interplay between XIST and other epigenetic silencing pathways.

Main Methods:

  • Utilized the hTERT RPE-1 cell line for experiments.
  • Generated cell lines with complete XIST loss, partial XIST reduction (F-repeat deletion), and XIST delocalization (E-repeat deletion).
  • Analyzed gene expression changes, particularly for X-linked genes and escape genes.
  • Assessed alterations in histone modifications like H3K27me3, H2AK119ub, and H3K9me3.

Main Results:

  • Complete XIST loss led to significant upregulation of X-linked escape genes (average 20% increase).
  • MED14 and USP9X showed near-complete reactivation upon XIST loss.
  • Partial XIST loss or delocalization resulted in partial gene reactivation.
  • XIST loss correlated with decreased H3K27me3 and H2AK119ub, but inhibiting these alone did not fully restore gene expression.
  • H3K9me3 reduction partially reactivated USP9X, suggesting combinatorial epigenetic regulation.

Conclusions:

  • XIST expression and localization in somatic cells actively suppress the expression of X-linked escape genes.
  • Epigenetic silencing pathways, including H3K27me3, H2AK119ub, and H3K9me3, act combinatorially with XIST to maintain X-chromosome inactivation.
  • Understanding XIST's role is crucial for studying gene regulation in aging and cancer.
Keywords:
X-chromosome inactivationXIST lncRNAXIST-dependent silencingescapeeheterochromatin

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