A Conserved Noncoding Locus Regulates Random Monoallelic Xist Expression across a Topological Boundary

Area of Science:

• Genetics
• Developmental Biology
• Epigenetics

Background:

• Topologically associating domains (TADs) spatially partition the genome, restricting cis-regulatory communication crucial for mammalian development.
• The Xist locus plays a central role in X chromosome inactivation, a key developmental process.

Purpose of the Study:

• To investigate the regulatory mechanisms of Xist and their relationship with TADs.
• To identify novel cis-regulatory elements involved in X chromosome inactivation.

Main Methods:

• Analysis of the Xist locus and its regulatory sequences.
• Investigating the function of the Linx promoter (LinxP) in X chromosome inactivation.
• Comparative analysis of LinxP conservation across mammals.

Main Results:

• The Linx promoter (LinxP) acts as a long-range silencer for the Xist locus, influencing X chromosome inactivation.
• This silencing effect is independent of Linx transcription and the Tsix regulator.
• LinxP is conserved across mammals, suggesting an ancient regulatory role.
• Relocating LinxP into the same TAD as Xist changes its function from silencer to enhancer.

Conclusions:

• A novel regulatory axis involving LinxP modulates X chromosome inactivation.
• cis-regulatory elements can exert effects across TAD boundaries, influencing developmental decisions.
• TAD partitioning may be exploited to control gene expression and developmental pathways.