En bloc and segmental deletions of human XIST reveal X chromosome inactivation-involving RNA elements

Area of Science:

• Genetics
• Epigenetics
• Molecular Biology

Background:

• XIST RNA initiates X chromosome inactivation (XCI) in female cells.
• The precise mechanisms and functional domains of human XIST RNA in XCI are not fully understood.
• Understanding human XIST RNA is crucial for deciphering female cell development and gene regulation.

Purpose of the Study:

• To systematically identify functional elements within human XIST RNA essential for XCI.
• To compare the functional domains of human XIST RNA with its mouse counterpart, Xist.
• To elucidate the unique structural and functional characteristics of human XIST RNA.

Main Methods:

• Utilized CRISPR-Cas9 technology for high-efficiency homozygous deletion of 11 XIST RNA segments and the entire gene in K562 cells.
• Employed high-throughput RNA sequencing to analyze gene expression changes post-deletion.
• Conducted RNA fluorescence in situ hybridization to visualize XIST RNA localization and function.

Main Results:

• Homozygous deletions of the entire XIST gene or its promoter reactivated the inactive X chromosome, indicated by global up-regulation of X-linked genes.
• Segmental deletion analyses revealed that exon 5, containing a non-repeat element, is critical for maintaining XCI.
• Exons 2, 3, 4, and repeat regions in exon 1 were found to be less critical for XCI maintenance, contrasting with mouse Xist RNA.

Conclusions:

• The study successfully dissected the functional domains of human XIST RNA using Cas9-assisted deletions.
• Exon 5 plays a key role in maintaining XCI in human cells, highlighting unique functional domains compared to mouse Xist.
• This research provides novel insights into the specific mechanisms of XCI mediated by human XIST RNA.