AUTHOR=Olivier-Van Stichelen Stéphanie , Hanover John A. 

TITLE=X-inactivation normalizes O-GlcNAc transferase levels and generates an O-GlcNAc-depleted Barr body

JOURNAL=Frontiers in Genetics

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2014.00256

DOI=10.3389/fgene.2014.00256

ISSN=1664-8021

ABSTRACT=<p><italic>O</italic>-GlcNAc Transferase (OGT) catalyzes protein <italic>O</italic>-GlcNAcylation, an abundant and dynamic nuclear and cytosolic modification linked to epigenetic regulation of gene expression. The steady-state levels of <italic>O</italic>-GlcNAc are influenced by extracellular glucose concentrations suggesting that <italic>O</italic>-GlcNAcylation may serve as a metabolic sensor. Intriguingly, human <italic>OGT</italic> is located on the X-chromosome (Xq13) close to the X-inactivation center (XIC), suggesting that <italic>OGT</italic> levels may be controlled by dosage compensation. In human female cells, dosage compensation is accomplished by X-inactivation. Long noncoding RNAs and polycomb repression act together to produce an inactive X chromosome, or Barr body. Given that OGT has an established role in polycomb repression, it is uniquely poised to auto-regulate its own expression through X-inactivation. In this study, we examined <italic>OGT</italic> expression in male, female and triple-X female human fibroblasts, which differ in the number of inactive X chromosomes (Xi). We demonstrate that <italic>OGT</italic> is subjected to random X-inactivation in normal female and triple X cells to regulate <italic>OGT</italic> RNA levels. In addition, we used chromatin isolation by RNA purification (ChIRP) and immunolocalization to examine <italic>O</italic>-GlcNAc levels in the Xi/Barr body. Despite the established role of <italic>O</italic>-GlcNAc in polycomb repression, OGT and target proteins bearing <italic>O</italic>-GlcNAc are largely depleted from the highly condensed Barr body. Thus, while <italic>O</italic>-GlcNAc is abundantly present elsewhere in the nucleus, its absence from the Barr body suggests that the transcriptional quiescence of the Xi does not require OGT or <italic>O</italic>-GlcNAc.</p>