%A Olivier-Van Stichelen,Stéphanie %A Hanover,John A. %D 2014 %J Frontiers in Genetics %C %F %G English %K O-GlcNAcylation,barr body,X-chromosome inactivation,O-GlcNAc transferase,Gene Silencing %Q %R 10.3389/fgene.2014.00256 %W %L %M %P %7 %8 2014-August-04 %9 Original Research %+ Dr John A. Hanover,jah@helix.nih.gov %# %! X-inactivation and O-GlcNAc cycling %* %< %T X-inactivation normalizes O-GlcNAc transferase levels and generates an O-GlcNAc-depleted Barr body %U https://www.frontiersin.org/articles/10.3389/fgene.2014.00256 %V 5 %0 JOURNAL ARTICLE %@ 1664-8021 %X O-GlcNAc Transferase (OGT) catalyzes protein O-GlcNAcylation, an abundant and dynamic nuclear and cytosolic modification linked to epigenetic regulation of gene expression. The steady-state levels of O-GlcNAc are influenced by extracellular glucose concentrations suggesting that O-GlcNAcylation may serve as a metabolic sensor. Intriguingly, human OGT is located on the X-chromosome (Xq13) close to the X-inactivation center (XIC), suggesting that OGT 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 OGT expression in male, female and triple-X female human fibroblasts, which differ in the number of inactive X chromosomes (Xi). We demonstrate that OGT is subjected to random X-inactivation in normal female and triple X cells to regulate OGT RNA levels. In addition, we used chromatin isolation by RNA purification (ChIRP) and immunolocalization to examine O-GlcNAc levels in the Xi/Barr body. Despite the established role of O-GlcNAc in polycomb repression, OGT and target proteins bearing O-GlcNAc are largely depleted from the highly condensed Barr body. Thus, while O-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 O-GlcNAc.