Summary In mammals, DNA methylation is essential for protecting repetitive sequences from aberrant transcription and recombination. In some developmental contexts (e.g., preimplantation embryos) DNA is hypomethylated but repetitive elements are not dysregulated, suggesting that alternative protection mechanisms exist. Here we explore the processes involved by investigating the role of the chromatin factors DAXX and ATRX. Using genome-wide binding and transcriptome analysis, we found that DAXX and ATRX have distinct chromatin-binding profiles and are co-enriched at tandem repetitive elements in wildtype mouse ESCs. Global DNA hypomethylation further promoted recruitment of the DAXX/ATRX complex to tandem repeat sequences, including retrotransposons and telomeres. Knockdown of DAXX/ATRX in cells with hypomethylated genomes exacerbated aberrant transcriptional de-repression of repeat elements and telomere dysfunction. Mechanistically, DAXX/ATRX-mediated repression seems to involve SUV39H recruitment and H3K9 trimethylation. Our data therefore suggest that DAXX and ATRX safeguard the genome by silencing repetitive elements when DNA methylation levels are low.

In mammals, maintenance of the linear chromosome ends (or telomeres) involves faithful replication of genetic materials and protection against DNA damage signals, to ensure genome stability and integrity. These tasks are carried out by the telomerase holoenzyme and a unique nucleoprotein structure in which an array of telomere-associated proteins bind to telomeric DNA to form special protein/DNA complexes. The telomerase complex, which is comprised of telomeric reverse transcriptase (TERT), telomeric RNA component (TERC), and other assistant factors, is responsible for adding telomeric repeats to the ends of chromosomes. Without proper telomere maintenance, telomere length will shorten with successive round of DNA replication due to the so-called end replication problem. Aberrant regulation of telomeric proteins and/or telomerase may lead to abnormalities that can result in diseases such as dyskeratosis congenita (DC) and cancers. Understanding the mechanisms that regulate telomere homeostasis and the factors that contribute to telomere dysfunction should aid us in developing diagnostic and therapeutic tools for these diseases.

Background: Ogt N-acetylglucosylates proteins and plays an important role in mouse ES cells. Results: The DNA demethylation enzyme Tet1 interacts with Ogt and is O-GlcNAcylated. Conclusion: Tet1 protein stability is positively regulated by O-GlcNAcylation, and its repression function on targeting genes is dependent on Ogt. Significance: Ogt-Tet1 interaction should further our understanding of how O-GlcNAcylation is integrated into ES cell regulatory networks.

BackgroundRenal endothelial cells from glomerular, cortical, and medullary kidney compartments are exposed to different microenvironmental conditions and support specific kidney processes. However, the heterogeneous phenotypes of these cells remain incompletely inventoried. Osmotic homeostasis is vitally important for regulating cell volume and function, and in mammals, osmotic equilibrium is regulated through the countercurrent system in the renal medulla, where water exchange through endothelium occurs against an osmotic pressure gradient. Dehydration exposes medullary renal endothelial cells to extreme hyperosmolarity, and how these cells adapt to and survive in this hypertonic milieu is unknown.MethodsWe inventoried renal endothelial cell heterogeneity by single-cell RNA sequencing >40,000 mouse renal endothelial cells, and studied transcriptome changes during osmotic adaptation upon water deprivation. We validated our findings by immunostaining and functionally by targeting oxidative phosphorylation in a hyperosmolarity model in vitro and in dehydrated mice in vivo.ResultsWe identified 24 renal endothelial cell phenotypes (of which eight were novel), highlighting extensive heterogeneity of these cells between and within the cortex, glomeruli, and medulla. In response to dehydration and hypertonicity, medullary renal endothelial cells upregulated the expression of genes involved in the hypoxia response, glycolysis, and—surprisingly—oxidative phosphorylation. Endothelial cells increased oxygen consumption when exposed to hyperosmolarity, whereas blocking oxidative phosphorylation compromised endothelial cell viability during hyperosmotic stress and impaired urine concentration during dehydration.ConclusionsThis study provides a high-resolution atlas of the renal endothelium and highlights extensive renal endothelial cell phenotypic heterogeneity, as well as a previously unrecognized role of oxidative phosphorylation in the metabolic adaptation of medullary renal endothelial cells to water deprivation.

SUMMARY Biomarkers for predicting prognosis are critical to treating colorectal cancer (CRC) patients. We found that CSN6, a subunit of COP9 signalosome, is overexpressed in CRC samples and that CSN6 overexpression is correlated with poor patient survival. Mechanistic studies revealed that CSN6 is deregulated by EGFR signaling, in which ERK2 binds directly to CSN6 Leu163/Val165 and phosphorylates CSN6 at Ser148. Furthermore, CSN6 regulated β-Trcp and stabilizes β-catenin expression by blocking the ubiquitin-proteasome pathway, thereby promoting CRC development. High CSN6 expression was positively correlated with ERK2 activation and β-catenin overexpression in CRC samples, and inhibiting CSN6 stability with cetuximab reduced colon cancer growth. Taken together, our study’s findings indicate that the deregulation of β-catenin by ERK2-activated CSN6 is important for CRC development.