Highly restricted localization of RNA polymerase II within a locus control region of a tissue-specific chromatin domain

RNA polymerase II (Pol II) can associate with regulatory elements far from promoters. For the murine β-globin locus, Pol II binds the β-globin locus control region (LCR) far upstream of the β-globin promoters, independent of recruitment to and activation of the βmajor promoter. We describe here an analysis of where Pol II resides within the LCR, how it is recruited to the LCR, and the functional consequences of recruitment. High-resolution analysis of the distribution of Pol II revealed that Pol II binding within the LCR is restricted to the hypersensitive sites. Blocking elongation eliminated the synthesis of genic and extragenic transcripts and eliminated Pol II from the βmajor open reading frame. However, the elongation blockade did not redistribute Pol II at the hypersensitive sites, suggesting that Pol II is recruited to these sites. The distribution of Pol II did not strictly correlate with the distributions of histone acetylation and methylation. As Pol II associates with histone-modifying enzymes, Pol II tracking might be critical for establishing and maintaining broad histone modification patterns. However, blocking elongation did not disrupt the histone modification pattern of the β-globin locus, indicating that Pol II tracking is not required to maintain the pattern

Dynamic Regulation of Histone H3 Methylated at Lysine 79 within a Tissue-specific Chromatin Domain

Post-translational modifications of individual lysine residues of core histones can exert unique functional consequences. For example, methylation of histone H3 at lysine 79 (H3-meK79) has been implicated recently in gene silencing in Saccharomyces cerevisiae. However, the distribution and function of H3-meK79 in mammalian chromatin are not known. We found that H3-meK79 has a variable distribution within the murine beta-globin locus in adult erythroid cells, being preferentially enriched at the active betamajor gene. By contrast, acetylated H3 and H4 and H3 methylated at lysine 4 were enriched both at betamajor and at the upstream locus control region. H3-meK79 was also enriched at the active cad gene, whereas the transcriptionally inactive loci necdin and MyoD1 contained very little H3-meK79. As the pattern of H3-meK79 at the beta-globin locus differed between adult and embryonic erythroid cells, establishment and/or maintenance of H3-meK79 was developmentally dynamic. Genetic complementation analysis in null cells lacking the erythroid and megakaryocyte-specific transcription factor p45/NF-E2 showed that p45/NF-E2 preferentially establishes H3-meK79 at the betamajor promoter. These results support a model in which H3-meK79 is strongly enriched in mammalian chromatin at active genes but not uniformly throughout active chromatin domains. As H3-meK79 is highly regulated at the beta-globin locus, we propose that the murine ortholog of Disruptor of Telomeric Silencing-1-like (mDOT1L) methyltransferase, which synthesizes H3-meK79, regulates beta-globin transcription

Clonal hematopoiesis is associated with risk of severe Covid-19.

Acquired somatic mutations in hematopoietic stem and progenitor cells (clonal hematopoiesis or CH) are associated with advanced age, increased risk of cardiovascular and malignant diseases, and decreased overall survival. These adverse sequelae may be mediated by altered inflammatory profiles observed in patients with CH. A pro-inflammatory immunologic profile is also associated with worse outcomes of certain infections, including SARS-CoV-2 and its associated disease Covid-19. Whether CH predisposes to severe Covid-19 or other infections is unknown. Among 525 individuals with Covid-19 from Memorial Sloan Kettering (MSK) and the Korean Clonal Hematopoiesis (KoCH) consortia, we show that CH is associated with severe Covid-19 outcomes (OR = 1.85, 95%=1.15-2.99, p = 0.01), in particular CH characterized by non-cancer driver mutations (OR = 2.01, 95% CI = 1.15-3.50, p = 0.01). We further explore the relationship between CH and risk of other infections in 14,211 solid tumor patients at MSK. CH is significantly associated with risk of Clostridium Difficile (HR = 2.01, 95% CI: 1.22-3.30, p = 6×10-3) and Streptococcus/Enterococcus infections (HR = 1.56, 95% CI = 1.15-2.13, p = 5×10-3). These findings suggest a relationship between CH and risk of severe infections that warrants further investigation