d Department of Pharmaceutical Sciences , College of Pharmacy, University of New England, Portland , ME , USA.
Published: March 2017
AI Article Synopsis
Article Abstract
Cell differentiation is associated with changes in chromatin organization and gene expression. In this study, we examine chromatin structure following differentiation of the human myeloid leukemia cell line (HL-60/S4) into granulocytes with retinoic acid (RA) or into macrophage with phorbol ester (TPA). We performed ChIP-seq of histone H3 and its modifications, analyzing changes in nucleosome occupancy, nucleosome repeat length, eu-/heterochromatin redistribution and properties of epichromatin (surface chromatin adjacent to the nuclear envelope). Nucleosome positions changed genome-wide, exhibiting a specific class of alterations involving nucleosome loss in extended (∼1kb) regions, pronounced in enhancers and promoters. Genes that lost nucleosomes at their promoters showed a tendency to be upregulated. On the other hand, nucleosome gain did not show simple effects on transcript levels. The average genome-wide nucleosome repeat length (NRL) did not change significantly with differentiation. However, we detected an approximate 10 bp NRL decrease around the haematopoietic transcription factor (TF) PU.1 and the architectural protein CTCF, suggesting an effect on NRL proximal to TF binding sites. Nucleosome occupancy changed in regions associated with active promoters in differentiated cells, compared with untreated HL-60/S4 cells. Epichromatin regions revealed an increased GC content and high nucleosome density compared with surrounding chromatin. Epichromatin showed depletion of major histone modifications and revealed enrichment with PML body-associated genes. In general, chromatin changes during HL-60/S4 differentiation appeared to be more localized to regulatory regions, compared with genome-wide changes among diverse cell types studied elsewhere.
Sulfonium is an electrophilic and biocompatible group that is widely applied in synthetic chemistry on small molecules. However, there have been few developments of peptide or protein-based sulfonium tools. We recently reported sulfonium-mediated tryptophan crosslinking and developed NleSme2 (norleucine-dimethylsulfonium) peptides as dimethyllysine mimics that crosslink site-specific methyllysine readers.
CHD6, a member of the chromodomain helicase DNA-binding protein family, has been implicated in various diseases and tumors. However, its precise binding model of CHD6 on regulatory functional genes remains poorly understood. In this study, we discovered sharp peaks of CHD6, as the first member of CHD family for housekeeping process, binding only to the promoter region of genes in the C4-2 cell line.
8-oxoguanine (8-oxoG) is a common oxidative DNA lesion that causes G > T substitutions. Determinants of local and regional differences in 8-oxoG-induced mutability across genomes are currently unknown. Here, we show DNA oxidation induces G > T substitutions and insertion/deletion (INDEL) mutations in human cells and cancers.
In this article I review mechanisms that underpin epigenetic inheritance of CpG methylation and histone H3 lysine 9 methylation (H3K9me) in chromatin in fungi and mammals. CpG methylation can be faithfully inherited epigenetically at some sites for a lifetime in vertebrates and, remarkably, can be propagated for millions of years in some fungal lineages. Transmission of methylation patterns requires maintenance-type DNA methyltransferases (DNMTs) that recognize hemimethylated CpG DNA produced by replication.
A major challenge in epigenetics is uncovering the dynamic distribution of nucleosomes and other DNA-binding proteins, which plays a crucial role in regulating cellular functions. Established approaches such as ATAC-seq, ChIP-seq, and CUT&RUN provide valuable insights but are limited by the ensemble nature of their data, masking the cellular and molecular heterogeneity that is often functionally significant. Recently, long-read sequencing technologies, particularly Single Molecule, Real-Time (SMRT/PacBio) sequencing, have introduced transformative capabilities, such as N6-methyladenine (6mA) footprinting.
