Deciphering 3D Organization of Chromosomes Using Hi-C Data

HU promotes higher order chromosome organization and influences DNA replication rates in Streptococcus pneumoniae

Nucleoid-associated proteins (NAPs) are crucial for maintaining chromosomal compaction and architecture, and are actively involved in DNA replication, recombination, repair, and gene regulation. In Streptococcus pneumoniae, the role of the highly conserved NAP HU in chromosome conformation has not yet been investigated. Here, we use a multi-scale approach to explore HU's role in chromosome conformation and segregation dynamics. By combining superresolution microscopy and whole-genome-binding analysis, we describe the nucleoid as a dynamic structure where HU binds transiently across the entire nucleoid, with a preference for the origin of replication over the terminus. Reducing cellular HU levels impacts nucleoid maintenance and disrupts nucleoid scaling with cell size, similar to the distortion caused by fluoroquinolones, supporting its requirement for maintaining DNA supercoiling. Furthermore, in cells lacking HU, the replication machinery is misplaced, preventing cells from initiating and proceeding with ongoing replication. Chromosome conformation capture coupled to deep sequencing (Hi-C) revealed that HU is required to maintain cohesion between the two chromosomal arms, similar to the structural maintenance of chromosome complex. Together, we show that by promoting long-range chromosome interactions and supporting the architecture of the domain encompassing the origin, HU is essential for chromosome integrity and the intimately related processes of replication and segregation.

The SNP of rs6854845 suppresses transcription via the DNA looping structure alteration of super-enhancer in colon cells

Single-nucleotide polymorphisms (SNPs) identified by Genome-Wide Association Studies (GWASs) have been determined to closely connect with multiple diseases. Previous studies revealed one underlying mechanism that SNPs located within the regulatory elements could affect the encoding gene expression through long-range regulation. SNP rs6854845 was suggested to be a risk of colon cancer in human population. Nevertheless, the underlying molecular mechanism for colon carcinogenesis remains largely unknown. In present study, rs6854845 with G > T mutation in situ in FHC, HCT-116 and SW-480 cells were generated by Crispr/Cas9. The nearby chromatin organization was investigated by chromatin conformation capture (3C). And the expression of coding gene regulated by super-enhancer (SE) was detected by real-time PCR. We observed a significantly different pattern of the genome organization upon rs6854845 generation in colon epithelial cells but not in colon cancer cells. Moreover, we observed the shifted enrichment of H3K4me1 and H3K27ac at the SE (chr4:75.7M-76.0 M) where rs6854845 located. Furthermore, we observed that the transcription of the gene clusters regulated by SE were affected by rs6854845 in colon cells. Overall, our results demonstrated that SNP rs6854845 located in SE could destroy the long-range chromosomal interaction between SE and target gene clusters thereby affecting the transcription of these genes.

The effect of CTCF binding sites destruction by CRISPR/Cas9 on transcription of metallothionein gene family in liver hepatocellular carcinoma

Chromatin spatial organization is essential for transcriptional modulation and stabilization. The pattern of DNA distal interplay form the multiple topological associating domains (TADs), and further assemble the functional compartmentalization with open and expression-active chromatin ("A" compartments) or closed and expression-inactive chromatin ("B" compartments) in genome, whose boundaries were defined by the high enrichment of CCCTC-binding factor (CTCF). Nevertheless, As a potential therapeutic strategy, changing the local chromatin architecture via adding or removing the CTCF binding sites in situ to regulate the transcription activity of genes within one TAD in cancer cells is poorly explored. In present study, we observed that the metallothionein (MT) family were all remarkably decreased in HCC of TCGA database, and MT genes family were located within a TAD of 1.2 Mb at 16q13 in order, and CTCF binding sites were distributed at the both sites of MT gene clusters. Furthermore, CRISPR/Cas9 was employed to destroy the CTCF binding sites at the vicinity of the MT family in human liver hepatocellular carcinoma (HCC) cell lines Huh-7 and HepG2. And the presence of up-regulated transcription of MTs were observed in Huh-7 and HepG2 cells compared to normal liver CRL-12461 cells. Moreover, the presence of the varying DNA interplay as well as H3K4me3 and H3K9me3 modification on different MT genes were observed after CTCF binding domain destruction compared to the control using chromosome conformation capture (3C) and chromatin immunoprecipitation (ChIP). Our results determined a potential way to regulate the transcription of a series of genes via changing the local genomic organization for diseases treatment.