FACT, in addition to its role in transcription, is likely implicated in both transcription-coupled nucleotide excision repair and DNA double strand break repair. Here, we present evidence that FACT could be directly involved in Base Excision Repair and elucidate the chromatin remodeling mechanisms of FACT during BER. We found that, upon oxidative stress, FACT is released from transcription related protein complexes to get associated with repair proteins and chromatin remodelers from the SWI/SNF family. We also showed the rapid recruitment of FACT to the site of damage, coincident with the glycosylase OGG1, upon the local generation of oxidized DNA. Interestingly, FACT facilitates uracil-DNA glycosylase in the removal of uracil from nucleosomal DNA thanks to an enhancement in the remodeling activity of RSC. This discloses a novel property of FACT wherein it has a co-remodeling activity and strongly enhances the remodeling capacity of the chromatin remodelers. Altogether, our data suggest that FACT may acts in concert with RSC to facilitate excision of DNA lesions during the initial step of BER. In the nucleus, DNA is packaged into chromatin. The repeating unit of chromatin, the nucleosome, consists of a histone octamer around which DNA is wrapped into two superhelical turns. The nucleosome is a barrier for various nuclear processes which require access to DNA. To repair lesions on DNA, this barrier has to be overcome by either nucleosome remodeling or by histone eviction. Here we present evidence that FACT, a protein known to be involved in transcription, is also involved in BER, by boosting nucleosome remodeling. Upon in vivo oxidized DNA lesion induction, FACT exhibits a BER-like protein behavior, and it is recruited to the sites of DNA damages. In vitro experiments show that FACT boosts the remodeling activity of the chromatin remodeler RSC and is implicated in DNA repair. The presence of FACT greatly facilitates the removal of uracil from nucleosomal, but not from naked DNA, in a RSC-mediated reaction. Taken collectively, our in vitro and in vivo data reveal a role of FACT in BER by helping the remodeling of chromatin at the sites of lesions.

The epithelial-to-mesenchymal transition (EMT) is a physiological process activated during early embryogenesis, which continues to shape tissues and organs later on. It is also hijacked by tumor cells during metastasis. The regulation of EMT has been the focus of many research groups culminating in the last few years and resulting in an elaborate transcriptional network buildup. However, the implication of epigenetic factors in the control of EMT is still in its infancy. Recent discoveries pointed out that histone variants, which are key epigenetic players, appear to be involved in EMT control. This review summarizes the available data on histone variants’ function in EMT that would contribute to a better understanding of EMT itself and EMT-related diseases.

The linker histone H1 C‐terminal domain (CTD) plays a pivotal role in chromatin condensation. De novo frameshift mutations within the CTD coding region of H1.4 have recently been reported to be associated with Rahman syndrome, a neurological disease that causes intellectual disability and overgrowth. To investigate the mechanisms and pathogenesis of Rahman syndrome, we developed a cellular model using murine embryonic stem cells (mESCs) and CRISPR/Cas9 genome engineering. Our engineered mES cells facilitate detailed investigations, such as H1‐4 dynamics, immunoprecipitation, and nuclear localization; in addition, we tagged the mutant H1‐4 with a photoactivatable GFP (PA‐GFP) and an HA tag to facilitate pulldown assays. We anticipate that these engineered cells could also be used for the development of a mouse model to study the in vivo role of the H1‐4 protein.

Rahman syndrome is a rare developmental disorder caused by frameshift mutations in linker histone H1.4 that produce a truncated carboxy-terminal domain with reduced positive charge. We investigated the effects of a disease-associated mutation on chromatin structure and dynamics, focusing on H1.4-bound nucleosomes and hexanucleosomal arrays. We report that this mutation induces a more extended and flexible array conformation, characterized by enhanced linker DNA accessibility and an inability to form compact, regularly stacked nucleosome structures. Notably, mutant H1.4-bound arrays show a reduced capacity to undergo liquid-liquid and liquid-solid phase separation, closely resembling linker histone-free arrays. Molecular dynamics simulations corroborated by fluorescence resonance energy transfer measurements indicate that the mutated carboxy-terminal domain interacts with a shorter linker DNA segment, resulting in a more open nucleosome conformation. Consistent with these structural changes, the mutation significantly enhances H1.4 mobility within cell nuclei, reflecting a weaker chromatin association. The combined data suggest that Rahman syndrome-associated mutations promote an aberrantly relaxed chromatin state, potentially leading to the dysregulation of gene expression that may drive disease pathology. These findings underscore the essential role of the carboxy-terminal domain in chromatin compaction and provide mechanistic insights into the molecular etiology of Rahman syndrome.