Efficacy and safety are key objectives in generating high-quality pluripotent stem cells (PSCs). While naïve human PSCs (hPSCs) harbor an unstable genome limiting their broad applications, mouse embryonic stem cells (mESCs) uniquely exhibit both robust pluripotency and high genomic stability. Understanding whether and how these two attributes are co-regulated in mESCs could provide critical insights for producing safe and authentic hPSCs. Here, we reveal that the coordination of naïve pluripotency and genomic stability in mESCs is governed by a novel core pluripotency regulator, ZFP998. ZFP998 binds to promoters and enhancers of key ESC-identity genes, as well as to numerous DNA damage response and repair genes, thereby regulating their expression. Depletion of Zfp998 leads to the loss of naïve pluripotency and induces severe genomic instability. Conversely, overexpression of ZFP998 is sufficient to reprogram epiblast stem cells back to a naïve pluripotent state. Importantly, ectopic expression of ZFP998 in hESCs enhances both pluripotency and genomic stability. These findings suggest that this coupled regulatory mechanism is conserved in humans and provide a promising new strategy for generating safe, naïve hPSCs.

Maternal aging impairs embryo development. However, little is known regarding the molecular defects in aged human embryos. Combining single-cell RNA sequencing and ATAC-seq, we investigated aging-associated changes in the transcriptome and chromatin accessibility in fully grown GV oocytes, mature eggs, 4C, 8C, and morula embryos from young, middle-aged and old rhesus monkeys. We reveal that impaired maternal mRNA stability is a major RNA metabolism defect in aged oocytes. Unlike mice, aged monkey embryos display precocious expression of stage-specific genes including zygotic genome activation (ZGA) and morula-stage genes. Consistently, promoters and distal regulatory regions that show stage-specific accessibility changes in young embryos lose this dynamic regulation and become constitutively accessible in old embryos. Mechanistically, aged monkey embryos have reduced maternal transcripts of SETDB1 . Knockdown of SETDB1 in young monkey zygotes recapitulates aging-associated phenotypes. Thus, maternal SETDB1 insufficiency is a major factor contributing to developmental and molecular defects in aged embryos.

Long-term culture of human embryonic stem cells (hESCs) often induces chromosomal abnormalities, which limits their clinical use. However, the underlying mechanisms are unclear. Early replication fragile sites (ERFSs) are genomic loci susceptible to breakage in early S-phase and serve as hotspots for chromosomal rearrangements, with established links to carcinogenesis. To map ERFSs in hESCs, we established the early S-phase synchronization protocols and identified ERFSs. These ERFSs are enriched in GC content and short interspersed nuclear elements (SINEs) and are frequently located in promoters or enhancers of genes involved in pluripotency, proliferation, and genomic stability. ERFSs also overlap with regions associated with copy number variants (CNVs) and single nucleotide variants (SNVs) linked to cancers. Furthermore, we found that chromatin accessibility contributes to ERFS formation. Collectively, these findings provide a key resource for advancing ERFS research, offering insights into the phenotypic and genomic alterations observed in long-term hESC cultures.

Embryonic stem cells (ESCs) exhibit a hyperactive chromatin state at ribosomal RNA (rRNA) genes, which not only plays roles in active rRNA synthesis and ribosome biogenesis (RiBi), but also links to genome architecture. However, how this active chromatin state is maintained in ESCs remains poorly understood. Here, we identify Tcf15, a mouse ESC-specific factor, as a novel regulator of ribosomal DNA (rDNA) chromatin state. Tcf15 localizes to the nucleolus, binds the coding region of rRNA genes, and independently recruits epigenetic modifiers-either Tet2 or Rbbp5 (a core component of H3K4 methyltransferases)-to promote an active chromatin configuration. Depletion of Tcf15 increases DNA methylation and H3K27me3 levels at rDNA. Intriguingly, the Tcf15-Rbbp5 axis ensures precursor rRNA transcription and RiBi, whereas the Tcf15-Tet2 axis is not involved in rRNA synthesis. Ribosome profiling further revealed compromised translation of a subset of mRNAs involved in DNA replication, damage response, and repair. Consequently, Tcf15- or Rbbp5-deficient ESCs exhibit severe genomic instability. Our findings add a new regulatory layer of chromatin state in rDNA of stem cells, and reveal a previously unrecognized phenotypic consequence of defective RiBi in ESCs.

Type I-E CRISPR (clustered regularly interspaced short palindromic repeats)–Cas (CRISPR-associated proteins) system is one of the most extensively studied RNA-guided adaptive immune systems in prokaryotes, providing defense against foreign genetic elements. Unlike the previously characterized Cas3 nuclease, which exhibits progressive DNA cleavage in the typical type I-E system, a recently identified HNH-comprising Cascade system enables precise DNA cleavage. Here, we present several near-atomic cryo-electron microscopy (cryo-EM) structures of the Candidatus Cloacimonetes bacterium Cas5-HNH/Cascade complex, both in its DNA-bound and unbound states. Our analysis reveals extensive interactions between the HNH domain and adjacent subunits, including Cas6 and Cas11, with mutations in these key interactions significantly impairing enzymatic activity. Upon DNA binding, the Cas5-HNH/Cascade complex adopts a more compact conformation, with subunits converging toward the center of nuclease, leading to its activation. Notably, we also find that divalent ions such as zinc, cobalt, and nickel down-regulate enzyme activity by destabilizing the Cascade complex. Together, these findings offer structural insights into the assembly and activation of the Cas5-HNH/Cascade complex. Type I-E CRISPR–Cas system is one of the most extensively studied RNA-guided adaptive immune systems in prokaryotes. Here, The authors present structures of the Candidatus Cloacimonetes Cas5-HNH/Cascade, with insights into the assembly and activation of this complex.

The hierarchical packaging of chromatin fibers plays a critical role in gene regulation. The 30-nm chromatin fibers, a central-level structure bridging nucleosomal arrays to higher-order organizations, function as the first level of transcriptional dormant chromatin. The dynamics of 30-nm chromatin fiber play a crucial role in biological processes related to DNA. Here, we report a 3.6-angstrom resolution cryogenic electron microscopy structure of H5-bound dodecanucleosome, i.e., the chromatin fiber reconstituted in the presence of linker histone H5, which shows a two-start left-handed double helical structure twisted by tetranucleosomal units. An atomic structural model of the H5-bound chromatin fiber, including an intact chromatosome, is built, which provides structural details of the full-length linker histone H5, including its N-terminal domain and an HMG-motif-like C-terminal domain. The chromatosome structure shows that H5 binds the nucleosome off-dyad through a three-contact mode in the chromatin fiber. More importantly, the H5-chromatin structure provides a fine molecular basis for the intra-tetranucleosomal and inter-tetranucleosomal interactions. In addition, we systematically validated the physiological functions and structural characteristics of the tetranucleosomal unit through a series of genetic and genomic studies in Saccharomyces cerevisiae and in vitro biophysical experiments. Furthermore, our structure reveals that multiple structural asymmetries of histone tails confer a polarity to the chromatin fiber. These findings provide structural and mechanistic insights into how a nucleosomal array folds into a higher-order chromatin fiber with a polarity in vitro and in vivo.

Tree shrews ( Tupaia belangeri chinensis) share a close relationship to primates and have been widely used in biomedical research. We previously established a spermatogonial stem cell (SSC)-based gene editing platform to generate transgenic tree shrews. However, the influences of long-term expansion on tree shrew SSC spermatogenesis potential remain unclear. Here, we examined the in vivo spermatogenesis potential of tree shrew SSCs cultured across different passages. We found that SSCs lost spermatogenesis ability after long-term expansion (>50 passages), as indicated by the failure to colonize the seminiferous epithelium and generate donor spermatogonia (SPG)-derived spermatocytes or spermatids marking spermatogenesis. RNA sequencing (RNA-seq) analysis of undifferentiated SPGs across different passages revealed significant gene expression changes after sub-culturing primary SPG lines for more than 40 passages on feeder layers. Specifically, DNA damage response and repair genes (e.g., MRE11, SMC3, BLM, and GEN1) were down-regulated, whereas genes associated with mitochondrial function (e.g., NDUFA9, NDUFA8, NDUFA13, and NDUFB8) were up-regulated after expansion. The DNA damage accumulation and mitochondrial dysfunction were experimentally validated in high-passage cells. Supplementation with nicotinamide adenine dinucleotide (NAD +) precursor nicotinamide riboside (NR) exhibited beneficial effects by reducing DNA damage accumulation and mitochondrial dysfunction in SPG elicited by long-term culture. Our research presents a comprehensive analysis of the genetic and physiological attributes critical for the sustained expansion of undifferentiated SSCs in tree shrews and proposes an effective strategy for extended in vitro maintenance.

Fork stability is key to genome DNA duplication and genetic integrity. Long non-coding RNAs (LncRNAs) may play vital roles in fork stabilization and chromatin remodeling. Existing techniques such as NCC-RNA sequencing are useful to identify LncRNAs on nascent chromatin DNA. However, there is still a lack of methods for LncRNAs purification directly from replicative forks, hindering a deep understanding of the functions of LncRNAs in fork regulation. Here, we provide a step-by-step protocol named iROND (isolate RNAs on nascent DNA). iROND was developed and modified from iPOND, a well-known method for purifying fork-associated proteins. iROND relies on click chemistry reaction of 5'-ethynyl-2'-deoxyuridine (EdU)-labeled forks and biotin. After streptavidin pull down, fork-associated LncRNAs and proteins are purified simultaneously. iROND is compatible with downstream RNA sequencing, qPCR confirmation, and immunoblotting. Integrated with functional methods such as RNA fluorescent in situ hybridization (RNA FISH) and DNA fiber assay, it is feasible to screen fork-binding LncRNAs in defined cell lines and explore their functions. In summary, we provide a purification pipeline of fork-associated LncRNAs. iROND is also useful for studying other types of fork-associated non-coding RNAs. Key features • Purify long non-coding RNAs (LncRNAs) directly from replication forks. • Connects to RNA sequencing for screening easily. • Allows testing various genotoxic stress responses. • Provides LncRNA candidate list for downstream functional research.

The stability of eukaryotic genomes relies on the faithful transmission of DNA sequences and the maintenance of chromatin states through DNA replication. Plant TONSOKU (TSK) and its animal ortholog TONSOKU-like (TONSL) act as readers for newly synthesized histones and preserve DNA integrity via facilitating DNA repair at post-replicative chromatin. However, whether TSK/TONSL regulate the maintenance of chromatin states remains elusive. Here, we show that TSK is dispensable for global histone and nucleosome accumulation but necessary for maintaining repressive chromatin modifications, including H3K9me2, H2A.W, H3K27me3, and DNA methylation. TSK physically interacts with H3K9 methyltransferases and Polycomb proteins. Moreover, TSK mutation strongly enhances defects in Polycomb pathway mutants. TSK is intended to only associate with nascent chromatin until it starts to mature. We propose that TSK ensures the preservation of chromatin states by supporting the recruitment of chromatin modifiers to post-replicative chromatin in a critical short window of time following DNA replication.

Genetic alterations are often acquired during prolonged propagation of pluripotent stem cells (PSCs). This ruins the stem cell quality and hampers their full applications. Understanding how PSCs maintain genomic integrity would provide the clues to overcome the hurdle. It has been known that embryonic stem cells (ESCs) utilize high-fidelity pathways to ensure genomic stability, but the underlying mechanisms remain largely elusive. Here, we show that many DNA damage response and repair genes display differential alternative splicing in mouse ESCs compared to differentiated cells. Particularly, Rev1 and Polq , two key genes for mutagenic translesion DNA synthesis (TLS) and microhomology-mediated end joining (MMEJ) repair pathways, respectively, display a significantly higher rate of cryptic exon (CE) inclusion in ESCs. The frequent CE inclusion disrupts the normal protein expressions of REV1 and POLθ, thereby suppressing the mutagenic TLS and MMEJ. Further, we identify an ESC-specific RNA binding protein DPPA5A which stimulates the CE inclusion in Rev1 and Polq . Depletion of DPPA5A in mouse ESCs decreased the CE inclusion of Rev1 and Polq , induced the protein expression, and stimulated the TLS and MMEJ activity. Enforced expression of DPPA5A in NIH3T3 cells displayed reverse effects. Mechanistically, we found that DPPA5A directly regulated CE splicing of Rev1 . DPPA5A associates with U2 small nuclear ribonucleoprotein of the spliceosome and binds to the GA-rich motif in the CE of Rev1 to promote CE inclusion. Thus, our study uncovers a mechanism to suppress mutagenic TLS and MMEJ pathways in ESCs.

Embryonic stem cells (ESCs) are superior to differentiated cells to maintain genome stability, but the underlying mechanisms remain largely elusive. R-loops are constantly formed during transcription and are inducers of DNA damage if not resolved. Here we report that mouse ESCs (mESCs) can efficiently prevent unscheduled R-loop formation, and a long noncoding RNA Lnc530 plays regulatory role. Lnc530 is expressed in mESCs and localizes on R-loops. Depletion of Lnc530 in mESCs causes R-loop accumulation and DNA damage, whereas forced expression of Lnc530 in differentiated cells suppresses the R-loop formation. Mechanistically, Lnc530 associates with DDX5 and TDP-43 in an inter-dependent manner on R-loops. Formation of Lnc530-DDX5-TDP-43 complex substantially increases the local protein levels of DDX5 and TDP-43, both of which play critical roles in R-loop regulation. This study uncovers an efficient strategy to prevent R-loop accumulation and preserve genomic stability in mESCs and possibly other stem cell types.

Replication stress is a major source of endogenous DNA damage. Despite the identification of numerous proteins on replication forks to modulate fork or replication machinery activities, it remains unexplored whether noncoding RNAs can localize on stalled forks and play critical regulatory roles. Here, we identify an uncharacterized long noncoding RNA NONMMUT028956 (Lnc956 for short) predominantly expressed in mouse embryonic stem cells. Lnc956 is accumulated on replication forks to prevent fork collapse and preserve genomic stability and is essential for mouse embryogenesis. Mechanistically, it drives assembly of the Lnc956-TRIM28-HSP90B1 complex on stalled forks in an interdependent manner downstream of ataxia telangiectasia and Rad3-related (ATR) signaling. Lnc956-TRIM28-HSP90B1 complex physically associates with minichromosome maintenance proteins 2 (MCM2) to minichromosome maintenance proteins 7 (MCM7) hexamer via TRIM28 and directly regulates the CDC45-MCM-GINS (CMG) helicase retention on chromatin. The regulation of Lnc956-TRIM28-HSP90B1 on CMG retention is mediated by HSP90B1's chaperoning function. These findings reveal a player that actively regulates replisome retention to prevent fork collapse.

Maintaining genomic stability is crucial for embryonic stem cells (ESCs). ESCs with unrepaired DNA damage are eliminated through differentiation and apoptosis. To date, only tumor suppressor p53 is known to be implicated in this quality control process. Here, we identified a p53-independent quality control factor lncRNA NONMMUT028956 (Lnc956 for short) in mouse ESCs. Lnc956 is prevalently expressed in ESCs and regulates the differentiation of ESCs after DNA damage. Mechanistically, Ataxia telangiectasia mutated (ATM) activation drives m6A methylation of Lnc956, which promotes its interaction with Krüppel-like factor 4 (KLF4). Lnc956-KLF4 association sequestrates the KLF4 protein and prevents KLF4’s transcriptional regulation on pluripotency. This posttranslational mechanism favors the rapid shutdown of the regulatory circuitry of pluripotency. Thus, ATM signaling in ESCs can activate two pathways mediated by p53 and Lnc956, respectively, which act together to ensure robust differentiation and apoptosis in response to unrepaired DNA damage.

This study comprehensively analyzed the fates of antibiotics, antibiotic resistance genes (ARGs) and microbial community during upgrading process of municipal wastewater treatment plant (MWTP) of Anaerobic/Anoxic/Oxic-membrane bioreactor (A(2)/O-MBR) from regulation to stable operation phase. The factors most affecting ARGs profile were investigated, and the potential hosts for ARGs were further determined. Results showed that the removal rate of total antibiotics and the reduction of ARGs increased by 10.49% and 1.37 logs in A(2)/O-MBR during upgrading process, respectively. The most prevalent ARG was sul1 in both water and sludge phase. Mobile genetic elements (MGEs) and microbial community were the most significant factors affecting ARGs distribution in water phase and sludge, respectively. Notably, the abundance of potential antibiotic resistance bacteria (ARB) was significantly decreased during upgrading process. Therefore, sul1and intI1 proliferation as well as microbial community succession should be emphasized in ARGs pollution management and control. This study expected to provide a theoretical basis for the application of MBR process to remove antibiotics and ARGs in upgrading of MWTPs.

RPA is a master regulator of DNA metabolism and RPA availability acts as a rate-limiting factor. While numerous studies focused on the post-translational regulations of RPA for its functions, little is known regarding how RPA availability is controlled. Here we identify a novel lncRNA Discn as the guardian of RPA availability in stem cells. Discn is induced upon genotoxic stress and binds to neucleolin (NCL) in the nucleolus. This prevents NCL from translocation into nucleoplasm and avoids undesirable NCL-mediated RPA sequestration. Thus, Discn-NCL-RPA pathway preserves a sufficient RPA pool for DNA replication stress response and repair. Discn loss causes massive genome instability in mouse embryonic stem cells and neural stem/progenigor cells. Mice depleted of Discn display newborn death and brain dysfunctions due to DNA damage accumulation and associated inflammatory reactions. Our findings uncover a key regulator of DNA metabolism and provide new clue to understand the chemoresistance in cancer treatment.

Endogenous DNA double-strand breaks (DSBs) formation and repair in neural stem/progenitor cells (NSPCs) play fundamental roles in neurogenesis and neurodevelopmental disorders. NSPCs exhibit heterogeneity in terms of lineage fates and neurogenesis activity. Whether NSPCs also have heterogeneous regulations on DSB formation and repair to accommodate region-specific neurogenesis has not been explored. Here, we identified a regional regulator Filia, which is predominantly expressed in mouse hippocampal NSPCs after birth and regulates DNA DSB formation and repair. On one hand, Filia protects stalling replication forks and prevents the replication stress-associated DNA DSB formation. On the other hand, Filia facilitates the homologous recombination-mediated DNA DSB repair. Consequently, Filia(-/-) mice had impaired hippocampal NSPC proliferation and neurogenesis and were deficient in learning, memory, and mood regulations. Thus, our study provided the first proof of concept demonstrating the region-specific regulations of DSB formation and repair in subtypes of NSPCs.

The author group of the article is not displayed in the web/online version, though the information appeared in print version.