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L1 insertion intermediates recombine with one another or with DNA breaks to form genome rearrangements.

LINE-1 retrotransposition is common in human cancers and rearrangements at insertion sites can contribute to cancer-driving oncogene amplifications and promote genome instability. However, the mechanisms underlying rearrangements of L1 retrotransposition intermediates are poorly understood. To address this gap, we developed GFP-based recombination reporter assays to study the formation of L1 retrotransposition-mediated rearrangements. Using these reporters combined with long-read sequencing approaches, we find that L1 retrotransposition intermediates can recombine with distal DNA breaks to generate chromosomal rearrangements. We also find that two distinct L1 insertion intermediates can recombine with each other to generate chromosomal rearrangements. Both types of rearrangements depend on L1-encoded ORF2p endonuclease and reverse transcriptase activities. Using these reporters, we discover that L1 retrotransposition-mediated rearrangements are robustly induced when the recombining sequences share homology and that their formation requires the homologous recombination factor BRCA1. Given the repetitive nature of our genome, these findings highlight the risk of L1 insertion intermediates becoming substrates for aberrant recombination and promoting genome instability.

L1 retrotransposons

The immediate-early protein 1 of human herpesvirus 6B interacts with NBS1 and inhibits ATM signaling.

Viral infection often trigger an ATM serine/threonine kinase (ATM)-dependent DNA damage response in host cells that suppresses viral replication. Viruses evolved different strategies to counteract this antiviral surveillance system. Here, we report that human herpesvirus 6B (HHV-6B) infection causes genomic instability by suppressing ATM signaling in host cells. Expression of immediate-early protein 1 (IE1) phenocopies this phenotype and blocks homology-directed double-strand break repair. Mechanistically, IE1 interacts with NBS1, and inhibits ATM signaling through two distinct domains. HHV-6B seems to efficiently inhibit ATM signaling as further depletion of either NBS1 or ATM do not significantly boost viral replication in infected cells. Interestingly, viral integration of HHV-6B into the host's telomeres is not strictly dependent on NBS1, challenging current models where integration occurs through homology-directed repair. Given that spontaneous IE1 expression has been detected in cells of subjects with inherited chromosomally-integrated form of HHV-6B (iciHHV-6B), a condition associated with several health conditions, our results raise the possibility of a link between genomic instability and the development of iciHHV-6-associated diseases.

Humans

A high-quality draft genome assembly of Johnsongrass illuminates relationships between polyploidization, crop-wild hybridization, and reproductive biology.

Johnsongrass [Sorghum halepense (L.) Pers.] is an allopolyploid, rhizomatous, perennial grass species and one of the most troublesome weeds in global agriculture. We assembled the first Johnsongrass genome to clarify poorly understood genetic factors influencing variable rates of crop-wild hybridization with cultivated sorghum [S. bicolor (L.) Moench]. The draft genome assembly has a total size of 3.26 Gb and BUSCO completeness of 95.3%. We also report the first evolutionary analysis of INHIBITION OF ALIEN POLLEN (IAP), the only known cross-(in)compatibility locus in the genus. Our results reveal an evolutionary history of genome instability, including the loss of distinct parental subgenomes, and suggest that Nebraska accession 'J-37,' the genome donor, is a segmental allotetraploid that may function as a diploid or aneuploid during meiosis. Genome instability could explain observations of variable ploidies in Johnsongrass and facilitate ongoing hybridization with sorghum where gamete ploidies and IAP alleles match. Given this information, we provide a suggested research framework for studying evolution and gene expression in the Sorghum genus where crop-wild hybridization occurs and for predicting the potential for hybridization between specific crossing partners. Collectively, this work will bolster efforts to study and manage reproductive biology in other crop-wild polyploid complexes.

Sorghum

Loss of Fbxo45 in AT2 cells leads to insufficient histone supply and initiates lung adenocarcinoma.

Dysregulation of histone supply is implicated in various cancers, including lung adenocarcinoma (LUAD), although the underlying mechanisms remain poorly understood. Here, we demonstrate that knockout of Fbxo45 in mouse alveolar epithelial type 2 (AT2) cells leads to spontaneous LUAD. Our findings reveal that FBXO45 is a novel cell-cycle-regulated protein that is degraded upon phosphorylation by CDK1 during the S/G2 phase. During the S phase or DNA damage repair, FBXO45 binds to UPF1 and recruits the phosphatase PPP6C, thereby inhibiting UPF1 phosphorylation. This process is crucial for preventing the degradation of replication-dependent (RD) histone mRNAs and ensuring an adequate histone supply. In the absence of FBXO45, the impaired interaction between PPP6C and UPF1 results in sustained hyperphosphorylation of UPF1 throughout the cell cycle, leading to an insufficient histone supply, chromatin relaxation, genomic instability, and an increased rate of gene mutations, ultimately culminating in malignant transformation. Notably, analysis of clinical LUAD specimens confirms a positive correlation between the loss of FBXO45 and genomic instability, which is consistent with our findings in the mouse model. These results highlight the critical role of FBXO45 as a genomic guardian in coordinating histone supply and DNA replication, providing valuable insights into potential therapeutic targets and strategies for the treatment of LUAD.

Animals

A stratified urine-based molecular diagnostic and prognostic model for non-muscle-invasive bladder cancer management.

BACKGROUND: Non-muscle-invasive bladder cancer (NMIBC) is characterized by a high recurrence rate requiring lifelong cystoscopic surveillance. Existing urine-based molecular assays mainly rely on mutations or methylation, which fail to capture large-scale genomic instability. Copy number variation (CNV) profiling offers complementary information on tumor evolution and aggressiveness, but its application in urinary diagnosis remains limited. We aimed to integrate CNV and DNA methylation signals from urinary DNA to establish a noninvasive and biologically informed stratified diagnostic model for NMIBC recurrence surveillance and risk stratification. METHODS: Urine samples were prospectively collected from 91 patients (75 evaluable) between June 2021 and August 2023. Shallow whole-genome sequencing (sWGS) was used to detect CNVs at chromosomal arm and focal gene levels, while ONECUT2 promoter methylation was quantified by qPCR. Diagnostic and prognostic performance was evaluated by ROC analysis, Kaplan-Meier survival, and stratified recurrence assessment. RESULTS: We evaluated a stratified diagnostic model combining CNV and ONECUT2 methylation testing in a cohort of 79 patients. CNV analysis alone showed high specificity (0.923) for NMIBC diagnosis. A combined model, using CNV as an initial screen followed by ONECUT2 methylation testing in CNV-positive cases, achieved a sensitivity of 0.783, specificity of 0.981, and a negative predictive value (NPV) of 0.911. This approach reduced the number of required ONECUT2 tests by 35% and identified a high proportion of true-negative patients (98.1%), which may help reduce unnecessary cystoscopy procedures. The model also demonstrated significant prognostic value, with the molecularly defined high-risk group showing significantly shorter recurrence-free survival (RFS) than the low-risk group (median RFS: 4.33 months vs. not reached; p&#x2009;<&#x2009;0.001). Additional, in patients with initially negative cystoscopy after urine sample collection, the model demonstrated a predictive accuracy of 0.922 for recurrence, with molecular positivity observed a median of 9.6 months prior to clinical diagnosis. CONCLUSIONS: Integrating CNV and DNA methylation profiling from urinary DNA provides a powerful and noninvasive molecular framework for NMIBC surveillance. By combining early epigenetic changes with genomic instability signals, this approach enhances recurrence risk assessment and enables earlier detection compared with conventional cystoscopy. It offers a practical route toward personalized and adaptive post-treatment monitoring of NMIBC. TRIAL REGISTRATION: NCT04994197.

Humans

Integrated transcriptomic and immunogenomic analysis unravels the immunological functions and prognostic landscape of WD repeat domain 76.

BackgroundWD Repeat Domain 76 (WDR76) plays a potential role in cellular regulation; however, its comprehensive landscape across human malignancies and its specific biological function in hepatocellular carcinoma (HCC) remain largely unexplored.MethodsWe conducted a systematic pan-cancer analysis utilizing multi-omics data from The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Cancer Cell Line Encyclopedia (CCLE) atabases to evaluate WDR76 expression, subcellular localization, and its correlation with clinicopathologic features, genomic instability, and immune infiltration. Diagnostic and prognostic values were assessed via Receiver operating characteristic (ROC) and Kaplan-Meier analyses. Furthermore, the functional role of WDR76 in HCC was validated in vitro using Hep-3B and Huh7 cell lines through siRNA-mediated knockdown, followed by CCK-8, wound-healing, and transwell assays.ResultsWDR76 was significantly upregulated in the majority of tumor types, including LIHC, LUAD, and COAD, while exhibiting nuclear localization. Elevated WDR76 expression correlated with advanced tumor staging, metastasis, and poor clinical outcomes across multiple cohorts, particularly in ACC, KIRP, and LIHC. ROC analysis highlighted its exceptional diagnostic precision in cancers such as GBM and LIHC. Immunologically, WDR76 expression was intricately linked to immune cell infiltration, immune checkpoint markers, and genomic instability parameters, suggesting a role in shaping the tumor microenvironment. Drug sensitivity profiling revealed that high WDR76 levels correlate with resistance to specific chemotherapeutic agents. Experimentally, silencing WDR76 in HCC cells significantly suppressed cell proliferation, migration, and invasion capabilities.ConclusionOur study establishes WDR76 as a robust pan-cancer prognostic biomarker and a potential immunotherapeutic target. Specifically, we provide experimental evidence that WDR76 functions as an oncogenic driver in liver cancer, promoting malignant phenotypes and offering a novel avenue for targeted therapeutic intervention.

Humans

RADX protects against intestinal inflammation by restraining IFI16-mediated innate immunity.

Genomic instability is increased in patients with inflammatory bowel disease (IBD), yet whether it contributes directly to disease pathogenesis remains unclear. Here, we identify RADX, a structural antagonist to RAD51 and a key regulator of replication fork stability, as a critical suppressor of intestinal inflammation by limiting innate immune sensing of replication-associated DNA damage. RADX deficiency exacerbates experimental colitis, with macrophages serving as the principal mediators of this phenotype. Mechanistically, RADX competes with the DNA sensor IFI16 for binding to single-stranded DNA (ssDNA). Loss of RADX promotes ssDNA accumulation, triggering IFI16-dependent activation of NF-&#x3ba;B signaling and inflammasome assembly, thereby driving intestinal inflammation. Consistent with these findings, two RADX variants identified in patients with IBD associate with reduced RADX protein expression, increased DNA damage signaling, and elevated IL-1&#x3b2; levels. Pharmacological inhibition of RAD51 with RI-1 alleviated colitis in both wild-type and Radx-deficient mice. Together, these findings establish a mechanistic link between genome instability and intestinal inflammation, identify a RADX-IFI16 checkpoint that restrains pathogenic innate immune activation, and nominate modulation of replication stress as a therapeutic strategy for IBD.

Animals

Efficiency of DNA repair mechanisms of domestic dog primary fibroblasts isolated from small and large breeds of different ages in response to double stranded breaks (DSB).

Aging is associated with increased genomic instability, a phenomenon largely driven by the accumulation of DNA damage over time, and large species of mammals seem to have more robust DNA repair systems associated with longer lives. Among DNA lesions, double-strand breaks (DSBs) are particularly deleterious and have been implicated in age-related functional decline and disease. In this study, we investigated how age and body mass affect the efficiency of DSB repair (DSBr) in primary fibroblast cells isolated from domestic dogs, a species that exhibits significant intraspecies variation in lifespan and body mass. Primary fibroblast cells were isolated from puppies and senior dogs of both large and small breeds. Cells were treated with 100&#xa0;&#xb5;M etoposide to induce DSBs and subsequently analyzed at two post-treatment recovery intervals (2 and 24&#xa0;h) to correlated with the two pathways associated with DSBr, the fast, non-homologous end joining (NHEJ) and the much slower, homologous recombination (HR). Cells were stained for &#x3b3;-H2AX foci and images were collected using confocal microscopy. We found that mean fluorescence per cell was higher in older dogs of both size classes in the 2&#xa0;h recovery, indicating higher amounts of DNA damage but suggesting similar efficiencies through the NHEJ repair mechanism in older dogs despite size class. We also show that mean fluorescence per cell was higher in the older large breed dogs in the 24&#xa0;h recovery, suggesting that the slower phase associated with HR seems to be deficient in cells from older, larger breeds of dogs. These findings support the broader theory that aging is associated with impaired genomic maintenance and establish domestic dogs as a valuable model for studying the cellular mechanisms of age-related genomic instability.

Animals

Stratifying lung adenocarcinoma: a novel prognostic model based on mitochondrial outer membrane permeabilization activity.

UNLABELLED: Mitochondrial outer membrane permeabilization (MOMP) is a core apoptotic regulatory event that dictates mitochondrial integrity, where full activation drives cell death and sublethal dysregulation contributes to tumor genomic instability. We used the Cancer Genome Atlas lung adenocarcinoma cohort (TCGA-LUAD) as the training cohort and the Gene Expression Omnibus dataset GSE42127 as the validation cohort to identify prognostic genes related to MOMP activity in lung adenocarcinoma (LUAD) and to evaluate their potential biological significance. By intersecting MOMP-related genes with differentially expressed genes, combined with survival analysis, Mendelian randomization analysis, and 101 machine-learning algorithm combinations, seven prognostic genes, namely BIRC5, PSMD11, TNFRSF13C, YWHAZ, YWHAG, CYCS, and LTB, were identified. Next, an optimal prognostic model was constructed based on the gradient boosting machine (GBM) algorithm. Based on the risk score, LUAD patients were stratified into high- and low-risk groups, and patients in the high-risk group exhibited poorer overall survival in both the training and validation cohorts. Furthermore, a nomogram integrating the risk score and clinicopathological factors was developed and showed favorable predictive performance for 1-, 3-, and 5-year survival. Meanwhile, functional and immune analyses revealed that the high-risk group was enriched in DNA replication-related pathways and demonstrated a higher tumor mutation burden (TMB). Correlation analysis indicated that TNFRSF13C was positively correlated with activated B cells, whereas BIRC5 was negatively correlated with eosinophils, suggesting that MOMP-related genes might be involved in remodeling the immune microenvironment of LUAD. Drug sensitivity analysis showed differences in predicted half-maximal inhibitory concentration (IC50) values between the risk groups, suggesting the potential value of this model in assisting therapeutic stratification. Single-cell RNA sequencing (scRNA-seq) further identified T lymphocytes as a key cell type, with numerous prognostic genes exhibiting differential expression in T cells or dynamic changes during differentiation. We suggest that the MOMP-related signature established in this study may provide a reference for prognostic stratification in LUAD and offers candidate prognostic genes for subsequent experimental and clinical validation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1007/s13205-026-05058-6.

Lung adenocarcinoma

In vitro fertilization-conceived offspring exhibit altered Long Interspersed Nuclear Elements-1 retrotransposition dynamics associated with long-term disease risks.

BACKGROUND: In vitro fertilization has transformed reproductive medicine, yet offspring conceived through in vitro fertilization display elevated risks for diverse long-term health conditions, with underlying mechanisms unclear. Long Interspersed Nuclear Elements-1, a mobile genetic element responsive to environmental stress, represents a potential mediator. OBJECTIVE: This study aimed to test the hypothesis that in vitro fertilization procedures may act as an embryonic stressor that alters Long Interspersed Nuclear Elements-1 dynamics, potentially contributing to genomic instability associated with long-term disease susceptibility. STUDY DESIGN: Umbilical cord blood or peripheral blood from 33 in vitro fertilization and 42 naturally conceived neonates were collected for whole-genome sequencing. Total Long Interspersed Nuclear Elements-1 proportion in individual genome was counted with Bowtie2 software. De novo Long Interspersed Nuclear Elements-1 insertion and Long Interspersed Nuclear Elements-1 deletion were detected with Mobile Element Locator Tool. Three parent-matched in vitro fertilization-naturally conceived sibling pairs were included to control for genetic background. Disease association analysis was performed for genes within 500 kb of differential Long Interspersed Nuclear Elements-1 sites in The Database for Annotation, Visualization and Integrated Discovery (DAVID). Statistical analysis was performed using the R language. RESULTS: In vitro fertilization offspring demonstrate elevated global Long Interspersed Nuclear Elements-1 content compared to naturally conceived controls (P=.04). This finding was corroborated in 3 sibling pairs from identical genetic backgrounds, where in vitro fertilization-conceived children consistently exhibited higher Long Interspersed Nuclear Elements-1 levels than their naturally conceived siblings. Eleven genomic loci with differential Long Interspersed Nuclear Elements-1 insertion frequencies and 14 loci with differential Long Interspersed Nuclear Elements-1 deletion frequencies between in vitro fertilization offspring and naturally conceived controls were identified. Notably, these differential Long Interspersed Nuclear Elements-1 sites demonstrated significant enrichment near genes implicated in metabolic, cardiovascular, neuropsychiatric, and neoplastic diseases, conditions associated with in vitro fertilization conception. CONCLUSION: These findings provide preliminary evidence that in vitro fertilization conception is associated with increased Long Interspersed Nuclear Elements-1 content and altered genomic distribution of Long Interspersed Nuclear Elements-1 elements. The proximity of these differential Long Interspersed Nuclear Elements-1 sites to disease-associated genes suggests a plausible genomic mechanism linking in vitro fertilization-associated embryonic stress to elevated disease risk. This work provides valuable molecular insights that may inform the ongoing discussion about assisted reproductive technology safety and suggests that continued attention to genomic integrity in in vitro fertilization-conceived individuals would be beneficial.

Humans

Somatic mutations and genome mosaicism in aging and disease.

Age-related genome mosaicism is an inherent feature of multicellularity and genomic instability. It occurs because of DNA mutations, the accumulation of which leads to diverse genomic landscapes across different tissues. DNA mutations in the genome are consequences of DNA damage, changes in the chemical structure of DNA, such as strand breaks or loss of bases. DNA damage is very frequent and normally repaired quickly. However, errors intrinsic to DNA repair or replication can give rise to permanent changes in genome sequence information. Such DNA mutations are diverse and include single-nucleotide variants, small insertions and deletions, and larger genome structural variants. Since the 1950s, somatic mutations have been proposed to be a major cause of aging. Indeed, somatic mutations are the cause of cancer, the risk of which increases exponentially with age, and possibly other age-related diseases, such as neurodegenerative diseases and cardiomyopathies. Somatic mutations vary from cell to cell owing to the innate stochasticity of their occurrence, from error-prone processing of randomly inflicted DNA damage. With the emergence of single-cell and single-molecule sequencing, it has become possible to quantitatively analyze somatic mutations in human cells and tissues. Here, we discuss a possible causal relationship between mutation-driven mosaicism of the somatic genome and aging-related functional decline and disease by exploring several predictions of the somatic mutation theory of aging.

Humans

Acute Myeloid Leukemia With KMT2A Amplification: A TP53-Alteration-Enriched Subgroup Associated With Chromoanagenesis and Poor Prognosis.

KMT2A amplification (KMT2A-amp) is a rare but aggressive genomic abnormality in acute myeloid leukemia (AML), with limited characterization in prior studies. We retrospectively analyzed 96 patients with AML harboring KMT2A-amp, including 56 newly diagnosed (ND) and 40 relapsed/refractory (RR) cases, with a median age of 68 years. Approximately half of the cases had therapy-related or secondary AML. All cases demonstrated highly complex karyotypes, with frequent -5/del(5q), -7/del(7q), and -17/del(17p). TP53 alteration was present in 93% of patients, whereas other recurrent AML-associated mutations were uncommon, and no AML-defining gene fusions or mutations were identified. In cases evaluated by optical genome mapping, all showed chromoanagenesis involving chromosome 11q23 region. Clinical outcomes were poor, with a median overall survival of 5.5 months in ND and 2.3 months in RR patients. Intensive chemotherapy did not improve survival compared with lower-intensity therapy, whereas venetoclax-based regimens were associated with improved overall survival (7.1 vs 4.6 months; p = 0.04) and event-free survival (6.7 vs 0.17 months; p < 0.01). We conclude that KMT2A-amp AML represents an extremely high-risk subgroup occurring in the context of TP53-associated genomic instability and chromoanagenesis. Its refractoriness to conventional chemotherapy highlights the urgent need for more effective, targeted therapeutic strategies.

KMT2A amplification

Frequent mutations in the BIRC3 gene promote metastatic potential of nasopharyngeal carcinoma cells through the TRAF2-NF-&#x3ba;B pathway.

Nasopharyngeal carcinoma (NPC) is a head and neck cancer characterized by highly locoregionally invasive behavior attributable to the latent infection with Epstein-Barr virus (EBV) and genomic instability. It is well established that EBV-encoded oncogenic molecules actively contribute to the malignant behavior of NPC cells. However, the mechanism by which aberrant genomic alterations enable NPC cells to become aggressive remains largely unknown. In the present study, whole-exome sequencing (WES) revealed that the gene encoding the baculoviral IAP repeat-containing 3 (BIRC3) protein was frequently mutated in circulating tumor cells (CTCs) but not in paired primary tumor cells from patients with metastatic NPC. A minigene assay indicated that the c.637&#xa0;A&#xa0;>&#xa0;G mutation disrupted normal mRNA splicing, resulting in the partial deletion of Exons 2 and 3 and altered stability of BIRC3 mRNA. In vitro experiments demonstrated that ectopic expression of the BIRC3c.637A>G mutant enhanced NPC cell invasive properties, including proliferation, resistance to apoptosis, migration, and invasion. Furthermore, overexpression of wild-type BIRC3 promoted invasive characteristics in NPC cells through the TRAF2-NF-&#x3ba;B signaling axis. In summary, BIRC3 acts as a regulator of the malignant features of NPC cells. Frequent BIRC3 mutations in CTCs, such as the c.637&#xa0;A&#xa0;>&#xa0;G mutation, further enhance the metastatic potential of disseminated NPC cells by inducing aberrant alternative splicing. These findings suggest the therapeutic feasibility of targeting the BIRC3/TRAF2/NF-&#x3ba;B axis in the treatment of NPC.

Humans

Targeting innovative therapeutic approaches to the hallmarks of aging to combat Alzheimer's disease.

Aging is the leading risk factor for neurodegenerative diseases, including Alzheimer's disease. Mounting evidence implicates twelve interconnected hallmarks of aging, such as genomic instability, mitochondrial dysfunction, cellular senescence, and altered intercellular communication, as core contributors to cognitive decline. In this review, we will first delineate the hallmarks of aging and their mechanistic roles according to their functions in the aging brain and Alzheimer's disease. These hallmarks can be grouped into four major functional clusters: (i) Genomic and epigenomic instability, (ii) proteostasis and organelle dysfunction, (iii) cellular fate and regenerative decline, and (iv) cellular senescence. Then, we provide an overview of innovative therapeutic approaches aimed at modifying these hallmarks, focusing on the emerging paradigm of supplementation of rejuvenation factors that are derived from young plasma, stem cell secretomes, or their derivatives (e.g., extracellular vesicles). Finally, we discuss key aging-related biological factors that can influence Alzheimer's disease progression and evaluate their potential as therapeutic targets.

Alzheimer&#x2019;s disease

KLHL13 functional defects cause neurodevelopmental disorder in humans that can be rescued via inhibition of AURKB in cellular and animal models.

PURPOSE: Neurodevelopmental disorders (NDDs) are characterized by limitations in brain development. This study aims to determine the genetic causes of NDD in humans. METHODS: Exome sequencing was used to detect genetic variants of KLHL13, which encodes Kelch like protein 13 (KLHL13), in four families segregating in an X-linked pattern. In silico protein modeling and overexpression in heterologous cells were used to determine the variant's impact. klhl13 loss of function was modeled in zebrafish, followed by rescue studies using human KLHL13 messenger RNA (mRNA) and an Aurora Kinase B (AURKB) inhibitor. RESULTS: We found one frameshift and three missense hemizygous variants of KLHL13 in individuals exhibiting NDD characteristics, such as intellectual disability (ID) and macrocephaly. Three-dimensional protein modeling simulation predicted the alteration of the KLHL13 protein folding for missense variants. Overexpression of NDD-associated variants in HEK293T cells revealed a significant impact on KLHL13-mediated cell-cycle regulation during mitosis, leading to genomic instability. Knocking down klhl13 in zebrafish resulted in developmental deficits, which were rescued by coinjection of human KLHL13WT messenger RNA but not by transcript encoding NDD variants. Treatment with AURKB selective inhibitor AZD1152-HQPA rescued genomic stability in heterologous cells and neurobehavioral deficits in zebrafish. CONCLUSION: Our results implicate KLHL13-mediated AURKB regulation as a significant contributor to NDD in humans. Inhibiting AURKB activity could serve as a potential therapeutic approach to improve brain development and cognitive function.

Humans

Evolutionary fingerprints of epithelial-to-mesenchymal transition.

Mesenchymal plasticity has been extensively described in advanced epithelial cancers; however, its functional role in malignant progression is controversial1-5. The function of epithelial-to-mesenchymal transition (EMT) and cell plasticity in tumour heterogeneity and clonal evolution is poorly understood. Here we clarify the contribution of EMT to malignant progression in pancreatic cancer. We used somatic mosaic genome engineering technologies to trace and ablate malignant mesenchymal lineages along the EMT continuum. The experimental evidence clarifies the essential contribution of mesenchymal lineages to pancreatic cancer evolution. Spatial genomic analysis, single-cell transcriptomic and epigenomic profiling of EMT clarifies its contribution to the emergence of genomic instability, including events of chromothripsis. Genetic ablation of mesenchymal lineages robustly abolished these mutational processes and evolutionary patterns, as confirmed by cross-species analysis of pancreatic and other human solid tumours. Mechanistically, we identified that malignant cells with mesenchymal features display increased chromatin accessibility, particularly in the pericentromeric and centromeric regions, in turn resulting in delayed mitosis and catastrophic cell division. Thus, EMT favours the emergence of genomic-unstable, highly fit tumour cells, which strongly supports the concept of cell-state-restricted patterns of evolution, whereby cancer cell speciation is propagated to progeny within restricted functional compartments. Restraining the evolutionary routes through ablation of clones capable of mesenchymal plasticity, and extinction of the derived lineages, halts the malignant potential of one of the most aggressive forms of human cancer.

Animals

RAD54L coordinates the nucleolar DNA damage response to maintain rDNA stability.

The nucleolus is organized around actively transcribed ribosomal RNA genes (rDNA), where high RNA polymerase I (Pol I) activity creates intrinsic susceptibility to replication stress and DNA damage. Here, we identify the DNA translocase RAD54L as a critical regulator of the nucleolar DNA damage response (nDDR) to rDNA double-strand breaks (DSBs) and replication stress. We show that RAD54L localizes to the nucleolus under basal conditions and is recruited to nucleolar caps following CRISPR-Cas9-induced rDNA-DSBs to promote repair. RAD54L loss results in persistent RAD51 foci, increased&#xa0;nucleolar &#x3b3;H2AX, and micronuclei formation, indicating defective resolution of rDNA lesions and genome instability. Under baseline conditions and replication stress induced by the Pol I transcription inhibitor CX-5461, RAD54L limits the accumulation of ssDNA and coordinates nDDR signaling. We further show that rDNA-DSBs induce RNA polymerase II-dependent&#xa0;RNA-DNA hybrids (R-loops)&#xa0;at intergenic rDNA&#xa0;regions, which facilitate nucleolar reorganization and cap formation and&#xa0;repair&#xa0;factor recruitment. Together, these findings establish RAD54L as a key regulator that coordinates replication stress response and rDNA repair, maintaining rDNA stability and genome integrity.

DNA, Ribosomal

Telomere Crisis Shapes Cancer Evolution.

Somatic mutations arise in normal tissues and precursor lesions, often targeting cancer-driver genes involved in cell cycle regulation. Most checkpoint-mutant clones, however, remain dormant throughout an individual's lifetime and seldom progress to malignancy, implying the presence of protective mechanisms that limit their expansion and malignant transformation. One such safeguard is telomere crisis-a potent tumor-suppressive barrier that eliminates cells lacking functional checkpoints and evading p53- and pRb-mediated surveillance. While the genomic instability unleashed during telomere crisis can drive clonal evolution, cell death is typically the dominant outcome, with only a rare subset of cells escaping elimination to initiate malignancy. Recognizing the dual role of telomere crisis-suppressing tumor initiation while enabling clonal evolution-is essential for understanding early cancer development and designing strategies to eliminate tumor-initiating cells.

Neoplasms