The Chrysanthemum genus (Asteraceae) is a key polyploidy model, but its complex genomes obscure its origin and evolution. To address this, we developed chromosome-set-specific painting probes from the Chrysanthemum morifolium 'Zhongshanzigui' haploid genome, enabling precise identification of all nine chromosome sets. Combined with existing oligonucleotide probes (Oligo-Mix: CmOP-1 and CmOP-2), we established a novel sequential fluorescence in situ hybridization (FISH) procedure for comparative genomic analysis. Applying this across six Chrysanthemum species revealed extraordinarily conserved chromosomal synteny. Analysis of diploids (e.g. C. nankingense, C. lavandulifolium, and C. indicum) and their derived autotetraploids showed autopolyploidization involved amplification of large-scale repetitive sequences and loss of partial repeats. Crucially, rapid cytological diploidization (diploid-like bivalent pairing) occurred, associated with significant enrichment of repetitive sequences at meiotic crossover (CO) loci on homologous chromosomes. This leads us to hypothesize that repetitive DNA variation may facilitate precise chromosome segregation and diploid-like meiosis, thereby potentially ensuring polyploid stability. These findings provide essential tools for distinguishing homologous chromosomes and significant potential for elucidating homologous interactions to advance polyploid Chrysanthemum breeding.

Meiotic progression requires the activity of the cyclin B-CDK1 complex. In this issue, Yang et al. (https://doi.org/10.1083/jcb.202502087) demonstrate that the phospho-adaptor protein CKS-1 functions as a critical component of this complex to ensure proper chromosome segregation during oocyte meiosis.

Causes and consequences of chromosomal cohesin loss: Novel insights for mechanisms of aging-related oocyte aneuploidy.

Chromosome organization by Structural Maintenance of Chromosomes complexes in C. elegans.

Osteoporosis (OP) is a degenerative skeletal disorder marked by a decrease in bone mineral density, which significantly raises the risk of fractures. The development of OP is closely associated with oxidative stress (OS), yet the specific molecular targets of OS in the context of OP, as well as the corresponding therapeutic strategies, are not well understood. This study aimed to systematically identify OS-related biomarkers for OP and explore potential therapeutic agents, providing new insights into the pathological mechanisms and precision therapy of OP. OP-related datasets (GSE56815 as the training set and GSE35958 as the validation set) were obtained from the gene expression omnibus database. Integrated with OS-related genes from GeneCards, 72 co-expressed differentially expressed genes associated with both OP and OS were identified. A protein–protein interaction network was constructed using search tool for the retrieval of interacting genes/proteins, and 9 hub genes were identified via Maximal Clique Centrality and MCODDE algorithms. Three core genes (SIRT2, neutrophil elastase [ELANE], and forkhead box O3 [FOXO3]) were further selected using random forest and support vector machine models. Diagnostic accuracy of key genes was evaluated by receiver operating characteristic curves. Immune infiltration analysis was performed with ImmuCellAI, while transcription factors were predicted through NetworkAnalyst to establish a miRNA-seed-transcription factor (TF) regulatory network. Potential drugs were screened from DGIdb, and molecular docking was conducted with CB-DOCK2 using ligand–protein structures from PubChem and UniProt. A FOXO3/sirtuin 1 (SIRT1) functional axis was subsequently constructed. The 72 differentially expressed genes showed enrichment in cell division, chromosome segregation, and cell cycle pathways. SIRT2, ELANE, and FOXO3 exhibited high diagnostic accuracy for OP (area under the curve > 0.7). Immune infiltration analysis revealed significant differences in key immune cells and subtypes between OP and controls. The miRNA–seed–TF network implicated miR-34a and miR-132. Molecular docking confirmed stable binding of 5 compounds to targets. Critically, the FOXO3–SIRT1 axis was identified as mediating oxidative stress in OP pathogenesis. FOXO3 and SIRT2 were upregulated; ELANE downregulated. This study identified SIRT2, ELANE, and FOXO3 as key OS-related biomarkers for OP and screened 5 potential therapeutic compounds. Integrating miRNA–TF network and drug sensitivity analysis, we propose the FOXO3/SIRT1 axis as central to OP oxidative stress, providing a foundation for mechanistic studies and targeted drug development.

Integrated omics and machine learning uncover the molecular basis of environmental toxicant 6PPD-Qinduced non-obstructive azoospermia.

DNA-protein cross-links (DPCs) are highly toxic DNA lesions that block replication and transcription, but their impact on organismal physiology is unclear. We identified a role for the metalloprotease SPRTN in preventing DPC-driven immunity and its pathological consequences. Loss of SPRTN activity during replication and mitosis lead to unresolved DNA damage, chromosome segregation errors, micronuclei formation, and cytosolic DNA release that activates the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway. In a Sprtn knock-in mouse model of Ruijs-Aalfs progeria syndrome, chronic cGas-Sting signaling caused embryonic lethality through inflammation and innate immune responses. Surviving mice displayed aging phenotypes beginning in embryogenesis, which persisted into adulthood. Genetic or pharmacological inhibition of cGas-Sting rescued embryonic lethality and alleviated progeroid phenotypes.

Meiotic chromosome segregation requires reciprocal exchanges between the parental chromosomes (homologs). Exchanges form via tightly-regulated repair of double-strand DNA breaks (DSBs). However, since repair intermediates have been mostly quantified in fixed images, our understanding of the mechanisms that control repair progression remains limited. Here, we study meiotic repair kinetics in Caenorhabditis elegans by extinguishing new DSBs and following the disappearance of a crucial intermediate - strand invasion mediated by the conserved RecA-family recombinase RAD-51. Assuming exponential decay, RAD-51 foci have a half-life of 1-2 hours, with >75% of foci disappearing within 4 hours. Previous work suggested that sister-directed repair is specifically blocked throughout most of pachytene. In contrast, we find that RAD-51 foci half-lives are 1-2 hours even in conditions where homolog engagement is prevented and only the sister is available as a template. This suggests that both sister- and homolog-engaged RAD-51 foci are continuously turned over during pachytene. We also use our kinetic information to revisit the total number of DSBs - the 'substrate' for the formation of exchanges - and find an average of 20-38 DSBs per nucleus. Our work opens the door for analysis of the interplay between meiotic repair kinetics and the fidelity of genome inheritance.

For proper segregation of chromosomes and successful cytokinesis, chromosomes must first "congress"-gather in a tight plate near the spindle equator. Molecular mechanism(s) of congression are not fully understood. Here we combine live-cell microscopy, perturbations of microtubule motor activities, correlative light/electron microscopy, and computational modeling, to quantitatively characterize the early-prometaphase movements that bring the scattered chromosomes to the equator in human RPE1 cells. We find that the early-prometaphase movements are directed toward the center of the spindle axis and not the spindle poles. Centromere velocity of the centripetal movements is not constant, with centromeres moving faster at larger distances from the spindle center. We also detect that numerous short microtubules appear at kinetochores at the earliest stages of spindle assembly and prior to chromosome congression. Computational modeling reveals that a mechanism based on brief, stochastic, minus-end directed interactions between the short microtubules protruding from the kinetochores and long appropriately curved microtubules within the spindle accurately predicts the observed distance-velocity function. Further, the model predicts that insufficient numbers of microtubules protruding from the kinetochores decreases the velocity and randomizes directionality of congression movements. These predictions match changes in the chromosome behavior observed in cells with suppressed nucleation of microtubules at the kinetochore corona (RPE1 RodΔ/Δ). In contrast, predictions of computational models based on continuous pulling forces at kinetochores differ significantly from the experimental observations. Together, live-cell observations and modeling reveal a mechanism that enables the efficient and synchronized arrival of chromosomes to the spindle equator.

Meiotic recombination ensures accurate chromosome segregation and genetic diversity during gametogenesis, and its disruption leads to infertility. The dual histone methylation writer–reader system, in which PRDM9 deposits H3K4me3 and H3K36me3 marks at nucleosomes to define recombination hotspots and ZCWPW1 acts as a reader recognizing these marks, is essential for meiotic recombination. However, the regulatory mechanisms of this system remain unclear. Here, we showed that deficiency of ZCWPW2 causes recombination defects in humans and mice, including impaired homologous chromosome synapsis and defective DNA double-strand break repair. CUT&Tag analysis revealed that ZCWPW2 exhibits increased enrichment at dual H3K4me3 and H3K36me3 sites in the presence of PRDM9, while binding to promoter regions independently of PRDM9 to regulate meiotic transcription. Mass spectrometry further showed that ZCWPW2 forms a complex with ZCWPW1 and interacts with recombination-associated proteins in a ZCWPW1-dependent manner. Mechanistically, we demonstrate that the ZCWPW1–ZCWPW2 complex enhances the functions of key lactylation regulators LDHA and EP300, thereby promoting lactylation of recombination-associated proteins and stabilizing their abundance. Collectively, we identify ZCWPW2 as a previously unrecognized but essential factor in meiotic recombination, elucidate the molecular mechanism of the PRDM9/ZCWPW1/ZCWPW2 system in regulating recombination, and uncover a critical role for lactylation in meiosis.

The leading cause of human pregnancy loss is aneuploidy, often tracing to errors in chromosome segregation during female meiosis1,2. Although abnormal crossover recombination is known to confer risk for aneuploidy3,4, limited data have hindered understanding of the potential shared genetic basis of these key molecular phenotypes. To address this gap, we performed retrospective analysis of pre-implantation genetic testing data from 139,416 in vitro fertilized embryos from 22,850 sets of biological parents. By tracing transmission of haplotypes, we identified 3,809,412 crossovers, as well as 92,485 aneuploid chromosomes. Counts of crossovers were lower in aneuploid versus euploid embryos, consistent with their role in chromosome pairing and segregation. Our analyses further revealed that a common haplotype spanning the meiotic cohesin SMC1B is associated significantly with both crossover count and maternal meiotic aneuploidy, with evidence supporting a non-coding cis-regulatory mechanism. Transcriptome- and phenome-wide association tests also implicated variation in the synaptonemal complex component C14orf39 and crossover-regulating ubiquitin ligases CCNB1IP1 and RNF212 in meiotic aneuploidy risk. More broadly, variants associated with aneuploidy often showed secondary associations with recombination, and several also exhibited associations with reproductive ageing traits. Our findings highlight the dual role of recombination in generating genetic diversity, while ensuring meiotic fidelity.

Crystal structure of the cell-cycle regulatory monopolar spindle one binder (LdMOB1) protein: Identification of potential distinct phosphorylation sites.

SUMMARYCell fate transitions rely on extensive transcriptional activation mediated by transcription factors, yet the equally important processes that ensure the selective removal of pre-existing mRNAs remain elusive. We uncover widespread formation of double-stranded RNA (dsRNA) during early-to-middle meiosis using quantitative RNA structure analysis, and validate hundreds of natural antisense transcripts (NATs) through long-read sequencing. These NATs are induced by meiosis-specific transcription factors, including Ndt80p, and pair with sense mRNAs to drive cytoplasmic aggregation of the resulting dsRNAs. These dsRNA aggregates are subsequently transported to the vacuole for clearance, likely via autophagy. This pathway selectively eliminates mRNAs before metaphase I, includingNDJ1, which encodes a meiotic cohesion protein that would otherwise block chromosome segregation. Our study reveals a physiological role for large-scale dsRNA formation, and highlights a simple but powerful model: the same transcription factors that activate mRNAs required for a specific developmental stage also program the synthesis of NATs that promote removal of transcripts from the preceding stage, thereby driving bidirectional transcriptome reprogramming.

Chromosome segregation in the human pathogen Streptococcus pneumoniae relies on the membrane-binding protein RocS, which links the chromosomal DNA to the membrane. Beside the ability of RocS to bind DNA and interact with the chromosome partitioning protein ParB, little is known about how C-terminal membrane anchor of RocS contributes to chromosome segregation. More precisely, the molecular basis of membrane targeting remains unresolved. This study addresses the interplay between RocS C-terminal region and the lipid membrane. Combined magic-angle spinning NMR and wide-line NMR reveal that the membrane anchoring peptide folds into a short membrane-inserted kink-helix motif connected to an extended linker, with membrane insertion locally perturbing lipid packing. The fluidity of the lipid bilayer, modulated by temperature, in turn influences the anchor-membrane interactions. At the mesoscale, AFM imaging shows that the anchor selectively associates with lipid nanodomains, clustering into discrete foci. Mutational studies further reveals that a single glycine mutation in the C-terminal significantly perturbs chromosome segregation and alters lipid membrane properties. These findings reveal a mechanism for nanodomain association of a highly conserved membrane-targeting motif in Streptococci, highlighting the kink-helix anchor as a conserved element for membrane targeting across bacteria and beyond.

Resolution of sister chromatid intertwines in mitosis is vital for safeguarding genome integrity. While cohesin, condensin, the polo-like kinase Cdc5, and the phosphatase Cdc14 have all been implicated in this process, the underlying molecular mechanisms remain elusive. Our study unveils a coordination between spindle elongation and the timely resolution of DNA linkages, orchestrated by Cdc14 and Cdc5. We show that Cdc14 and Cdc5 collaborate to facilitate the resolution of DNA catenanes, the predominant species of DNA intertwines in mitosis, by regulating Topoisomerase II (Top2) function, both through SUMOylation and phosphorylation. Our findings contribute to unraveling a mechanism wherein Cdc5 and Cdc14 work together to ensure the timely removal of all sources of linkages between sister chromatids, thereby preserving the integrity of chromosome segregation and genome stability.

We report that Aurora B kinase-mediated phosphorylation is essential for BubR1 acetylation at lysine 250 (K250), a modification required to preserve the mitotic checkpoint complex (MCC) and ensure accurate chromosome segregation. This Aurora B–BubR1 acetylation axis provides a mechanistic explanation for how kinetochore–microtubule attachment status is transduced to spindle assembly checkpoint (SAC) activity. Aurora B phosphorylates BubR1 at Serine 39 (and Ser16) in response to unattachment, and this phosphorylation is indispensable for subsequent K250 acetylation. Using a monoclonal anti-AcK250 antibody in structured illumination microscopy, we demonstrate that BubR1 acetylation sustains the fibrous corona, as shown by the crescent-shaped expansion of ZW10 and MAD2 surrounding kinetochores. Loss of either CENP-E or BubR1 acetylation abolishes fibrous corona, indicating that the interaction between acetylated BubR1 and CENP-E connects lateral attachment with the prevention of premature corona disassembly until proper end-on attachment is achieved. Disruption of Aurora B-mediated phosphorylation compromises K250 acetylation, fibrous corona maintenance, and MCC stability, whereas expression of a K250 acetylation-mimetic BubR1 rescues these defects in S16A/S39A phosphorylation-deficient mutants. Together, our findings establish a phosphorylation–acetylation cascade in BubR1 as a critical SAC signaling pathway and identify this axis as a promising therapeutic target in cancers driven by chromosomal instability.

Homologs of the polar landmark proteins HubP and FimV are widespread among bacterial species. They all share several common features, including a periplasmic LysM-like domain, a transmembrane region, an extensive cytoplasmic domain enriched in acidic amino acids, and a C-terminal tetrapeptid-repeat (TPR) domain referred to as the FimV domain. Apart from these conserved general features, however, the proteins exhibit little homology across different bacterial genera. Here, we characterized Pseudomonas putida FimV (PpFimV) with respect to cellular processes involving FimV or HubP in other species. We found that PpFimV nonspecifically binds to peptidoglycan via its periplasmic LysM domain, which, together with an immunoglobulin-like domain, is necessary for proper polar positioning. PpFimV is required for normal flagellar-mediated swimming and the placement of the chemotaxis system. However, PpFimV is not involved in regulating the number of flagellar filaments, chromosome segregation, or type IV pilus-dependent surface motility. Thus, PpFimV has surprisingly little functional overlap with, for example, HubP from Vibrio sp. or Shewanella putrefaciens or with FimV from P. aeruginosa. PpFimV was unable to compensate for the loss of SpHubP with regard to swimming in soft agar, and vice versa. Domain swapping between SpHubP and PpFimV revealed that differences in the cytoplasmic region between the transmembrane region and the C-terminal FimV domain likely account for the proteins' distinct functions in flagella-mediated swimming. This suggests that FimV and HubP are structural homologs that have evolved to perform different, species-specific functions.IMPORTANCEMany bacterial species possess landmark proteins that organize the bacterial cell and localize specific cellular processes to the cell's polar regions by directing client proteins or protein complexes to their designated positions. FimV and its homolog HubP are landmark proteins found in many species of the gammaproteobacteria, but their roles are not well understood. Here, we demonstrate that only certain functions related to flagella-mediated motility appear to be conserved between Pseudomonas putida FimV and Shewanella putrefaciens HubP. This finding suggests a significant degree of functional diversity.

Protein degradation orders events in the cell division cycle in eukaryotes, bacteria, and archaea. In eukaryotes, chromosome segregation and mitotic exit are triggered by proteasome-dependent degradation of securin and cyclin B, respectively. Recent findings show that the archaeal proteasome also targets substrates, including CdvB, for degradation in a cell-cycle-dependent manner in Sulfolobus acidocaldarius-an experimentally tractable archaeal relative of eukaryotes. Here, using CdvB as a model substrate to explore the mechanism of cyclic protein degradation, we demonstrate that the C-terminal broken-winged helix of CdvB, previously shown to bind CdvA, is sufficient to render a fusion protein unstable as cells progress through division. We show that the rate of CdvB degradation accelerates during division in part due to a cell-cycle-dependent increase in expression of the proteasome-activating nucleotidase (PAN), under the control of a cyclically expressed novel transcription factor "CCTF1" that represses PAN expression. Taken together, these findings reveal mechanisms by which archaea, despite lacking cyclin-dependent kinases, control proteasome-mediated degradation to order events during cell division.

BackgroundThere is substantial heterogeneity in clinical presentation of genetic Frontotemporal Dementia (FTD), even within the same family. This suggests that additional heritability may exist and contribute to this variable presentation. We examined whether gene‐based aggregate burden of genome‐wide rare variants (minor allele frequency [MAF]: ≤1%) contribute to variation in regional cortical and subcortical grey matter volumes, after controlling for effects of causative mutations in GRN, MAPT, and C9orf72.MethodThis study was embedded within the GENetic Frontotemporal dementia Initiative (GENFI), which recruits genetic FTD cases and their asymptomatic at‐risk family members, both carriers and non‐carriers of FTD mutations. We included 518 participants with genotype (Neurochip; imputed against TOPMed), and T1w‐MRI brain volumetric data. Gene‐based burden tests that aggregate the number of rare variants by gene were used to examine the association of rare variants (MAF: ≤1%) with regional cortical and subcortical grey matter volumes (70 regions of interest [ROIs]), controlling for age, sex, total intracranial volume, mutation status, scanner site, population stratification, and family membership (kinship matrix) using RVTests. Annotations for loss of function mutations (LOF): start gain, stop loss, start loss, essential splice site, stop gain, normal splice site, and non‐synonymous. Multiple testing correction accounted for the number of genes and number of independent grey matter volumes as calculated by matSpD (p‐value threshold: 0.05/(17,053x42) = 6.98 x10‐8).ResultAggregate burden of LOF mutations (DNAJB8‐AS1, WDR26, RDM1P5, BSND, CNOT2, DDA1, ASAH2B, PPM1A, HOXD13, ALDH1A1, CENATAC, ANKRD45) was associated with significantly lower volumes within the left temporal lobe (ROIs: left temporal and lateral temporal left), and greater volume in the putamen bilaterally (TSACC). All genes are protein coding, except the DNAJB8‐AS1 (antisense RNA) and RDM1P5 (pseudogene), and are variably expressed in the brain. Molecular functions of significant genes involve regulation of gene expression, transcription, and cell cycle, ion channel function, and chromosomal segregation. WDR26 and CNOT2 genes have been implicated in neurodevelopment and neurological disorders respectively; BSND gene is involved in neurotransmission.ConclusionIdentification of deleterious or protective rare variants contributing to FTD imaging phenotypes may help identify genetic modifiers of familial FTD. Replication in larger cohorts is needed.

Centriole elimination is an evolutionarily conserved, essential process during gametogenesis that resets centrosome number to prevent aneuploidy in the zygote (Schatten & Sun, 2011). While in vitro gametogenesis (IVG) from pluripotent stem cells offers transformative potential for reproductive medicine, its fidelity in recapitulating key cytoplasmic organelle reprogramming events remains poorly characterized. This study presents a systematic comparative analysis of centriole elimination dynamics between natural mouse gametogenesis and leading IVG protocols. Employing high-resolution imaging, molecular profiling, and functional embryogenesis assays, we demonstrate that IVG-derived gametes exhibit profound defects. Centriole elimination in vitro is asynchronous, frequently incomplete, and driven by a dysregulated molecular cascade, leading to the persistent retention of structurally aberrant centrioles (Clift & Schuh, 2013). These organelles act as ectopic microtubule-organizing centers, causing multipolar spindle formation during meiosis and the first embryonic division. Consequently, embryos from IVG gametes with centriole retention suffer catastrophic failure, characterized by severe chromosome segregation errors and preimplantation arrest (Hendriks, Dancet, van Pelt, Hamer, & Repping, 2015). Our findings establish centriole elimination fidelity as a critical, previously overlooked benchmark for IVG. They reveal that the artificial microenvironment fails to provide the precise niche signaling required for this stringent developmental program, highlighting a major safety consideration and providing a mechanistic roadmap for refining synthetic gametogenesis protocols.