EMBO Journal最新文献

The meiotic segregation pattern to generate haploid gametes is mediated by step-wise cohesion removal by separase, first from chromosome arms in meiosis I, and then from the pericentromere in meiosis II. In mammalian oocytes, separase is tightly controlled during the hours-long prometaphase and until chromosome segregation in meiosis I, activated for a short time window, and again inhibited until metaphase II arrest is lifted by fertilization. Centromeric cohesin is protected from cleavage by Sgo2-PP2A in meiosis I. It remained enigmatic how tight control of alternating separase activation and inactivation is achieved during the two divisions in oocytes, and when cohesin protection is put in place and removed. Using complementation assays in knock-out mouse models, we established the contributions of cyclin B1 and securin for separase inhibition during both divisions. When eliminating separase inhibition, we found that cohesin is not robustly protected at meiosis I resumption and during metaphase II arrest. Importantly, in meiosis II, the sole event required for cleavage of pericentromeric cohesin besides separase activation is prior kinetochore individualization in meiosis I.

Synovial sarcoma (SySa) is an aggressive soft tissue sarcoma with an urgent need to develop targeted therapies. Here, we exploited specific vulnerabilities created by transcriptional rewiring by the fusion protein SS18::SSX, the sole oncogenic driver in SySa. To uncover genes that are selectively essential for the fitness of SySa cells compared to other tumor cell lines, we mined  the Cancer-Dependency-Map data. Targeted CRISPR library screening of SySa-selective candidates revealed that the small ubiquitin-like modifier 2 (SUMO2) constituted one of the strongest dependencies both in vitro and in vivo. TAK-981, a clinical-stage small-molecule SUMO2 inhibitor potently suppressed growth and colony-forming ability. Transcriptomic profiling showed that SUMO2 inhibition elicited a profound reversal of the gene expression program orchestrated by SS18::SSX fusion. Further, genetic depletion or SUMO2 inhibition reduced global expression levels and chromatin occupancy of the SS18::SSX fusion protein with a concomitant reduction in histone 2A lysine 119 ubiquitination (H2AK119ub), an epigenetic mark facilitating SySa pathogenesis. Taken together, our study identifies SUMO2 as a novel, selective vulnerability in synovial sarcoma, suggesting new avenues for targeted treatment of soft tissue tumors.

Telomere shortening occurs in multiple tissues throughout aging. When telomeres become critically short, they trigger DNA-damage responses and p53 stabilization, leading to apoptosis or replicative senescence. In vitro, cells with short telomeres activate the cGAS-STING innate immune pathway resulting in type-I interferon-based inflammation and senescence. However, the consequences of these events for the organism are not yet understood. Here, we show that sting is responsible for premature aging of telomerase-deficient zebrafish. We generated sting-/- tert-/- double-mutant animals and observed a thorough rescue of tert-/- phenotypes. At the cellular level, lack of cGAS-STING in tert mutants resulted in reduced senescence, increased cell proliferation, and decreased inflammation despite similarly short telomeres. Critically, absence of sting function resulted in dampening of the DNA damage response and reduced p53 levels. At the organism level, sting-/- tert-/- zebrafish regained fertility, showed delayed cachexia, and decreased cancer incidence, resulting in increased healthspan and lifespan of telomerase mutant animals.

DNA N⁶-methyladenine (6mA) is an emerging epigenetic mark in the mammalian genome. ALKBH1 preferentially exhibits 6mA demethylase activity for single-stranded DNA (ssDNA) or bubbled/bulged DNA, but not for double-stranded DNA (dsDNA). Nevertheless, ALKBH1 significantly decreases the cellular 6mA level in genomic DNA, whose prevailing DNA conformation in living mammalian cells is dsDNA. Therefore, the demethylase activity of ALKBH1 toward 6mA in genomic DNA, especially dsDNA, remains largely debated. Here, we found that YTHDF3 increases the 6mA demethylase activity of ALKBH1 in genomic DNA with different conformations, including dsDNA. Compared with ALKBH1, YTHDF3 preferentially recognizes and binds to 6mA-modified DNA with different conformations. YTHDF3 recognizes 6mA in genomic DNA, and binds ALKBH1 to recruit it to sites near 6mA in genomic DNA, thereby facilitating the ALKBH1-mediated removal of 6mA in genomic dsDNA. In summary, YTHDF3 is a novel genomic DNA reader and guides ALKBH1 to remove 6mA in human genomic DNA.

Neuronal communication relies on precisely maintained synaptic vesicle (SV) clusters, which assemble via liquid-liquid phase separation. This process requires synapsins, the major synaptic phosphoproteins, which are known to bind actin. Reorganization of SVs, synapsins, and actin is a hallmark of synaptic activity, but the molecular details of the interactions between these components remain unclear. Here, we combine in vitro reconstitution with expansion microscopy, super-resolution imaging, and cryo-electron tomography to dissect the roles of SV-synapsin-1 condensates in the organization of the presynaptic actin cytoskeleton. Our results indicate that condensation of synapsin-1 initiates actin polymerization. This process enables SV-synapsin-actin assemblies to facilitate the mesoscale organization of SV clusters along axons, which is similar to the native presynaptic organization observed at both lamprey and mammalian synapses. Understanding the relationship between the actin network and synapsin-synaptic vesicle condensates can help elucidate how coordinated neurotransmission along the axon enables circuit function and behavior.

Recent developments in single-cell -omic and metabolite imaging technologies and the increasing availability of high-quality genome assemblies are having a transformative impact on the way research is carried out into plant specialised metabolism. Integrating these technologies into pathway discovery projects is therefore highly advantageous. Here, we present a general introduction into methods and workflows in specialised metabolism research. We review a range of recent methodologies, highlighting what they might be used for and common pitfalls which may be encountered. Finally, we provide a practical guide on how these technologies may be incorporated into a specialised metabolic pathway discovery pipeline for researchers who are new to the field.

Exhaustion of CD8⁺ T-cells leads to their reduced immune functionality and is controlled by numerous transcription factors. Here we show that the transcription factor IRF-5 helps to limit functional exhaustion of murine CD8⁺ T-cells during the chronic stage of LCMV (CL13) viral infection. Our results suggest that T-cell inhibitory receptors and transcription factor TOX, which are implicated in dampening T-cell activation and promoting exhaustion, are upregulated in infected IRF-5-deficient CD8⁺ T-cells. In addition, these cells display a reduced capacity to produce cytokines and lower survival rates than wild-type cells. Our findings indicate that these effects are mediated by defective lipid metabolism, increased lipid peroxidation, enhanced mitochondrial ROS production, and reduced levels of oxidative phosphorylation in the absence of IRF-5. These results identify IRF-5 as an important regulator of lipid metabolism and mitochondrial function that protects CD8⁺ T-cells from functional exhaustion during the chronic stage of viral infection.

Oocytes, female germ cells that develop into eggs, are among the longest-lived cells in the animal body. Recent studies on mouse oocytes highlight unique adaptations in protein homeostasis (proteostasis) within these cells. However, the mechanisms of proteostasis in human oocytes remain virtually unstudied. We present the first large-scale study of proteostatic activity in human oocytes using over 100 freshly donated oocytes from 21 healthy women aged 19-34 years. We analysed the activity and distribution of lysosomes, proteasomes, and mitochondria in both immature and mature oocytes. Notably, human oocytes exhibit nearly twofold lower proteolytic activity than surrounding somatic cells, with further decreases as oocytes mature. Oocyte maturation is also coupled with lysosomal exocytosis and a decrease in mitochondrial membrane potential. We propose that reduced organelle activity preserves key cellular components critical for early embryonic development during the prolonged maturation of human oocytes. Our findings highlight the distinctive biology of human oocytes and the need to investigate human-specific reproductive biology to address challenges in female fertility.

Eukaryotic genomes replicate in a defined temporal order called the replication timing (RT) program. RT is developmentally regulated with the potential to drive cell fate transitions, but mechanisms controlling RT remain elusive. We previously identified "Early Replication Control Elements" (ERCEs), cis-acting elements necessary for early RT, domain-wide transcription, 3D chromatin architecture and compartmentalization in mouse embryonic stem cells (mESCs), but deletions identifying ERCEs were large and encompassed many putative regulatory elements. Here, we show that ERCEs are compound elements, whose RT activity can largely be accounted for by multiple binding sites for diverse master transcription factors (subERCEs). While deletion of subERCEs had large effects on both transcription and replication timing, deleting transcription start sites eliminated nearly all transcription with only moderate effects on replication timing. Our results suggest a model in which subERCEs are a class of transcriptional enhancers that can also organize chromatin domains structurally to support early replication timing, potentially providing a feed-forward loop to drive robust epigenomic change during cell fate transitions.