EMBO Journal最新文献

A hallmark of Alzheimer's disease (AD) is the accumulation of extracellular amyloid-β plaques in the brain. Amyloid-β is a 40-42 amino acid peptide generated by proteolytic processing of amyloid precursor protein (APP) via membrane-bound proteases. APP is a transmembrane protein, and its trafficking to sites of proteolysis represents a rate-limiting step in AD progression. Although APP processing has been well-studied, its trafficking itinerary and machinery remain incompletely understood. To address this, we performed an unbiased interaction screen for interactors of the APP cytosolic tail. We identified previously characterised APP binders as well as novel interactors, including RABGAP1. We demonstrated that RABGAP1 partially co-localises with APP and directly interacts with a YENPTY motif in the APP cytosolic tail. Depletion or overexpression of RABGAP1 caused mistrafficking and misprocessing of endogenous APP in human and rodent neurons. This effect is dependent on the GAP activity of RABGAP1, demonstrating that RABGAP1 affects the trafficking of APP by modulating RAB activity on endosomal subdomains. This novel trafficking mechanism has implications for other NPXY cargoes and presents a possible therapeutic avenue to explore.

DNA is a substrate for competing protein-mediated activities. Whether and how transcription and the synaptic steps of recombination collide or are coordinated has not been investigated. Here, using a controlled break induction system and physical detection of D-loop DNA joint molecules in S. cerevisiae, we show that donor transcription by RNA polymerase II strongly and acutely suppresses D-loops in cis. The extent of this suppression depends on the orientation of transcription, suggesting the preferential usage of one end for the repair of DNA break in transcribed regions. Transcription-mediated D-loop suppression does not rely on endogenous transcription factors, the RNA product, or RNA:DNA hybrids. It is independent of, and can be more potent than the conserved trans D-loop-disruption factors Sgs1-Top3-Rmi1^{BLM-TOPO3α-RMI1/2}, Mph1^FANCM, and Srs2. This transcription-mediated control promotes genome maintenance by inhibiting ectopic recombination and multi-invasion-induced rearrangements, while authorizing allelic inter-homolog repair. These findings reveal the prioritization between two universal DNA-dependent processes and its role in promoting genome stability.

Tumor heterogeneity, a hallmark of cancer, frequently leads to treatment failure and relapse. However, the intricate communication between various cell types within the tumor microenvironment and their roles in tumor progression in vivo remain poorly understood. Here we establish a novel tumor heterogeneity model in the Drosophila larval eye disc epithelium and dissect the in vivo mechanisms by combining sophisticated genetics with single-cell RNA sequencing. We found that mutation of the tricellular junction protein M6 in cells surrounding RasV12 benign tumors promotes their malignant transformation. Mechanistically, early RasV12//M6-/- tumors secrete Pvf1, which activates the Pvr receptor on hemocytes, facilitating their recruitment to the tumor site. These tumor-associated hemocytes secrete the Spätzle (Spz) ligand to activate the Toll receptor within the RasV12 tumors. This enhanced activation of the Toll pathway synergizes with RasV12 to promote malignant transformation through the JNK-Hippo signaling cascade. In summary, our study elucidates the complex interplay between genetically distinct oncogenic cells and between tumors and hemocytes, highlighting how hemocytes exploit the ancient innate immune system to coordinate tumor heterogeneity and drive tumor progression.

Insulin resistance is a heritable risk factor for many chronic diseases; however, the genetic drivers remain elusive. In seeking these, we performed genetic mapping of insulin sensitivity in 670 chow-fed Diversity Outbred in Australia (DOz) mice and identified a genome-wide significant locus (QTL) on chromosome 8 encompassing 17 defensin genes. By taking a systems genetics approach, we identified alpha-defensin 26 (Defa26) as the causal gene in this region. To validate these findings, we synthesized Defa26 and performed diet supplementation experiments in two mouse strains with distinct endogenous Defa26 expression levels. In the strain with relatively lower endogenous expression (C57BL/6J) supplementation improved insulin sensitivity and reduced gut permeability, while in the strain with higher endogenous expression (A/J) it caused hypoinsulinemia, glucose intolerance and muscle wasting. Based on gut microbiome and plasma bile acid profiling this appeared to be the result of disrupted microbial bile acid metabolism. These data illustrate the danger of single strain over-reliance and provide the first evidence of a link between host-genetics and insulin sensitivity which is mediated by the microbiome.

Type-III interferons (or IFNλs) play important roles in antiviral defense and intestinal epithelial barrier integrity. While interferon expression has been primarily studied in response to pathogens, basal interferon expression also occurs in pathogen-free environments. However, the mechanisms regulating basal IFN-λ expression and their functions have not yet been elucidated. Here, we show that basal IFN-λ2/3 expression is linked to the development of an intact cellular epithelium characterized by formation of tight junctions and establishment of barrier function. Our findings indicate that basal IFN-λ2/3 expression depends on cGAS-STING-mediated mitochondrial DNA detection, while it is inhibited by the Hippo mechanotransduction pathway at low cellular densities. Cells lacking basal IFN-λ2/3 expression fail to develop proper tight junctions and establish normal barrier function. Mechanistically, IFN-λ2/3 suppresses Claudin-2 expression, thereby promoting barrier formation as cells become confluent. These results demonstrate a previously unknown function of basal IFNλ expression in regulating epithelial cell junction formation and highlight their importance not only during pathogen challenges but also in maintaining epithelial cell function under steady-state conditions.

Gut microbial species contribute to colorectal cancer (CRC) by interacting with tumor or immune cells, however if CRC-associated bacteria engage with stromal components of the tumor microenvironment remains unclear. Here, we report interaction between the CRC-associated bacterium Fusobacterium nucleatum and cancer-associated fibroblasts (CAFs), and show that F. nucleatum is present in the stromal compartment in murine CRC models in vivo and can attach to and invade CAFs. F. nucleatum-exposed CAFs exhibit a pronounced inflammatory-CAF (iCAF) phenotype, marked by elevated expression of established iCAF markers, secretion of pro-inflammatory cytokines such as CXCL1, IL-6 and IL-8, generation of reactive oxygen species (ROS), and an increased metabolic activity. In co-culture experiments, the interaction of cancer cells with F. nucleatum-stimulated CAFs enhances invasion, a finding further validated in vivo. Altogether, our results point to a role for the tumor microbiome in CRC progression by remodeling the tumor microenvironment through its influence on cancer-associated fibroblasts, suggesting novel therapeutic strategies for targeting CRC.

The Rcs signal transduction system is a phosphorelay responsible for sensing enterobacterial cell envelope stresses. In Escherichia coli, the Rcs system is required to survive treatment with A22 and mecillinam, antibiotics that perturb cell size. To test whether size changes are correlated with envelope damage and thereby sensed by the Rcs system, we tuned E. coli cell size via A22 treatment, mutations in the cell-shape determinant MreB, and mechanically confined growth. In all conditions, cell width was strongly correlated with Rcs activation, and RcsF, the outer-membrane-localized upstream component, was essential for responding to cell width changes. Several gene deletions that induce Rcs resulted in cells that were wider than wild-type. Cryo-electron microscopy revealed that the periplasm of a wide MreB mutant is ~3 nm thinner than in wild-type cells, bringing RcsF closer to the downstream, inner-membrane-localized components of the signaling cascade. Conversely, extending the RcsF linker region in wild-type cells by ~3 nm increased Rcs activity. Thus, we propose that the Rcs system responds to changes in cell width due to altered periplasmic thickness.

In mouse early pachytene spermatocytes, the X and Y chromosomes undergo rapid non-homologous (NH) synapsis and desynapsis, but the functional significance remains unknown. Here, we report that pachynema-specific knockout of Speedy A (SpdyA) from telomeres caused persistent Y-X NH synapsis, with the entire Y axis synapsed onto the X axis. This persistent Y-X NH synapsis did not interrupt meiotic sex chromosome inactivation, recombination, or sex body formation, but it disrupted X-Y loop-axis organization and homologous X-Y desynapsis, leading to spermatocyte death. Similarly, persistent Y-X NH synapsis was also observed in pachytene spermatocytes lacking TRF1, where SpdyA was frequently lost from the X-Y non-pseudoautosomal region (non-PAR) telomeres. Mechanistic studies revealed that Serine 48 of SUN1 is a key SpdyA/CDK2 phosphorylation site required for Y-X NH desynapsis. We propose that SpdyA governs Y-X NH desynapsis by stabilizing the linkage between the X-Y non-PAR telomeres and their LINC complexes, and that this process is regulated independently from other aspects of pachynema progression. Our findings suggest a key role for Y-X NH desynapsis in establishing proper X-Y loop-axis organization.