Although poly(ADP-ribose) polymerase inhibitors (PARPi) show promise for treating homologous recombination-deficient cancers, the observed PARPi hypersensitivity in additional genetic contexts expands their potential use in precision oncology. Yet, the DNA lesions driving PARPi-induced cytotoxicity remain poorly defined. Here we uncover distinct replication-fork lesions in specific genomic regions as key determinants of PARPi cytotoxicity. Using CRISPR screens, we identify that loss of replication-coupled cohesin acetyltransferase ESCO2 confers PARPi hypersensitivity independently of homologous recombination deficiency. Quantitative single-molecule imaging reveals that ESCO2 loss promotes accumulation of G-quadruplex (G4) DNA structures at a subset of replication-associated sites, associated with PARP1 activation and engagement of fork protection factor TIMELESS to mitigate G4-induced stress. Notably, these G4 lesions localize to fragile pericentromeric regions and engage the G4 helicase DDX11. PARP inhibition disrupts this protective G4-processing response by preventing PARP1-dependent engagement of TIMELESS and DDX11, leading to G4 accumulation, DNA damage and chromosomal instability. Together, our findings define the G4–PARP1–TIMELESS–DDX11 axis as a critical safeguard of replication fork stability at hard-to-replicate loci and reveal ESCO2 as a therapeutic target for promoting synthetic lethality in PARPi-treated cancers. Through CRISPR screens and single-molecule imaging, Gupta et al. show that loss of the cohesion acetyltransferase ESCO2 leads to increased G-quadruplex formation at specific regions and drives PARP activation and PARPi hypersensitivity.
Tauopathies, such as Alzheimer’s disease, are neurodegenerative disorders characterized by the accumulation and propagation of toxic extracellular forms of the microtubule-associated protein tau across brain regions. Microglia, the resident macrophages of the brain, are known for clearing and degrading toxic proteins. However, emerging evidence suggests that microglia also enhance tau spreading. To dissect the molecular mechanisms underlying microglial responses to extracellular tau, we use high-resolution imaging and biochemical approaches to assess the trafficking dynamics of different extracellular tau species in human induced pluripotent stem cell-derived microglia. Here we find that tau monomers are internalized by microglia via cell-surface LRP1 receptors but fail to reach terminally degradative lysosomes; instead, they are persistently recycled back to the extracellular space. In contrast, tau fibrils are not internalized and primarily adhere to the cell surface through an HSPG-dependent mechanism, triggering TLR4-mediated microglial activation and the release of pro-inflammatory cytokines. Heparin or anti-tau treatments dampen tau fibril-mediated microglial activation. In addition, disease-associated variants of the Alzheimer’s disease-related protein APOE reduce microglia–tau interactions, further reducing tau uptake. Together, these findings demonstrate that microglia fail to efficiently clear extracellular tau monomers and fibrils through mechanistically distinct cellular processes, emphasizing the need for tailored therapeutic strategies to enhance extracellular tau clearance in neurodegenerative diseases. Kulkarni et al. show distinct fates of monomeric versus fibrillar tau in human induced pluripotent stem cell-derived microglia. Monomeric tau is internalized but does not reach degradative lysosomes; fibrillar tau adheres to the cell surface and triggers microglial activation.
Differential Hippo–LATS–YAP signalling controls the first mammalian cell-fate decision, yet how human trophectoderm specification progresses to chorion formation remains unknown. Here we establish a developmentally informed model in which LATS kinase inhibition initiates the trophectoderm trajectory without exogenous morphogens. Stage matching to an integrated embryo–chorion single-cell reference revealed ordered progression from early trophectoderm to secondary chorionic lineages. Whole-genome bisulfite sequencing showed a naive-like hypomethylated state followed by remethylation, with key known placenta-associated imprinted domains retaining methylation and allelic bias. We then established a three-dimensional human chorion model by agitating induced-cell aggregates in suspension, yielding secondary chorionic lineages that self-organized with outward-facing trophoblast polarity and inside-out stromal–epithelial topology. Endogenous WNT signalling was dispensable for initial trophectoderm induction but regulated later chorionic lineage balance. Isolating CLDN6+ITGA6− cells identified a proEVT-like intermediate with villous and extravillous potential. Together, this framework connects human trophectoderm induction to three-dimensional chorion modelling and enables investigation of placental specification. Zhang et al. establish a developmentally informed human stem cell model that specifies trophectoderm via Hippo pathway modulation and can self-organize into a three-dimensional model capturing aspects of human chorion development.
