Journal of Cell Biology

Cargo receptors are central organizers of the secretory pathway, yet the mechanisms controlling their abundance remain poorly understood. The endoplasmic reticulum (ER)-resident intramembrane protease RHBDL4 promotes substrate turnover via a non-canonical branch of ER-associated degradation and has recently been implicated in regulating secretory pathway components. We previously identified the p24 cargo receptor TMED7 as an RHBDL4 substrate, suggesting that cargo receptor turnover contributes to secretory pathway regulation. Here, quantitative proteomics identify members of the ER-Golgi intermediate compartment (ERGIC) cargo receptor family as endogenous RHBDL4 substrates, demonstrating that RHBDL4 targets multiple cargo receptor families within the early secretory pathway. Accordingly, RHBDL4 modulates multiple ERGIC-dependent transport pathways. In addition, unbiased secretome analysis reveals increased secretion of lysosomal precursor proteins upon RHBDL4 ablation. Mechanistically, we show that this phenotype is mediated, at least in part, by RHBDL4-dependent cleavage of the lysosomal cargo receptor sortilin/SORT1. Together, these findings identify cargo receptors as a major class of RHBDL4 substrates and establish proteolytic remodeling of cargo receptor networks as a mechanism for regulating secretory pathway flux.

Peripheral sensory neurons innervate the skin to detect mechanical, thermal, and noxious stimuli. Within the epidermis, nerve fibers terminate beneath tight junctions, shielding them from environmental exposure. Although epidermal differentiation coordinates tight junction assembly, its role in organizing nerve terminals is poorly understood. Here, we show that activation of Notch, a master regulator of epidermal differentiation, caused near-complete loss of epidermal innervation. This was largely the result of increased contractility rather than impaired differentiation. Inducing epidermal contractility was sufficient to deplete nerve fibers with striking spatial precision, and restoring normal contractility reversed this effect. Actomyosin contractility is highest in the granular layers of the epidermis, where tight junctions form and nerve fibers terminate. Ablation of nonmuscle myosin II allowed nerve fibers to extend beyond their normal termination zone and caused touch hypersensitivity. Together, these findings demonstrate that epidermal contractility positions sensory nerve endings through spatially controlled pruning and defines a mechanical boundary established by epidermal cells that restricts neuronal outgrowth.

Skin, the bodys largest mechanosensitive organ, relies on a tension gradient across epidermal layers to maintain structure and function, but how mechanical force contributes to epidermal development and disease pathogenesis is poorly understood. By anchoring intermediate filaments (IF) to the plasma membrane, desmosomes, the most abundant intercellular junctions in the epidermis, help create a supracellular scaffolding that provides mechanical resilience to the tissue. However, the contribution of the desmosome-IF network to the epidermal response to mechanical strain remains unknown. Here we show that the desmosome-IF connection is not only required to induce a proper cellular mechano-response but is actively strengthened in response to stretch through the PP2A-mediated phospho-regulation of the cytoskeletal linker protein desmoplakin (DP). Additionally, we show in human skin dephosphorylated DP localizes to high tension layers, suggesting this mechano-response mechanism is coordinated with the epidermal tension gradient. Furthermore, in models of Carvajal syndrome, a cardio-cutaneous disorder caused by truncating DP mutations, cells lose mechano-responsive behavior and exhibit abnormal morphology in high-tension epidermal layers. Together, these findings identify the DP-IF network as a key component of the response to mechanical strain and show that its disruption compromises epidermal homeostasis and contributes to disease pathogenesis.

The immune checkpoint protein PD-L1 plays a pivotal role in tumor immune evasion by binding to PD-1 on immune cells, including T lymphocytes. While the expression and function of PD-L1 have been well studied, the importance of its spatial organization on the cell surface of tumor cells remains poorly understood. In this study, we used super-resolution microscopy combined with biochemical perturbations to investigate the factors regulating PD-L1 clustering and its effects on PD-1 binding and T cell inhibition. We found that PD-L1 is organized into nanoscale clusters at the plasma membrane, with distinct regulatory roles for the actin cytoskeleton, galectin-3, and cholesterol. Disruption of cortical actin increased PD-L1 cluster size, while galectin-3 promoted smaller, denser clusters and increased PD-L1 lateral mobility. Cholesterol depletion reduced PD-L1 cluster size and number and impaired PD-1 binding. These findings indicate that PD-L1 surface organization is collectively regulated by the actin cytoskeleton, galectin-3, and membrane cholesterol within the plasma membrane of tumour cells. Our results provide new insights into the dynamic regulation of PD-L1 and its potential as a therapeutic target in cancer immunotherapy.

Proliferating cells maintain their cytoplasmic density within a narrow range but deviate when entering quiescence or experiencing stress, suggesting active regulation. The mechanisms driving these density adjustments and their impact on cellular function remain unclear. Here, we demonstrate that the conserved cAMP-activated protein kinase A (PKA) is a key regulator of cytoplasmic properties. Inactivation of PKA leads to a drastic increase in cytoplasmic dry mass density and reduced diffusion that depends on the environmental stress response (ESR) transcription factors Msn2/4. This change is mediated by the accumulation of glycogen and trehalose, which have opposing effects on intracellular diffusion. Importantly, the accumulation of these carbohydrates confers stress resistance in distinct ways and independently of their roles as energy sources. Our findings highlight the importance of the biophysical properties of the cytoplasm in stress resistance and the role of glycogen and trehalose in regulating these properties.

O-linked {beta}-N-acetylglucosamine (O-GlcNAc) transferase (OGT) is the sole writer for intracellular O-GlcNAcylation. It catalyzes O-GlcNAcylation of thousands of protein substrates, but relatively less is known about the post-translational modifications that occur on OGT itself. Herein, we demonstrate that OGT is S-palmitoylated at Cys-472 and Cys-477, which is mediated by the S-acyltransferase Zinc Finger DHHC-Type Palmitoyl transferase 14 (zDHHC14) and removed by acyl protein thioesterase 2 (APT2). S-Palmitoylation stabilizes OGT by shunting it away from the lysosomal chaperone-mediated autophagy (CMA) pathway, as S-palmitoylation decreases the interaction between OGT and heat shock cognate 70 kDa protein (HSC70), the CMA chaperone. Via label-free quantitative mass spectrometry, we find that S- palmitoylation elevates the affinity between OGT and protein phosphatase 1 catalytic subunit gamma (PPP1CC), but not PPP1CB. We further demonstrate that S-palmitoylation of OGT augments binding with Yes-associated protein-1 (YAP), a protein that associates with PPP1CC, and subsequently enhances YAP O-GlcNAcylation. Our work unearths S-palmitoylation of OGT and CMA-mediated degradation of lysosomal OGT, the orchestration of which finetunes the activity of key OGT complexes, such as OGT-PPP1CC, and contributes to OGT substrate selectivity.

Proteins that distinguish quiescent cells from other non-proliferative states and actively regulate their return to proliferation remain poorly understood. Here, we combined quantitative proteomics with functional image-based screening to identify regulators of the quiescence-to-proliferation transition. Amongst the functional quiescence signature proteins we identified, we focussed on integrin 11 (ITGA11) which is induced across multiple models of reversible quiescence in distinct cell types and that has low expression in proliferating and senescent cells. Although ITGA11 is dispensable for proliferation of asynchronously cycling cells, it is required for efficient cell-cycle re-entry from quiescence. Mechanistically, ITGA11 promotes YAP accumulation and nuclear localization, thereby sustaining SKP2 expression and p27 degradation during cell cycle re-entry. Depletion of p27, or pharmacological activation of YAP signalling rescues the cell-cycle re-entry defect caused by ITGA11 depletion. Together, these findings identify ITGA11 as a functional quiescence signature protein that couples extracellular matrix sensing to YAP-dependent regulation of the Skp2-p27 axis, revealing a mechanism that controls the transition from quiescence to proliferation.

Label-free Raman imaging of living cells is photon limited: at exposures compatible with cellular dynamics, single-pixel spectra carry about one count per channel on a dominant smooth background. We present an unmixing framework in which the decoder of a physics-constrained autoencoder is restricted to a data-driven spectroscopic dictionary: band centers,widths, and pseudo-Voigt shapes are measured from the dataset and fixed, and the network learns only nonnegative band amplitudes, a smooth B-spline background, and a per-pixel gain.First, on slit-scanning images of HeLa cells (532 nm) the dictionary yields spike-free component spectra that read as band tables, including a resonance-enhanced cytochrome-c-associated component matching literature spectra, and the most stable decomposition against the component number. Second, the dictionary and initialization calibrated at 1 s exposure perline transfer to 100 ms per line (12 s sweeps): cytochrome-c spectral identity survives a single sweep (correlation 0.92) while its map remains photon limited; the dictionary provides spectral physicality, and the transferred initialization prevents a structural collapse that global map correlations miss; in a measurement-derived phantom the dictionary estimator holds thecytochrome-c spectrum to 17-19{degrees} spectral angle at 100 ms, where classical factorizations and free decoders lose it (55-64{degrees}). Estimation on the count-equivalent detector output uses a calibrated shifted-Poisson quasi-likelihood. Third, evaluation must be time matched:correlation against a separately acquired reference saturates through slow specimen drift and acquisition mismatch rather than photon noise, and the self-consistency of learned denoisers is inflated by shared bias; time-matched self-consistency and independent cross-checks areproposed.

Cell shape changes during migration, division, or differentiation require the dynamic regulation of actin network mechanics. Actin crosslinkers are central to this regulation, controlling network connectivity and the transmission of contractile forces. A large diversity of crosslinkers exists, differing in length, domain structure, and binding kinetics, yet why cells deploy specific crosslinkers in a physiological context remains unclear. To bridge this gap, we developed a light-controlled actin crosslinker toolbox spanning three physiologically relevant lengths: ~9 nm (fascin-like), ~16 nm (fimbrin-like), and ~56 nm (alpha-actinin-like). Using magnetic pincher experiments and in silico modelling, we show that short and mid-length crosslinkers dynamically tune cortical stiffness and thickness in a density- and myosin-dependent manner, with short crosslinkers also driving pronounced stress-stiffening as the cortex is deformed. Strikingly, minute-scale activation reveals a length-dependent switch in cell behaviour: short crosslinkers cause cortical delamination, while long ones instead drive cell polarization and symmetry breaking. This switch can be overridden by perturbing actin turnover, which unlocks polarization in mid-length crosslinkers that otherwise delaminate. Crosslinker-induced polarization is not merely a local cortical event: it directs subsequent cell spreading, coupling a nanometre-scale molecular choice to a cell-scale decision about movement. Together, these findings establish a versatile optogenetic platform for manipulating actin crosslinking, and show that the cortex can encode a behavioural switch directly in its material architecture.

The precise formation of synapses ensures the proper wiring and function of nervous systems. Specific synapse formation is controlled by synaptic adhesion molecules, which link pre- and post-synaptic cells. Despite this central role, details of how adhesion molecules organize and signal intracellularly to build core synaptic structures are limited. Here, we identify multiple tyrosine phosphorylation sites on the cytoplasmic tail of the C. elegans SYG-1 synaptic adhesion molecule that are critical to initiate presynapse formation. We determine that SRC-1 and SRC-2 tyrosine kinases are redundantly responsible for SYG-1 phosphorylation and are consequently critical for presynapse assembly. The phosphorylated population of SYG-1 localizes in clusters within a larger SYG-1 pool and these clusters mark sites of presynaptic active zone assembly. Reconstitution of SYG-1 clusters in vitro with SH2-domain adapters and WSP-1 reveals a dynamic biomolecular condensate-forming system. Blocking phosphotyrosine adapters and condensate formation in vivo results in the loss of SYG-1 clusters, defective presynapse formation, and compromised neurotransmission. We conclude that phosphorylation of a subpopulation of synaptic adhesion molecules activates and organizes them into condensate-based clusters to initiate presynapse formation.

Biomolecular condensates (BMCs) organize cellular biochemistry by concentrating selected molecules into dynamic membrane-free compartments. Yet the molecular parameters that determine not only whether condensates form, but also how they behave and what they do, remain poorly defined. Here we show that scaffold binding affinity (Kd) is a quantitative determinant of condensate phase behavior, internal dynamics and biochemical output. Using a modular SUMO-SIM system in which scaffold valency was held constant while binding affinity was systematically varied, we found that affinity governs the phase boundary, resistance to chemical perturbation, and molecular mobility of condensates in vitro and in human cells. In multicomponent mixtures, the highest-affinity scaffold dominated dense-phase composition and dynamics, revealing a hierarchical rule for condensate organization. Finally, affinity-dependent changes in condensate dynamics translated into tunable enzyme activity, establishing binding energetics as an engineerable parameter for programming condensate biochemistry.

Insulin/IGF-1 signaling (IIS) centrally promotes stem/progenitor proliferation during development to translate nutrition into tissue expansion. In adults however, despite ongoing feeding and systemic IIS stimulation, most tissues stop growing. How adult tissues balance out IIS-induced growth is incompletely understood. Here, we report a direct molecular link between IIS and calcium responses that permits a global reduction of germ tissue turnover rates in spermless C. elegans hermaphrodites. We show that these spermless hermaphrodites require the key negative IIS regulator DAF-18/PTEN to prevent AKT-1,2/AKT from phospho-inhibiting the highly conserved small GTPase RHO-1/RHOA in their spermathecal necks to improve their calcium sensitivity. Their increased contractility restricts ovulation and triggers oocyte accumulation along with a concomitant downregulation of GSC proliferation, stabilizing their germline in a hyperplastic state. Similar IIS-calcium cross talks may explain how IIS promotes anabolism in adult tissues without causing their expansion, and why reduced PTEN activity provokes benign differentiated hamartoma-like tumors.

Meso2EM is a correlative light and electron microscopy workflow that transfers neurons selected from mesoscale functional images to targeted electron microscopy. We recorded Ca{superscript 2} signals from layer 2/3 neurons across a contiguous 3 x 3 mm cortical field in awake mice and reidentified a selected neuron after fixation and tangential sectioning. Lectin-labeled vascular architecture served as a shared landmark across in vivo two-photon imaging, confocal microscopy, laboratory micro-CT of resin-embedded tissue, and block-surface scanning electron microscopy, guiding focused-ion-beam scanning electron microscopy to the target cell body. The same progressive-targeting principle also supported serial ATUM-SEM reconstruction of an in vivo-tracked dendrite and serial transmission electron microscopy of optically selected dendrites from a patch-clamp-recorded Martinotti cell. Meso2EM therefore provides a practical route for preserving target identity across large changes in scale and specimen state while restricting electron-microscopy acquisition to a selected region.

MYCN amplification drives replication stress in high-risk neuroblastoma, yet how MYCN-amplified tumour cells tolerate this stress to sustain proliferation remains poorly understood. Here we show that FBXL12, an SCF ubiquitin ligase substrate receptor that targets the Fanconi anaemia protein FANCD2 for degradation at replication forks, as well as the broader Fanconi anaemia and replication stress transcriptional program are elevated in high-risk and MYCN-amplified neuroblastoma. High FBXL12 expression independently predicts poor survival across neuroblastoma patient cohorts. FBXL12 loss stabilizes FANCD2 on chromatin, elevates ATR-dependent replication stress signalling and DNA damage during S phase, and impairs proliferation of MYCN-amplified neuroblastoma cells in vitro and in vivo. Mechanistically, MYCN directly engages the FBXL12-FANCD2 complex and antagonises FBXL12-mediated degradation of FANCD2 at replication forks, revealing that the oncogenic driver of replication stress also actively preserves the chromatin-bound FANCD2 pool required to tolerate it. Beyond S phase, FBXL12 loss disrupts FANCD2-dependent mitotic DNA synthesis and transmits unresolved replication intermediates into daughter cells. FBXL12-deficient cells consequently show transcriptional activation of MYC target gene, ATR, and mTOR signalling programs, and this pathway-concordant state confers differential sensitivity to ATR, and mTOR-targeting compounds, nominating candidate therapeutic strategies for this disease subset. Together, these findings define a MYCN-FBXL12-FANCD2 axis as a clinically relevant vulnerability in high-risk neuroblastoma.

KRAS is one of the most frequently mutated oncoproteins in cancer. Its ability to induce malignant transformation relies on metabolic reprogramming that causes cells to become dependent on aerobic glycolysis as a primary source of energy and for generating biological building blocks. Thus far, the signaling mechanism used by oncogenic KRAS to promote these changes in cancer cell metabolism has not been fully elucidated. However, through studies in pancreatic ductal adenocarcinoma (PDAC) cell lines and patient-derived organoids, we now demonstrate how oncogenic KRAS triggers an increase in glycolytic activity and identify Survivin as a newly discovered and critical KRAS-signaling partner essential for promoting these metabolic changes. We show that oncogenic KRAS potently upregulates the expression of Survivin in PDAC cells and patient-derived organoids undergoing increased glycolysis, whereas depleting Survivin expression inhibits their glycolytic activity and growth. Through a combination of cellular, biochemical, and imaging approaches, we further show that Survivin promotes the formation of unique microtubule-based structures that resemble invadosome rosettes, allowing for the recruitment of the glycolytic enzymes triose phosphate isomerase (TPI) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to these super-structures which drives the increases in glycolysis. These findings demonstrate that by directing the assembly of a microtubule-based complex of metabolic enzymes, Survivin serves as a vital link in a KRAS signaling pathway responsible for promoting the metabolic changes necessary for the accelerated growth of PDAC cells, and thus potentially highlight new therapeutic strategies for treating KRAS-dependent cancers.

Surface phenotyping underpins plant science, preclinical animal research and entomology, yet across all three the measurement is almost always a photograph, which records a projection and not the surface itself. Here we present the Gentschinator3000, an open structured-light platform that brings high-end metric surface measurement within reach of laboratories with no optics expertise, combining documented open hardware, open reconstruction software and analysis workflows for under 4000 Euro in components. It resolves a planar reference to 45 m local flatness, registers full rotations to a loop closure of 156 m, and performs stably across acquisition ranges that we define. Applying one workflow to a leaf before and after desiccation, to murine anatomy and to a spread lepidopteran, we find that projection underestimates surface area by 11 to 41 %. That error grows with the condition under study, with the evaluation scale and with the direction of view, so it can confound phenotype comparisons dramatically. In murine limbs a 15-degree change of viewing direction shifts a projected inter-segment angle by up to 23.2 degrees, while the three-dimensional angle does not move. Projection geometry can therefore contribute as much to a measured phenotype as the biology it is meant to quantify.

X-chromosome inactivation involves chromosome-wide gene silencing accompanied by extensive chromatin changes, as well the loss of topologically associating domains. Yet discrete regions of the inactive X chromosome retain activity within localised 3D domains, which contain active genes that variably escape from X inactivation. The transcription factor and architectural protein CTCF has been proposed to be implicated in escape by insulating escape domains or sustaining their topology via cohesin-mediated loop extrusion. Here, we test the role of CTCF and cohesin in escape using acute degron-mediated depletion of CTCF and RAD21 in neural progenitor cells with established escape profiles. Although CTCF occupancy correlates with escape status on the inactive X chromosome, its removal - together with loss of loop extrusion - does not disrupt escapee gene expression, or domain organization, nor does it result in spreading of silencing or activation of genes in cis. Rather, we show that facultative escape regions are self-sustaining compartments of active chromatin enriched in H3K27 acetylation and depleted in H3K27 methylation, with the magnitude of compartment strength scaling up with the degree of transcriptional activity on the inactive X chromosome. These active escapee compartments are propagated independently of CTCF and RAD21-dependent 3D architecture. Our findings identify chromatin compartmentalization as the primary feature of facultative escapee domains.

Spinal presynaptic inhibitory interneurons are thought to regulate proprioceptive sensory feedback to shape motor output, however, their specific contribution to motor behavior has been difficult to assess, partially due to the lack of a specific genetic handle. Here, we identify Sall3 as the transcription factor required for the establishment and maintenance of GABApre axo-axonic synapses on proprioceptive Ia afferent terminals. Loss of Sall3 in mice selectively eliminates GABApre boutons on Ia afferent terminals, resulting in altered sensory-evoked motor responses and impaired skilled locomotor behaviors. Together, these findings establish Sall3 as a key regulator of GABApre circuit development and provide a genetic framework for understanding how presynaptic inhibition shapes sensorimotor integration.

Replication-associated errors can cause DNA damage to accumulate on the newly synthesized strand over time. In specific cases such as stem cells, retention of the immortal strand used as template preserves one daughter cell into pluripotency while correlating with terminal differentiation of the damage one. In somatic cells, DNA damage distribution after mitosis remains unclear. Here, we uncovered a mechanism of non-random segregation of the DNA damage marker gH2AX occurring during a single cell division cycle. Replication stress using hydroxyurea (HU) upon release into S phase in RPE-1, BJ, hCEC D29 and fibroblasts showed reproducible Non-Random Segregation (NRS) of gH2AX in the ensuing G1, a phenotype not observed in any of the cancer cell lines analyzed. Notably, removal of R-loops led to a reduction of cells with NRS, whether RNaseH1 was over-expressed globally or exclusively targeted to centromeres, indicating that centromeric DNA-RNA hybrids contribute to NRS of the damage. In line with our previous evidence of centromeric chromatin disruption leading to R-loops, rapid removal of the histone H3 variant CENP-A causes damage and NRS, although to a lower extent than HU alone. This implies that additional mechanisms contribute to centromeric R-loops and NRS of damage in the daughter cells upon mitotic exit. Mechanistically, chemical inhibition of the catalytic activity of Rad51 led to a significant drop in NRS without a change in the total amount of damaged cells, implying involvement of the Homologous Recombination (HR) pathway to accumulation of gH2AX to only one chromatid. In turn, this affects the spindle-kinetochore with a measurable length asymmetry, inducing mechanical and/or epigenetic signals that affect the orientation of the sister chromatids on the metaphase plate to bias segregation. Altogether, we found replication-induced asymmetric segregation of DNA damage during mitosis that is influenced by centromeric R-loops, Rad51 activity and spindle dynamics, with implications on cell fate, chromosome and genome stability in the daughter cells.

mRNAs can form stable structures that need to be resolved to facilitate translation. During translation initiation in mammals, the scanning 48S complex requires the helicase activity of DHX29 to unwind stable mRNA structures that cannot be resolved by eIF4A. Here, we show that the yeast DHX29 homolog, Ylr419w (Dhx29), has a similar function during translation on elongating 80S ribosomes. Cryo-EM analyses show that the Dhx29 helicase module is positioned at the mRNA entry channel to engage mRNA, while its double-stranded RNA-binding domain (dsRBD) senses hairpin-forming mRNA in the ribosomal A-site. By selective ribosome profiling, we observed that Dhx29 is associated with transcripts that form RNA structures, such as stable tetraloops. Dhx29 mutants with perturbed helicase activity enrich 80S with hairpins in the A-site, as well as ribosome collisions, while a mutant lacking the N-terminal dsRBD sensor domain loses the specificity for such ribosomes. We thus propose that Dhx29 functions in translation elongation by resolving structured mRNA formed in the ribosomal A-site through its 3'-5' helicase activity and pulling on the mRNA from its 3' end.