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Search indexed bioRxiv preprints in genomics, neuroscience, cell biology and bioinformatics. Read source abstracts and check manuscript versions; preprints are not peer reviewed.

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At least 1,549 records · Page 86Linked to original sources

Structure of E. coli Twin-arginine translocase (Tat) complex with bound cargo

How the twin-arginine translocase (Tat) system transports fully folded substrate proteins across cellular membranes without disrupting membrane integrity has been a fundamental question in cell biology for decades. The Tat system recognizes cargo signal peptide via a conserved twin-arginine motif and is found in prokaryotes and plant organelles. Multi-subunit Tat complex facilitates proton motive force-dependent translocation process, yet its overall architecture remains unknown. Here, we present an atomic cryo-EM structure of a E. coli trimeric TatB3C3 complex bound to the substrate SufI. The complex adopts an unusual wide-open, bowl-shaped architecture with a polar inner cavity. Unexpectedly, the cargo is engaged in a dual-contact mode: while the signal peptide binds inside one TatBC unit, the folded domain docks tightly onto an adjacent unit. The structure offers a mechanistic framework for substrate engagement and translocation by the Tat system, suggesting a direct involvement of the entire Tat complex in substrate translocation.

biochemistry↗

NUCGEN3D: A synthetic framework for large-scale 3D nuclear segmentation with open-source training data and models

AO_SCPLOWBSTRACTC_SCPLOWRobust nuclear segmentation in 3D microscopy images is a critical yet unresolved challenge in quantitative cell biology, hindered by the scarcity and variability of annotated volumetric datasets. Because such data are difficult to obtain, most state-of-the-art approaches, including Cellpose, segment individual 2D slices and then heuristically reconstruct 3D volumes, thereby losing critical spatial context. Our analysis of expert annotator performance confirms that ignoring 3D context introduces substantial variability in nuclear detection and annotation. While a few 3D models have been trained on small or toy datasets, no large-scale, openly available resource currently exists to enable robust training of high-capacity 3D segmentation networks. To address this, we present NucGen3D, a customizable simulation framework that generates large-scale, annotated 3D microscopy datasets from limited 2D input, specifically the 2018 Data Science Bowl dataset. NucGen3D produces realistic 3D volumes across diverse biological and imaging scenarios, including variations in nuclear morphology, spatial arrangement, acquisition artifacts, and imaging noise. Using this synthetic data, we trained two models from scratch: a 2D convolutional neural network under Cellpose-like conditions, and a fully 3D convolutional model that extends the 2D settings. We evaluated both on a challenging, independent real-world dataset with complex nuclear architectures. Both models, especially the 3D model, consistently outperformed state-of-the-art methods, including those trained on larger annotated datasets or based on more complex architectures. These results demonstrate that synthetic data can effectively substitute for real 3D annotations in training performing models at scale. To promote reproducibility and further research, we release both the NucGen3D framework and the fully trained 3D segmentation model as open source, making this the first end-to-end open resource for large-scale 3D nuclear segmentation.

bioinformatics↗

AniMarkerDB: a comprehensive database for exploring cell types and marker genes in livestock and poultry at single-cell resolution

Single-cell RNA sequencing (scRNA-seq) has dramatically advanced the understanding of cellular heterogeneity. While numerous marker gene databases are available for humans and mice, a lack of systematic resources for livestock and poultry species remains, limiting progress in functional genomics, immunology, and breeding.. To address this challenge, we developed AniMarkerDB (https://animarkerdb.bio), a comprehensive and curated database dedicated to marker genes and immune-related epitopes in economically animals, including chicken, pig, and duck. AniMarkerDB integrates 7,010 marker gene across 37 tissues and 846 cell types, together with 71,442 immune epitope records from IEDB. All entries undergo rigorous literature curation, manual validation, and multi-level quality control, with standardized nomenclature and annotation to ensure data consistency and reusability. The platform supports flexible queries by species, tissue, cell type, or gene. It offers analytical tools for cross-species comparison model organisms such as human and mouse, interactive single-cell atlas visualization, and user-defined cell type annotation. Additionally, AniMarkerDB provides dynamic visualizations and export options, enabling researchers to efficiently obtain large-scale marker and epitope data for downstream applications such as infectious disease research, vaccine target design, and comparative immunology. Looking ahead, AniMarkerDB will expand species coverage and incorporate additional modalities, including single-cell atlases from healthy and disease models, establishing itself as a comprehensive and authoritative platform for animal cell biology, disease modeling, and translational research. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/682327v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@af7e7borg.highwire.dtl.DTLVardef@198d114org.highwire.dtl.DTLVardef@1c69ed2org.highwire.dtl.DTLVardef@e4fc43_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

Systematic Discovery of Pathogen Effector Functions across Human Pathogens and Pathways

Pathogens deploy effector proteins to exploit host cell biology, and most pathogen open reading frames (ORFs) are rapidly evolving and lack functional annotation. We developed the eORFeome, a scalable functional genomics platform encompassing 3,835 effector ORFs from diverse viruses, bacteria, and parasites. High-throughput barcoded screens across NF{kappa}B, apoptosis, p53, cGAS-STING and MHC-I pathways revealed functions for hundreds of uncharacterized eORFs, unexpected new activities for known effectors, and distinct pathway-specific functions encoded by single ORFs. Illustrating the power of the approach, we identify HHV6A U14 as a p53 antagonist, HHV7 U21 as a dual-function STING antagonist and MHC-I antigen display inhibitor, and adenoviral 13.6K/i-leader protein as a de novo evolved TAP inhibitor that suppresses MHC-I display. These results establish a general framework for systematic effector annotation, uncover new mechanisms of host-pathogen interaction across kingdoms, and highlight pathogen effectors as a versatile toolkit for rewiring and probing human cellular pathways.

systems biology↗

MANY PATHS TO DESTRUCTION: FAMILY-SPECIFIC TURNOVER AND STRESS RESPONSES FOR TRNA INTRONS

In organisms ranging from Archaea to humans, a subset of genes encoding tRNAs contain introns. Upon splicing, the tRNA exons are joined and the released free introns are rapidly degraded. Although tRNAs introns were previously considered to be "junk" sequences, we recently reported that free tRNA introns (fitRNAs) of S. cerevisiae serve as negative regulators of the cellular levels of mRNAs that bear long stretches of open reading frame sequence complementarity to tRNA introns. We also reported that 2 of the 10 families of tRNA introns, accumulate to elevated levels when cells suffer oxidative stress. The results led to the current investigations of the regulation of tRNA intron cellular levels. We document that tRNA intron turnover occurs by combinations of 5 RNA kinases, 5 to 3 and 3 to 5 exonucleases as well as by at least three endonucleases and, generally, the levels of each tRNA intron family are regulated by a unique combination of nucleases/kinases. Similarly, one family of excised intron can form circles whereas the other free tRNA intron families do not. Further, levels of individual tRNA introns differ in response to environmental conditions including type of media, stage in growth curves, and exposure to elevated temperature. Together, these findings highlight the many cellular pathways utilized to regulate tRNA intron levels and the specificity of these pathways for different tRNA families and varying cellular conditions. The results underscore the likely important roles of the newly discovered individual fitRNAs in regulation of cell biology and responses to environmental conditions.

molecular biology↗

Derivation of primed sheep embryonic stem cells and conversion to an intermediate naive-like state

Embryonic stem cells (ESCs) derived from the inner cell mass of embryos possess unlimited self-renewal and pluripotency, offering a powerful system to study early development and enable genetic and biotechnological innovation. Although several livestock ESC lines have been reported in recent years, defining culture conditions that support stable long-term self-renewal and controlled transitions across pluripotent states remains challenging. Here, we report the de novo derivation of sheep embryonic stem cells (sESCs) from in vivo blastocysts using a chemically defined culture system. The derived cells exhibit morphological and molecular features of primed pluripotency and can be propagated under both feeder-dependent and feeder-free conditions without loss of identity or karyotypic stability. Building on this foundation, we developed enhancer-driven reporter lines that faithfully reflect OCT4 and SOX2 transcriptional activity, enabling dynamic visualization of pluripotency and differentiation in live cultures. These reporter systems revealed the responsiveness of sESCs to signaling modulation and provided a functional readout of pluripotency state transitions. When cultured in defined media previously shown to stabilize naive pluripotency in human ESCs, sESCs adopted dome-shaped colony morphology, maintained OCT4, SOX2, and NANOG expression, retained differentiation potential, and exhibited a transcriptomic profile consistent with resetting to an intermediate pluripotent state with naive-like morphological features. These findings establish stable sheep ESC lines and demonstrate their plasticity across the pluripotency spectrum, providing a valuable platform for investigating ruminant stem cell biology and advancing livestock biotechnology.

developmental biology↗

A multi-center study on factors influencing the reproducibility of in vitro drug-response studies

Evidence that some influential biomedical results cannot be repeated has increased interest in practices that generate data meeting findable, accessible, interoperable and reproducible (FAIR) standards. Multiple papers have identified examples of irreproducibility, but practical steps for increasing reproducibility have not been widely studied. Here, seven research centers in the NIH LINCS Program Consortium investigate the reproducibility of a prototypical perturbational assay: quantifying the responsiveness of cultured cells to anti-cancer drugs. Such assays are important for drug development, studying cell biology, and patient stratification. While many experimental and computational factors have an impact on intra- and inter-center reproducibility, the factors most difficult to identify and correct are those with a strong dependency on biological context. These factors often vary in magnitude with the drug being analyzed and with growth conditions. We provide ways of identifying such context-sensitive factors, thereby advancing the conceptual and practical basis for greater experimental reproducibility.

cancer biology↗

Promoter boundaries for the luxCDABE and betIBA-proXWV operons in Vibrio harveyi defined by the method RAIL: Rapid Arbitrary PCR Insertion Libraries

Experimental studies of transcriptional regulation in bacteria require the ability to precisely measure changes in gene expression, often accomplished through the use of reporter genes. However, the boundaries of promoter sequences required for transcription are often unknown, thus complicating construction of reporters and genetic analysis of transcriptional regulation. Here, we analyze reporter libraries to define the promoter boundaries of the luxCDABE bioluminescence operon and the betIBA-proXWV osmotic stress operon in Vibrio harveyi. We describe a new method called RAIL (Rapid Arbitrary PCR Insertion Libraries) that combines the power of arbitrary PCR and isothermal DNA assembly to rapidly clone promoter fragments of various lengths upstream of reporter genes to generate large libraries. To demonstrate the versatility and efficiency of RAIL, we analyzed the promoters driving expression of the luxCDABE and betIBA-proXWV operons and created libraries of DNA fragments from these loci fused to fluorescent reporters. Using flow cytometry sorting and deep sequencing, we identified the DNA regions necessary and sufficient for maximum gene expression for each promoter. These analyses uncovered previously unknown regulatory sequences and validated known transcription factor binding sites. We applied this high-throughput method to gfp, mCherry, and lacZ reporters and multiple promoters in V. harveyi. We anticipate that the RAIL method will be easily applicable to other model systems for genetic, molecular, and cell biological applications.\n\nImportanceGene reporter constructs have long been essential tools for studying gene regulation in bacteria, particularly following the recent advent of fluorescent gene reporters. We developed a new method that enables efficient construction of promoter fusions to reporter genes to study gene regulation. We demonstrate the versatility of this technique in the model bacterium Vibrio harveyi by constructing promoter libraries for three bacterial promoters using three reporter genes. These libraries can be used to determine the DNA sequences required for gene expression, revealing regulatory elements in promoters. This method is applicable to various model systems and reporter genes for assaying gene expression.

molecular biology↗

RNA sequencing of Stentor cell fragments reveals key processes underlying cellular regeneration

While ciliates of the genus Stentor are known for their ability to regenerate when their cells are damaged or even fragmented, the physical and molecular mechanisms underlying this process are poorly understood. To identify genes involved in the regenerative capability of Stentor cells, RNA sequencing of individual Stentor polymorphus cell fragments was performed. After splitting a cell over the anterior-posterior axis, the posterior fragment has to regenerate the oral apparatus, while the anterior part needs to regenerate the hold fast. Altogether, differential expression analysis of both posterior and anterior S. polymorphus cell fragments for four different post-split time points revealed over 10,000 up-regulated genes throughout the regeneration process. Among these, genes involved in cell signaling, microtubule-based movement and cell cycle regulation seemed to be particularly important during cellular regeneration. We identified roughly nine times as many up-regulated genes in regenerating S. polymorphus posterior fragments as compared to anterior fragments, indicating that regeneration of the anterior oral apparatus is a complex process that involves many genes. Our analyses identified several expanded groups of genes such as dual-specific tyrosine-(Y)-phosphorylation regulated kinases and MORN domain containing proteins that seemingly act as key-regulators of cellular regeneration. In agreement with earlier morphological and cell biological studies, our differential expression analyses indicate that cellular regeneration and vegetative division share many similarities.

genomics↗

Quantitative variation within a species for traits underpinning C4 photosynthesis

Engineering C4 photosynthesis into C3 crops such as rice or wheat could substantially increase their yield by alleviating photorespiratory losses1,2. This objective is challenging because the C4 pathway involves complex modifications to the biochemistry, cell biology and anatomy of leaves3. Forward genetics has provided limited insight into the mechanistic basis of these characteristics and there have been no reports of significant quantitative intra-specific variation of C4 attributes that would allow trait-mapping4,5. Here we show that accessions of C4 Gynandropsis gynandra collected from locations across Africa and Asia exhibit natural variation in key characteristics of C4 photosynthesis. Variable traits include bundle sheath size and vein density, gas exchange parameters and carbon-isotope discrimination associated with the C4 state, but also abundance of transcripts encoding core enzymes of the C4 cycle. Traits relating to water use showed more quantitative variation than those associated with carbon assimilation. We propose variation in these traits likely adapted the hydraulic system for increased water use efficiency rather than improving carbon fixation, indicating that selection pressure may drive C4 diversity in G. gynandra by acting to modify water use rather than photosynthesis. As these accessions can be easily crossed and produce fertile offspring, our findings indicate that natural variation within a C4 species is sufficiently large to allow genetic-mapping of key anatomical C4 traits and regulators.

plant biology↗

Structure and mutagenic analysis of the lipid II flippase MurJ from Escherichia coli

The peptidoglycan cell wall provides an essential protective barrier in almost all bacteria, defining cellular morphology and conferring resistance to osmotic stress and other environmental hazards. The precursor to peptidoglycan, lipid II, is assembled on the inner leaflet of the plasma membrane. However, peptidoglycan polymerization occurs on the outer face of the plasma membrane, and lipid II must be flipped across the membrane by the MurJ protein prior to its use in peptidoglycan synthesis. Due to its central role in cell wall assembly, MurJ is of fundamental importance in microbial cell biology and is a prime target for novel antibiotic development. However, relatively little is known regarding the mechanisms of MurJ function, and structural data are only available for MurJ from the extremophile Thermosipho africanus. Here, we report the crystal structure of substrate-free MurJ from the Gram-negative model organism Escherichia coli, revealing an inward-open conformation. Taking advantage of the genetic tractability of E. coli, we performed high-throughput mutagenesis and next-generation sequencing to assess mutational tolerance at every amino acid in the protein, providing a detailed functional and structural map for the enzyme and identifying sites for inhibitor development. Finally, through the use of sequence co-evolution analysis we identify functionally important interactions in the outward-open state of the protein, supporting a rocker-switch model for lipid II transport.

biochemistry↗

Specific Eph Receptor-Cytoplasmic Effector Signaling Mediated by SAM-SAM Domain Interactions

The Eph receptor tyrosine kinase (RTK) family is the largest subfamily of RTKs playing critical roles in many developmental processes such as tissue patterning, neurogenesis and neuronal circuit formation, angiogenesis, etc. How the 14 Eph proteins, via their highly similar cytoplasmic domains, can transmit diverse and sometimes opposite cellular signals upon engaging ephrins is a major unresolved question. Here we systematically investigated the bindings of each SAM domain of Eph receptors to the SAM domains from SHIP2 and Odin, and uncover a highly specific SAM-SAM interaction-mediated cytoplasmic Eph-effector binding pattern. Comparative X-ray crystallographic studies of several SAM-SAM heterodimer complexes, together with biochemical and cell biology experiments, not only revealed the exquisite specificity code governing Eph/effector interactions but also allowed us to identify SAMD5 as a new Eph binding partner. Finally, these Eph/effector SAM heterodimer structures can explain numerous Eph SAM mutations identified in patients suffering from cancers and other diseases.

biophysics↗

A Bayesian sequential learning framework to parameterise continuum models of melanoma invasion into human skin

We present a novel framework to parameterise a mathematical model of cell invasion that describes how a population of melanoma cells invades into human skin tissue. Using simple experimental data extracted from complex experimental images, we estimate three model parameters:(i) the melanoma cell proliferation rate,{lambda} ; (ii) the melanoma cell diffusivity, D; and (iii){delta} , a constant that determines the rate that melanoma cells degrade the skin tissue. The Bayesian sequential learning frame-work involves a sequence of increasingly-sophisticated experimental data from:(i) a spatially uniform cell proliferation assay; (ii) a two-dimensional circular barrier assay; and, (iii) a three-dimensional invasion assay. The Bayesian sequential learning approach leads to well-defined parameter estimates. In contrast, taking a naive approach that attempts to estimate all parameters from a single set of images from the same experiment fails to produce meaningful results. Overall our approach to inference is simple-to-implement, computationally efficient, and well-suited for many cell biology phenomena that can be described by low dimensional continuum models using ordinary differential equations and partial differential equations. We anticipate that this Bayesian sequential learning framework will be relevant in other biological contexts where it is challenging to extract detailed, quantitative biological measurements from experimental images and so we must rely on using relatively simple measurements from complex images.

biophysics↗

Pathogenic DDX3X mutations impair RNA metabolism and neurogenesis during fetal cortical development

De novo germline mutations in the RNA helicase DDX3X account for 1-3% of unexplained intellectual disability (ID) cases in females, and are associated with autism, brain malformations, and epilepsy. Yet, the developmental and molecular mechanisms by which DDX3X mutations impair brain function are unknown. Here we use human and mouse genetics, and cell biological and biochemical approaches to elucidate mechanisms by which pathogenic DDX3X variants disrupt brain development. We report the largest clinical cohort to date with DDX3X mutations (n=78), demonstrating a striking correlation between recurrent dominant missense mutations, polymicrogyria, and the most severe clinical outcomes. We show that Ddx3x controls cortical development by regulating neuronal generation and migration. Severe DDX3X missense mutations profoundly disrupt RNA helicase activity and induce ectopic RNA-protein granules and aberrant translation in neural progenitors and neurons. Together, our study demonstrates novel mechanisms underlying DDX3X syndrome, and highlights roles for RNA-protein aggregates in the pathogenesis of neurodevelopmental disease.

genetics↗

Nemo-like kinase regulates Progranulin levels in the brain through the microglial endocytosis-lysosomal pathway

Genetic variants in Granulin (GRN), which encodes the secreted glycoprotein Progranulin (PGRN), are associated with several neurodegenerative diseases including frontotemporal lobar degeneration, neuronal ceroid lipofuscinosis, and Alzheimers disease. These genetic alterations manifest in pathological changes due to a reduction of PGRN expression; therefore, identifying a factor that can modulate PGRN levels in vivo would enhance our understanding of PGRN in neurodegeneration, and could reveal novel potential therapeutic targets. Here, we report that Nemo-like kinase (Nlk) regulates Pgrn levels and its associated neuropathophysiology. Genetic interaction studies in mice show that Grn heterozygote mice on an Nlk heterozygote background display pathological and behavioral phenotypes which mimic Grn knockout mice. Furthermore, biochemical and cell biological studies suggest that Nlk reduction promotes Pgrn degradation via the endocytosis-lysosomal pathway, specifically in microglia. Our results reveal a new mechanism for the regulation of Pgrn in the brain and provide insight into the pathophysiology of PGRN-associated diseases.

neuroscience↗

Methanomethylophilus alvus Mx1201 provides basis for mutual orthogonal pyrrolysyl tRNA/aminoacyl-tRNA synthetase pairs in mammalian cells

Genetic code expansion via stop codon suppression is a powerful technique for engineering proteins in mammalian cells with site-specifically encoded non-canonical amino acids (ncAAs). Current methods rely on very few available tRNA/aminoacyl-tRNA synthetase pairs orthogonal in mammalian cells, the pyrrolysyl tRNA/aminoacyl-tRNA synthetase pair from Methanosarcina mazei (Mma PylRS/PylT) being the most active and versatile to date. We found a previously uncharacterized pyrrolysyl tRNA/aminoacyl-tRNA synthetase pair from the human gut archaeon Methanomethylophilus alvus Mx1201 (Mx1201 PylRS/PylT) to be active and orthogonal in mammalian cells. We show that the new PylRS enzyme can be engineered to expand its ncAA substrate spectrum. We find that due to the large evolutionary distance of the two pairs, Mx1201 PylRS/PylT is partially orthogonal to Mma PylRS/PylT. Through rational mutation of Mx1201 PylT, we abolish its non-cognate interaction with Mma PylRS, creating two mutually orthogonal PylRS/PylT pairs. Combined in the same cell, we show that the two pairs can site-selectively introduce two different ncAAs in response to two distinct stop codons. Our work expands the repertoire of mutually orthogonal tools for genetic code expansion in mammalian cells and provides the basis for advanced in vivo protein engineering applications for cell biology and protein production.

synthetic biology↗

MemBright: a Family of Fluorescent Membrane Probes for Advanced Cellular Imaging and Neuroscience

The proper staining of the plasma membrane (PM) is critical in bioimaging as it delimits the cell. Herein, we developed MemBright: a family of six cyanine-based fluorescent turn-on PM probes that emit from orange to near-infrared when reaching the PM, and enable homogeneous and selective PM staining with excellent contrast in mono and two-photon microscopy. These probes are compatible with long-term live cell imaging and immunostaining. Moreover, MemBright label neurons in a brighter manner than surrounding cells allowing identification of neurons in acute brain tissue section and neuromuscular-junctions without any use of transfection or transgenic animals. At last, MemBright were used in super-resolution imaging to unravel the dendritic spines neck. 3D multicolor dSTORM in combination with immunostaining revealed en-passant synapse displaying endogenous glutamate receptors clustered at the axonal-dendritic contact site. MemBright probes thus constitute a universal toolkit for cell biology and neuroscience biomembrane imaging with a variety of microscopy techniques.

neuroscience↗

A nanotube-mediated path to protocell formation

Cellular compartments are membrane-enclosed, spatially distinct microenvironments which confine and protect biochemical reactions in the biological cell. On the early Earth, the autonomous formation of compartments is thought to have led to the encapsulation of nucleotides, thereby satisfying a starting condition for the emergence of life. Recently, surfaces have come into focus as potential platforms for the self-assembly of prebiotic compartments, as significantly enhanced vesicle formation was reported in the presence of solid interfaces. The detailed mechanism of such formation at the mesoscale is still under discussion. We report here on the spontaneous transformation of solid surface-adhered lipid deposits to unilamellar membrane compartments through a straightforward sequence of topological changes, proceeding via a network of interconnected lipid nanotubes. We show that this transformation is entirely driven by surface-free energy minimization and does not require hydrolysis of organic molecules, or external stimuli such as electrical currents or mechanical agitation. The vesicular structures take up and encapsulate their external environment during formation, and can subsequently separate and migrate upon exposure to hydrodynamic flow. This may link, for the first time, the self-directed transition from weakly organized bioamphiphile assemblies on solid surfaces to protocells with secluded internal contents.\n\nSignificanceThe nature of the physical and chemical mechanisms behind the formation, growth and division of the earliest protocells is among the key questions concerning the origin of life. Establishing a simple pathway for the assembly of protocell structures from the primordial soup is a particular challenge. Emerging evidence supporting the assumption that solid surfaces have a governing role in protocell formation has recently expanded the scope, and created new inspiration for investigation. By presenting a physical path from self-assembled amphiphile-based membranes on solid surfaces to spherical single-membrane compartments via a consistent sequence of transformations, solely driven by the materials properties of the interfaces, a direct link between the presence of functional biomolecules and the development of protocells can be established.

biophysics↗