Biology subjects

Liu, X.

Publications and source records attributed to Liu, X..

At least 667 records · Page 37Linked to original sources

bioRxiv2024

De novo Design of A Fusion Protein Tool for GPCR Research

G protein-coupled receptors (GPCRs) play pivotal roles in cellular signaling and represent prominent drug targets. Structural elucidation of GPCRs is crucial for drug discovery efforts. However, structural studies of GPCRs remain challenging, particularly for inactive state structures, which often require extensive protein engineering. Here, we present a de novo design strategy termed "click fusion" for generating fusion proteins to facilitate GPCR structural studies. Our method involves the rational design of structurally stable protein domains rigidly linked to GPCRs. The resulting fusion protein enhances the thermostability of the target GPCR and aids in determining GPCR structures via cryo-electron microscopy (cryo-EM). We further demonstrate that the designed fusion protein can be transferred among structurally similar GPCRs with minor adjustments to the linker region. Our study introduces a promising approach for facilitating GPCR structural studies and advancing drug discovery efforts.

biophysics↗

bioRxiv2024

Rapid production of modified cattle and sheep from spermatid-like stem cells

Genome-modified ruminants, such as cattle and sheep, are important germplasm for agricultural applications. Haploid androgenetic stem cells (haSCs) can support the full-term development of embryos upon intracytoplasmic haSCs injection (iCHI) into intact oocytes. Thus, haSCs are invaluable resources for studying economic traits and significantly impact livestock breeding; however, ruminant haSCs have yet to be obtained. Here, we report the derivation of cattle and sheep haSCs using a recombinant FACE medium. These cells display characteristics of formative-state pluripotency and can differentiate into three germ layers, both in vitro and in vivo. Interestingly, the ectopic expression of protamine in haSCs converts their nuclei into a spermatid-like structure and synergistic enhancement of full-term development of iCHI embryos, named as Pro-iCHI approach. Furthermore, gene-modified cattle and sheep can be efficiently produced through the combinatorial use of the CRISPR and Pro-iCHI approach. Overall, Pro-iCHI provides an easy-to-manipulate agrobiotechnology tool for rapidly producing genetically modified livestock.

bioengineering↗

bioRxiv2024

DRED: A Comprehensive Database of Genes Related to Repeat Expansion Diseases

Expansion of tandem repeats in genes often causes severe neuromuscular diseases, such as fragile X syndrome, huntingtons disease, and spinocerebellar ataxia. However, information on genes associated with repeat expansion diseases is scattered throughout the literature, systematic prediction of potential genes that may cause diseases via repeat expansion is also lacking. Here, we develop DRED, a Database of genes related to Repeat Expansion Diseases, as a manually-curated database that covers all known 61 genes related to repeat expansion diseases reported in PubMed and OMIM, along with detailed repeat information for each gene. DRED also includes 516 genes with the potential to cause diseases via repeat expansion, which were predicted basing on their repeat composition, genetic variations, genomic features, and disease associations. Various types of information on repeat expansion diseases and their corresponding genes/repeats are presented in DRED, together with links to external resources, such as NCBI and ClinVar. DRED provides user-friendly interfaces with comprehensive functions, and can serve as a central data resource for basic research and repeat expansion disease-related medical diagnosis. DRED is freely accessible at http://omicslab.genetics.ac.cn/dred, and is frequently updated to include newly reported genes related to repeat expansion diseases.

bioinformatics↗

bioRxiv2024

Cost-benefit analysis across smallholder rice farmers reveals that existing fertilization practices severely compromise their income

Modernizing agricultural practices of smallholder farmers can increase considerably global food produce. Smallholder farmers are, nevertheless, often unwilling to adopt practices unfamiliar to them. Increases in the cost of fertilizers, can nonetheless render existing practices unsustainable, raising concerns of food injustice. We addressed here the potential to which we can increase yield through popularizing existing best practice agricultural approaches. We worked over a network of 40 smallholder farmers in the Danxia Mountain region, Guangdong province, China. We divided them into two crop-rotation treatments and gave them the freedom to implement agricultural management practices the way they usually do. We subsequently clustered them into three groups based on the management history. Over the final growth season, on which the clustering was based, there was an over 30% increase in crop yield between the most and the least efficient clusters. More importantly we show that the use of fertilizers not only did not promote rice production but it also had adverse effects. We finally present a cost-benefit analysis. Through familiarizing of the smallholder farmers existing management practices, policy makers could make integrating new farming guidelines easier to adopt than purely dishing out modern farming practice recommendations. We thus propose that any attempts to transition agricultural practices should involve the extensive monitoring of existing practices at the very beginning. This should effectively close existing yield gaps in relation to industrial farmers.

ecology↗

bioRxiv2024

Intranasal parainfluenza virus-vectored vaccine expressing SARS-CoV-2 spike protein of Delta or Omicron B.1.1.529 induces mucosal and systemic immunity and protects hamsters against homologous and heterologous challenge

The continuous emergence of new SARS-CoV-2 variants requires that COVID vaccines be updated to match circulating strains. We generated B/HPIV3-vectored vaccines expressing 6P-stabilized S protein of the ancestral, B.1.617.2/Delta, or B.1.1.529/Omicron variants as pediatric vaccines for intranasal immunization against HPIV3 and SARS-CoV-2 and characterized these in hamsters. Following intranasal immunization, these B/HPIV3 vectors replicated in the upper and lower respiratory tract and induced mucosal and serum anti-S IgA and IgG. B/HPIV3 expressing ancestral or B.1.617.2/Delta-derived S-6P induced serum antibodies that effectively neutralized SARS-CoV-2 of the ancestral and B.1.617.2/Delta lineages, while the cross-neutralizing potency of B.1.1.529/Omicron S-induced antibodies was lower. Despite the lower cross-neutralizing titers induced by B/HPIV3 expressing S-6P from B.1.1.529/Omicron, a single intranasal dose of all three versions of B/HPIV3 vectors was protective against matched or heterologous WA1/2020, B.1.617.2/Delta or BA.1 (B.1.1.529.1)/Omicron challenge; hamsters were protected from challenge virus replication in the lungs, while low levels of challenge virus were detectable in the upper respiratory tract of a small number of animals. Immunization also protected against lung inflammatory response after challenge, with mild inflammatory cytokine induction associated with the slightly lower level of cross-protection of WA1/2020 and B.1.617.2/Delta variants against the BA.1/Omicron variant. Serum antibodies elicited by all vaccine candidates were broadly reactive against 20 antigenic variants, but the antigenic breadth of antibodies elicited by B/HPIV3-expressed S-6P from the ancestral or B.1.617.2/Delta variant exceeded that of the S-6P B.1.1.529/Omicron expressing vector. These results will guide development of intranasal B/HPIV3 vectors with S antigens matching circulating SARS-CoV-2 variants. Author SummaryIntranasal COVID vaccines have the potential to stimulate respiratory mucosal immunity, effectively restricting replication of SARS-CoV-2 in the respiratory tract, thereby reducing virus shedding and transmission. To develop pediatric vaccines for intranasal immunization against HPIV3 and SARS-CoV-2, we use live-attenuated bovine-human parainfluenza virus vaccine, a pediatric intranasal parainfluenza virus vaccine candidate, designed to express the stabilized SARS-CoV-2 spike protein. We compared the immunogenicity and breadth of protection of the B/HPIV3-expressed ancestral, B.1.617.2/Delta, or B.1.1.529/Omicron variants following intranasal immunization in hamsters. All three B/HPIV3 vectors replicated in the respiratory tract, induced mucosal and serum anti-S IgA and IgG, and were protective in the hamster model against matched or heterologous WA1/2020, B.1.617.2/Delta or BA.1 (B.1.1.529.1)/Omicron SARS-CoV-2 challenge. Serum antibodies elicited by all intranasal vaccine candidates were broadly reactive against 20 antigenic variants of SARS-CoV-2, but the antigenic breadth of antibodies elicited by B/HPIV3-expressed stabilized S from the ancestral or B.1.617.2/Delta variant exceeded that of the S-6P B.1.1.529/Omicron expressing vector. Thus, these intranasal vectored SARS-CoV-2 vaccine candidates induce cross-protective SARS-CoV-2 immunity with antigenic breadth similar to that of injectable SARS-CoV-2 vaccines. These results will guide development of intranasal COVID vaccines based on B/HPIV3 vectors with S antigens matching current SARS-CoV-2 variants.

microbiology↗

bioRxiv2024

Improving Functional Muscle Regeneration in Volumetric Muscle Loss Injuries by Shifting the Balance of Inflammatory and Pro-Resolving Lipid Mediators

Severe tissue loss resulting from extremity trauma, such as volumetric muscle loss (VML), poses significant clinical challenges for both general and military populations. VML disrupts the endogenous tissue repair mechanisms, resulting in acute and unresolved chronic inflammation and immune cell presence, impaired muscle healing, scar tissue formation, persistent pain, and permanent functional deficits. The aberrant healing response is preceded by acute inflammation and immune cell infiltration which does not resolve. We analyzed the biosynthesis of inflammatory and specialized pro-resolving lipid mediators (SPMs) after VML injury in two different models; muscle with critical-sized defects had a decreased capacity to biosynthesize SPMs, leading to dysregulated and persistent inflammation. We developed a modular poly(ethylene glycol)-maleimide hydrogel platform to locally release a stable isomer of Resolvin D1 (AT-RvD1) and promote endogenous pathways of inflammation resolution in the two muscle models. The local delivery of AT-RvD1 enhanced muscle regeneration, improved muscle function, and reduced pain sensitivity after VML by promoting molecular and cellular resolution of inflammation. These findings provide new insights into the pathogenesis of VML and establish a pro-resolving hydrogel therapeutic as a promising strategy for promoting functional muscle regeneration after traumatic injury.

bioengineering↗

bioRxiv2024

Small mammals in biodiversity hotspot harbor viruses of epidemic potential

Metagenomic sequencing has transformed our understanding of viral diversity in wildlife and its threat to human health. Despite this progress, many studies have lacked systematic and ecologically informed sampling, which has left numerous potentially emergent viruses undiscovered, and the drivers of their ecology and evolution poorly understood. We conducted an extensive analysis of viruses in the lung, spleen, and gut of 1,688 animals from 38 mammalian species across 428 sites in Yunnan, China--a hotspot for zoonotic diseases. We identified 162 mammalian viral species, including 102 novel species and 24 posing potential risks to humans due to their relationships with known pathogens associated with serious diseases and their ability to cross major host species barriers. Our findings offer an in-depth view of virus organotropism, cross-species transmission, host sharing patterns, and the ecological factors influencing viral evolution, all of which are critical for anticipating and mitigating future zoonotic outbreaks.

microbiology↗

bioRxiv2024

EPOP Restricts PRC2.1 Targeting to Chromatin by Directly Modulating Enzyme Complex Dimerization

Polycomb repressive complex 2 (PRC2) mediates developmental gene repression as two classes of holocomplexes, PRC2.1 and PRC2.2. EPOP is an accessory subunit specific to PRC2.1, which also contains PCL proteins. Unlike other accessory subunits that collectively facilitate PRC2 targeting, EPOP was implicated in an enigmatic inhibitory role, together with its interactor Elongin BC. We report an unusual molecular mechanism whereby EPOP regulates PRC2.1 by directly modulating its oligomerization state. EPOP disrupts the PRC2.1 dimer and weakens its chromatin association, likely by disabling the avidity effect conferred by the dimeric complex. Congruently, an EPOP mutant specifically defective in PRC2 binding enhances genome-wide enrichments of MTF2 and H3K27me3 in mouse epiblast-like cells. Elongin BC is largely dispensable for the EPOP-mediated inhibition of PRC2.1. EPOP defines a distinct subclass of PRC2.1, which uniquely maintains an epigenetic program by preventing the over-repression of key gene regulators along the continuum of early differentiation.

molecular biology↗

bioRxiv2024

Neural Circuit Underlying Individual differences in Visual Escape Habituation

Emotions, like fear, are internal states enabling organisms to effectively confront environmental threats. When repeatedly exposed to predators, individuals show divergent adaptive responses. However, the neural circuit mechanisms underlying individual differences in to repeated threats remain largely unknown. Here, we identify two distinct types of visual escape--consistent escape (T1) and rapid habituation (T2) -- with unambiguous arousal states to repetitive threat stimuli. We systematically investigate distinct pathways originating from the superior colliculus (SC) and insula that project to the basolateral amygdala (BLA), with relay stations in the mediodorsal thalamus (MD) and ventral tegmental area (VTA), mediating T1 and T2 behavioral types. Additionally, we identify the MD as a critical hub integrating SC and insula inputs, projecting to the BLA and contributing to reduced arousal and attenuated defensive behaviors against looming stimuli. Our findings offer significant insights into the mechanisms of internal states, arousal modulation, and behavioral adaptability. O_FIG O_LINKSMALLFIG WIDTH=178 HEIGHT=200 SRC="FIGDIR/small/611366v1_ufig1.gif" ALT="Figure 1"> View larger version (77K): org.highwire.dtl.DTLVardef@164df34org.highwire.dtl.DTLVardef@17a01e6org.highwire.dtl.DTLVardef@112de44org.highwire.dtl.DTLVardef@1be6aea_HPS_FORMAT_FIGEXP M_FIG Graph Abstract C_FIG In briefWe identify two distinct visual escape behaviors--consistent escape (T1) and rapid habituation (T2)--linked to unique SC and insula pathways projecting to the BLA via MD and VTA. The MD acts as a hub integrating sensory inputs to modulate arousal and defensive responses. These findings advance our understanding of the neural mechanisms driving internal states, arousal modulation, and behavioral adaptability. Highlights[bullet] We identify two distinct visual escape behaviors with unambiguous arousal states--consistent escape (T1) and rapid habituation (T2) --to repeated looming stimuli. [bullet]The SC-VTA-BLA pathway mediated T1 behavioral type, while the SC-MD-BLA pathway mediated T2 type. [bullet]MD as a central hub integrating SC and insula inputs to modulate arousal and defensive behavioral adaptation.

neuroscience↗

bioRxiv2024

A 15-Gene prognostic signature with TFAP2B functioning in Platinum Resistance of Ovarian Carcinoma

Resistance to platinum is the main challenge in the chemotherapy of ovarian cancer (OV). Therefore, developing a response signature to platinum is essential for the precision therapy of OV. Existing quantitative signatures of platinum are susceptible to batch effects and sequencing platform variations. To address this, we developed a transcriptome-based platinum signature, named PRSM, consisting of 15 genes, based on within-sample prognostic and relative expression ordering of genes, to predict individual responses to platinum in OV. The PRSM model demonstrated superior classification accuracy compared to previous quantitative signatures. Resistant samples classified by PRSM exhibited poorer overall survival, lower SNV neoantigen load, tumor mutational burden, and distinct methylation patterns compared to sensitive samples. Pathway analysis revealed the activation of MYC targets V2 and oxidative phosphorylation in resistant tumors. Single-cell analysis highlighted the roles of NK and epithelial cells in resistance. Among the 15 core genes, five (TFAP2B, KRT81, PAGE1, CRNN, UGT2B17) were linked to poor prognosis, with TFAP2B having the highest contribution to PRSM. Overexpression of TFAP2B in A2780 cells enhanced cisplatin sensitivity, while in A2780cis cells, it inhibited growth. In brief, our findings provide a multi-dimensional view of platinum resistance in ovarian cancer, introducing a robust predictive model and identifying potential therapeutic targets.

pharmacology and toxicology↗

bioRxiv2024

Osterix Facilitates Osteocytic Communication by Targeting Connexin43

Osteocytes, terminal-differentiated cells in bone, are now considered as more pivotal regulators of mature bone homeostasis than other bone cells, since they constitute 90- 95% of the bone cell population. Given their non-migratory nature within the mineralized matrix, their unique dendrites are crucial for cell-to-cell communication in response to both intracellular and extracellular stimuli, such as bone fracture or mechanical load. Here, we showed that Osterix (Osx), usually recognized as a specific doorkeeper for osteoblast differentiation during new bone formation marked by collagen type I 1 (Col11), was unexpectedly co-expressed with Col11 in osteocytes within the cortical bone of mice. Deleting Osx in Col11-positive osteocytes disrupted cortical bone structure and osteocytic dendrites in mice, thus impairing transcellular fluid flow and intercellular communication. Conversely, overexpression of Osx in osteocytes enhanced these processes. Furthermore, we identified Connexin43, a critical protein of gap junction channel, was a direct transcriptional target of Osx in regulating dendrites of osteocytes. Pharmacological restoration of Connexin43 levels rescued the dysfunction in Osx-deficient osteocytes both in vitro and in vivo. Taken together, this work demonstrated Osxs distinct role in osteocyte function through maintaining intercellular signaling, which broadened the current understanding of its role in Col11-positive bone cells, extending beyond osteoblasts and bone mineralization, offering new insights into bone diseases such as fracture nonunion or disuse osteoporosis.

cell biology↗

bioRxiv2024

Coat protein of TCV suppresses RNA decay via ubiquitination and autophagy pathways to facilitate viral infection

Highlight statementThe findings highlight that TCV manipulates 26S proteasome and autophagy pathways to obstruct antiviral RNA decay defenses and ultimately enhance its ability to infect host cells. RNA decay is a pervasive process in eukaryotic cells. Viruses utilize the host cells intracellular machinery to gain access to essential molecules and subcellular structures required for infection during the pathogenesis process. The study demonstrates that turnip crinkle virus (TCV) infection enhances the expression of Arabidopsis Dcp1 (AtDcp1), which negatively regulates the accumulation of TCV RNA, indicating its involvement in antiviral defense. Nevertheless, TCV circumvents the antiviral defense based on RNA decay, as indicated by the capsid protein (CP) of TCV stabilizing the known nonsense-mediated RNA decay targeted transcripts. In vivo, CP physically interacts with AtDcp1, promoting AtDcp1 degradation via ubiquitination and autophagy pathways. This is evidenced by the observation that the degradation is inhibited by both 26S proteasome and autophagy inhibitors. Furthermore, CP elevates the polyubiquitination of Dcp1-Flag and the quantity of pre-autophagosome or autophagosome structures. These data indicate that CP suppresses RNA decay by interacting with AtDcp1 and mediating its degradation through the 26S proteasome and autophagy pathways, effectively subduing antiviral RNA decay. This study uncovers a previously unidentified virulence strategy in the ongoing conflict between plants and viruses.

pathology↗

bioRxiv2024

IL-6 and IL-27 negatively regulate CRTAM-expressing CD4+ T-cells associated with lymphoid-driven synovitis.

ABSTRACT-Joint pathology in rheumatoid arthritis is heterogeneous, with histology providing evidence of fibroblast-driven, myeloid-driven, and lymphoid-driven synovitis. However, the immuno-modulatory pathways underlying their development remain unclear. Profiling synovial tissues from rheumatoid arthritis patients and mice with antigen-induced arthritis, we identified a subset of synovial infiltrating CD4+ T-cells expressing CRTAM (class-I MHC-restricted T-cell-associated molecule). In human synovial biopsies, CRTAM correlated with the expression of effector cytokines (IL21, IFNG), chemokine receptors (CXCR3, CXCR4, CCR5), granzymes (GZMA, GZMB, GZMK), and regulatory factors (TIGIT, EOMES, BATF) linked with T-cell-mediated immunity. Studies of antigen-induced arthritis showed that CRTAM+CD4+ T-cells accumulate in the inflamed synovium following disease onset. CRTAM+CD4+ T-cells were particularly abundant in synovial tissue from Il27ra-/- mice displaying ectopic lymphoid-like structures. CADM1 (cell adhesion molecule-1), the endogenous ligand for CRTAM, was also expressed in human synovitis and synovial tissues from wild-type, Il6ra-/-, and Il27ra-/- mice with antigen-induced arthritis. Cells expressing human CADM1 included synovial fibroblasts and subsets of monocytic and CD19+ cells. Considering the ex vivo regulation of CRTAM, we identified that activation of naive CD4+ T-cell increased CRTAM expression. This induction was blocked by IL-6 and IL-27, with further studies identifying a role for STAT3 in controlling the CRTAM transcriptional repressor, ZEB1. These results provide insights into the cytokine control of CRTAM on CD4+ T-cells and support the involvement of CRTAM+CD4+ T-cells in lymphoid-driven synovitis.

immunology↗

bioRxiv2024

Inactivation of necroptosis-promoting protein MLKL creates a therapeutic vulnerability in colorectal cancer cells.

Mortality from colorectal cancer (CRC) is significant, and novel CRC therapies are needed. A pseudokinase MLKL typically executes necroptotic cell death, and MLKL inactivation protects cells from such death. However, we found unexpectedly that MLKL gene knockout enhanced CRC cell death caused by a protein synthesis inhibitor homoharringtonine used for chronic myeloid leukemia treatment. In an effort to explain this finding, we observed that MLKL gene knockout reduced CRC cell autophagy and rendered such autophagy critically dependent on the presence of VPS37A, a component of the ESCRT-I complex. Moreover, homoharringtonine-induced activation of p38 MAP kinase (p38MAPK) prevented VPS37A from supporting autophagy in MLKL-deficient cells and triggered their parthanatos, a cell death type driven by poly(ADP-ribose) polymerase hyperactivation. Finally, a pharmacological MLKL inhibitor necrosulfonamide strongly cooperated with homoharringtonine in suppressing CRC cell tumorigenicity in mice. Thus, while MLKL mediates necroptosis, MLKL protects CRC cells from death caused by drugs blocking basal autophagy, e.g., homoharringtonine, and MLKL inhibition creates a therapeutic vulnerability that could be utilized for CRC treatment.

cancer biology↗

bioRxiv2024

Cis-regulatory elements driving motor neuron-restricted viral payload expression within the mammalian spinal cord

Spinal motor neuron (MN) dysfunction is the cause of a number of clinically significant movement disorders. Despite the recent approval of gene therapeutics targeting these MN-related disorders, there are no viral delivery mechanisms that achieve MN-restricted transgene expression. In this study, chromatin accessibility profiling of genetically defined mouse MNs was used to identify candidate cis-regulatory elements (CREs) capable of driving MN-selective gene expression. Subsequent testing of these candidates identified two CREs that confer MN-selective gene expression in the spinal cord as well as reduced off-target expression in dorsal root ganglia. Within one of these candidate elements, we identified a compact core transcription factor (TF)-binding region that drives MN-selective gene expression. Finally, we demonstrate that selective spinal cord expression of this mouse CRE is preserved in non-human primates. These findings suggest that the generation of cell-type-selective viral reagents, in which cell-type-selective CREs drive restricted gene expression, will be valuable research tools in mice and other mammalian species, with potentially significant therapeutic value in humans. SIGNIFICANCE STATEMENTMotor neurons transduce the motor outputs of nervous system activity to muscle and are the vulnerable neurons in a number of clinically significant degenerative conditions, including spinal muscular atrophy and amyotrophic lateral sclerosis. A recent strategy for treating motor neuron degenerative diseases has been to use viruses to introduce genes into motor neurons to inhibit the degenerative process. However, we still lack viral reagents that promote gene expression in motor neurons without potentially toxic off-target expression in other cell types. Our study identifies cis-regulatory elements capable of conferring motor neuron-selective transgene expression in a viral context. These findings have important implications for future gene therapeutics for motor neuron-related disorders.

neuroscience↗

bioRxiv2024

Automatic diagnostics of electroencephalography pathology based on multi-domain feature fusion

Electroencephalography (EEG) serves as a practical auxiliary tool deployed to diagnose diverse brain-related disorders owing to its exceptional temporal resolution, non-invasive characteristics, and cost-effectiveness. In recent years, with the advancement of machine learning, automated EEG pathology diagnostics methods have flourished. However, most existing methods usually neglect the crucial spatial correlations in multi-channel EEG signals and the potential complementary information among different domain features, both of which are keys to improving discrimination performance. In addition, latent redundant and irrelevant features may cause overfitting, increased model complexity, and other issues. In response, we propose a novel feature-based framework designed to improve the diagnostic accuracy of multi-channel EEG pathology. This framework first applies a multi-resolution decomposition technique and a statistical feature extractor to construct a salient time-frequency feature space. Then, spatial distribution information is channel-wise extracted from this space to fuse with time-frequency features, thereby leveraging their complementarity to the fullest extent. Furthermore, to eliminate the redundancy and irrelevancy, a two-step dimension reduction strategy, including a lightweight multi-view time-frequency feature aggregation and a non-parametric statistical significance analysis, is devised to pick out the features with stronger discriminative ability. Comprehensive examinations of the Temple University Hospital Abnormal EEG Corpus V. 2.0.0 demonstrate that our proposal outperforms state-of-the-art methods, highlighting its significant potential in clinically automated EEG abnormality detection.

bioengineering↗

bioRxiv2024

High-throughput DNA engineering by mating bacteria

To reduce the operational friction and scale DNA engineering, we report here an in vivo DNA assembly technology platform called SCRIVENER (Sequential Conjugation and Recombination for In Vivo Elongation of Nucleotides with low ERrors). SCRIVENER combines bacterial conjugation, in vivo DNA cutting, and in vivo homologous recombination to seamlessly stitch blocks of DNA together by mating E. coli in large arrays or pools. This workflow is simpler, cheaper, and higher throughput than current DNA assembly approaches that require DNA to be moved in and out of cells at different procedural steps. We perform over 5,000 assemblies with two to 13 DNA blocks that range from 240 bp to 8 kb and show that SCRIVENER is capable of assembling constructs as long as 23 kb at relatively high throughput and fidelity. Most SCRIVENER errors are deletions between long interspersed repeats. However, SCRIVENER can overcome these errors by enabling assembly and sequence verification at high replication at a nominal additional cost per replicate. We show that SCRIVENER can be used to build combinatorial libraries in arrays or pools, and that DNA blocks onboarded into the platform can be repurposed and reused with any other DNA block in high throughput without a PCR step. Because of these features, DNA engineering with SCRIVENER has the potential to accelerate design-build-test-learn cycles of DNA products.

synthetic biology↗

bioRxiv2024

DNA flexibility regulates transcription factor binding to nucleosomes

Cell fate decisions are controlled by sequence-specific transcription factors (TFs), referred to as pioneer factors, that bind their target sites within nucleosomes (pioneer binding) and thus initiate chromatin opening. However, pioneers bind just a minority of their recognition sequences present in the genome, suggesting that local sequence context features may regulate pioneer binding. Here, we developed PIONEAR-seq, a highly parallel sequencing-based biochemical assay for high-throughput analysis of TF binding to nucleosomes on nucleosome positioning sequences. Using PIONEAR-seq, we characterized the pioneer binding of 7 human pioneer TFs. Comparison of TF binding to nucleosomes based on the synthetic Widom 601 (W601) model sequence versus three different genomic sequences revealed that the positional preferences of these TFs binding to nucleosomes (i.e., dyad, periodic and end binding) is determined by the broader sequence context of the nucleosome, rather than being a property intrinsic to the TF. We propose a model where the flexibility and rigidity within nucleosomal DNA regulate where pioneers bind within nucleosomes. Our results suggest that the broader physical properties of nucleosomal DNA represent another layer of cis-regulatory information read out by TFs in eukaryotic genomes.

molecular biology↗