Biology subjects

Lu, T. K.

Publications and source records attributed to Lu, T. K..

At least 19 recordsLinked to original sources

bioRxiv2025

Sourdough starter-inspired living materials grown from probiotic consortia with engineered division-of-labor

Genetic circuits enable precise control over cellular behavior. As circuits become more complex, implementing them within a single cell population becomes difficult. Tasks can instead be distributed in engineered consortia. However, selecting appropriate consortia and harnessing the natural traits of each species for such a division of labor remain unsolved challenges. Here, we report the creation of SINERGY, an engineered synthetic sourdough starter in which functional modules are distributed between the two constituent species. These modules, consisting of sensing, communication, and response, enable in vitro biosensing and in vivo drug delivery and modulate the gut ecosystem in an animal disease model. SINERGY not only preserves the safety and health-promoting properties of the natural components but also endows microbes with programmable functionalities, facilitating broad applications in biomedicine.

synthetic biology↗

bioRxiv2024

Synthetic ratio computation for programming population composition and multicellular morphology

Recent advancements in genetic engineering have provided diverse tools for artificially synthesizing population diversity in both prokaryotic and eukaryotic systems. However, achieving precise control over the ratios of multiple cell types within a population derived from a single founder remains a significant challenge. In this study, we introduce a suite of recombinase-mediated genetic devices designed to achieve accurate population ratio control, enabling the distribution of distinct functionalities across multiple cell types. We systematically evaluated key parameters influencing recombination efficiency and developed data-driven models to reliably predict binary differentiation outcomes. Using these devices, we implemented parallel and series circuit topologies to create user-defined, complex cell fate branching programs. These branching devices facilitated the autonomous differentiation of precision fermentation consortia from a single founder strain, optimizing cell-type ratios for applications such as pigmentation and cellulose degradation. Beyond biomanufacturing, we engineered multicellular aggregates with genetically encoded morphologies by coordinating self-organization through cell adhesion molecules (CAMs). Our work provides a comprehensive characterization of recombinase-based cell fate branching mechanisms and introduces a novel approach for the bottom-up, high-resolution construction of synthetic consortia and multicellular assemblies.

synthetic biology↗

bioRxiv2024

Deep generative models generate mRNA sequences with enhanced translation capacity and stability

Despite the tremendous success of messenger RNA (mRNA) COVID-19 vaccines, the extension of this modality to a broader spectrum of diseases necessitates substantial enhancements, particularly in the design of mRNAs with elevated expression levels and extended durability. Here we present GEMORNA, a deep generative model designed to generate novel mRNA coding sequences (CDSs) and untranslated regions (UTRs) with superior translation capacity, comparable to the sophisticated task of language translation and free-form poetry composition with accurate grammar and semantics. Our AI model was trained on an extensive collection of RNA sequences from diverse families, further enhanced with labeled data to refine its performance. Remarkably, we demonstrate that our AI-generated mRNAs exhibited 8.2-fold and 15.9-fold increases in firefly luciferase expression compared to benchmark mRNAs in two different cell types. Additionally, Our AI- designed COVID-19 mRNA vaccine elicited a 4-fold increase in anti-COVID antibody titer in mice relative to BNT162b2. Furthermore, GEMORNAs versatility extends to circular mRNA design, which we facilitated a 27-fold increase in human erythropoietin protein expression in vivo than a systematically optimized benchmark sequence. We also created circular mRNAs with substantial improvements in expression levels, durability and anti-tumor cell cytotoxicity in mRNA-transduced CAR-T cells compared with an experimentally validated benchmark. In summary, GEMORNA generates novel mRNA sequences with significant performance improvements and has the potential to enable a wide range of therapeutic and vaccine applications.

synthetic biology↗

bioRxiv2022

Frame Editors for Precise, Template-Free Frameshifting

Efficiency and accuracy are paramount in genome editing. While CRISPR-Cas nucleases are efficient at editing target genes, their accuracy is limited because following DNA cleavage by Cas proteins, error-prone repair mechanisms introduce random mutations. Improving the accuracy of CRISPR-Cas by reducing random repairs using DNA- or RNA-based templates can compromise efficiency. To simultaneously improve both editing efficiency and accuracy, we created a frameshifting genome-editing technology by fusing Cas9 with DNA polymerases. These Frame Editors (FEs) introduce precise and controlled frameshifts into target loci via specific DNA repairs near Cas9-induced cleavage loci. We demonstrate two types of FEs: the insertion-inducing frame editor (iFE) and the deletion-inducing frame editor (dFE). For iFE, DNA polymerase beta (POLB) is fused with Cas9, which increases the frequency of 1-bp insertions. For dFE, T4 DNA polymerase (T4pol) is fused with Cas9, which increases the frequency of 1-bp deletions. Both types of FEs reduce the number of random mutations at target loci compared with Cas9. We show that off-target editing can be reduced by substituting Cas9 with high-fidelity variants, such as HiFi Cas9 or LZ3 Cas9. Thus, FEs can introduce frameshifts into target loci with much improved mutation profiles compared with Cas9 alone and without the requirement for template sequences, offering a new strategy for repairing pathogenic frameshifts.

bioengineering↗

bioRxiv2022

Optimization of host cell-compatible, antimicrobial peptides effective against biofilms and clinical isolates of drug-resistant bacteria.

Here, we describe the continued synthetic molecular evolution of a lineage of host-compatible antimicrobial peptides (AMP) intended for the treatment of wounds infected with drug-resistant, biofilm-forming bacteria. The peptides tested are variants of an evolved AMP called D-CONGA, which has excellent antimicrobial activities in vitro and in vivo. In this newest generation of rational D-CONGA variants, we tested multiple sequence-structure-function hypotheses that had not been tested in previous generations. Many of the peptide variants have lower antibacterial activity against Gram-positive or Gram-negative pathogens, especially variants that have altered hydrophobicity, secondary structure potential, or spatial distribution of charged and hydrophobic residues. Thus, D-CONGA is generally well tuned for antimicrobial activity. However, we identified a variant, D-CONGA-Q7, with a polar glutamine inserted into the middle of the sequence, that has higher activity against both planktonic and biofilm-forming bacteria as well as lower cytotoxicity against human fibroblasts. Against clinical isolates of K. pneumoniae, innate resistance to D-CONGA was surprisingly common despite a lack of inducible resistance in P. aeruginosa reported previously. Yet, these same isolates were susceptible to D-CONGA-Q7. D-CONGA-Q7 is much less vulnerable to AMP resistance in Gram-negative bacteria than its predecessor. Consistent with the spirit of synthetic molecular evolution, D-CONGA-Q7 achieved a critical gain-of-function and has a significantly better activity profile.

biochemistry↗

bioRxiv2022

Ingestible capsule for detecting labile inflammatory biomarkers in situ

Transient molecules in the gastrointestinal (GI) tract, such as nitric oxide and hydrogen sulfide, are key signals and mediators of inflammatory bowel disease (IBD). Because these molecules are extremely short-lived in the body, they are difficult to detect. To track these reactive molecules in the GI tract, we have developed a miniaturized device that integrates genetically-engineered probiotic biosensors with a custom-designed photodetector and readout chip. Leveraging the molecular specificity of living sensors, we genetically encoded bacteria to respond to IBD-associated molecules by luminescing. Low-power electronic readout circuits (nanowatt power) integrated into the device convert the light from just 1 L of bacterial culture into a wireless signal. We demonstrate biosensor monitoring in the GI tract of small and large animal models and integration of all components into a sub-1.4 cm3 ingestible form factor capable of supporting wireless communication. The wireless detection of short-lived, disease-associated molecules could support earlier diagnosis of disease than is currently possible, more accurate tracking of disease progression, and more timely communication between patient and their care team supporting remote personalized care.

synthetic biology↗

bioRxiv2021

Cas9-Assisted Biological Containment of a Genetically Engineered Human Commensal Bacterium and Genetic Elements

Sophisticated gene circuits built by synthetic biology can enable bacteria to sense their environment and respond predictably. Biosensing bacteria can potentially probe the human gut microbiome to prevent, diagnose, or treat disease. To provide robust biocontainment for engineered bacteria, we devised a Cas9-assisted auxotrophic biocontainment system combining thymidine auxotrophy, an Engineered Riboregulator (ER) for controlled gene expression, and a CRISPR Device (CD). The CD prevents the engineered bacteria from acquiring thyA via horizontal gene transfer, which would disrupt the biocontainment system, and inhibits the spread of genetic elements by killing bacteria harboring the gene cassette. This system tunably controlled gene expression in the human gut commensal bacterium Bacteroides thetaiotaomicron, prevented escape from thymidine auxotrophy, and blocked transgene dissemination for at least 10 days. These capabilities were validated in vitro and in vivo. This biocontainment system exemplifies a powerful strategy for bringing genetically engineered microorganisms safely into biomedicine.

synthetic biology↗

bioRxiv2021

Ultra-lightweight living structural material for enhanced stiffness and environmental sensing

Natural materials such as bone, wood, and bamboo can inspire the fabrication of stiff, lightweight structural materials. Biofilms are one of the most dominant forms of life in nature. However, little is known about their physical properties as a structural material. Here we report an Escherichia coli biofilm having a Youngs modulus close to 10 GPa with ultra-low density, indicating a high-performance structural material. The mechanical and structural characterization of the biofilm and its components illuminates its adaptable bottom-up design, consisting of lightweight microscale cells covered by a dense network of amyloid nanofibrils on the surface. We engineered E. coli such that 1) carbon nanotubes assembled on the biofilm, enhancing its stiffness to over 30 GPa, or that 2) the biofilm sensitively detected heavy metal as an example of an environmental toxin. These demonstrations offer new opportunities for developing responsive living structural materials to serve many real-world applications.

synthetic biology↗

bioRxiv2021

Sense-and-respond payload delivery using a novel antigen-inducible promoter improves suboptimal CAR-T activation

Chimeric antigen receptor (CAR)-T cell therapies demonstrate the clinical potential of lymphocytes engineered with synthetic properties. However, CAR-T cells are ineffective in most solid tumors, partly due to inadequate activation of the infused lymphocytes at the site of malignancy. To selectively enhance anti-tumor efficacy without exacerbating off-target toxicities, CAR-T cells can be engineered to preferentially deliver immunostimulatory payloads in tumors. Here, we report a novel antigen-inducible promoter and single-vector sense-and-respond circuit for conditional payload expression in primary human T cells. In therapeutic T cell models, the novel NR4A-based promoter induced higher transgene expression than the conventional NFAT-based promoter under weakly immunogenic conditions, where payload expression is most needed. Minimal activity was detected from the inducible promoters in the absence of antigen and after withdrawal of stimulation. As a functional proof-of-concept, we used the NR4A-based promoter to express cytokines in an anti-mesothelin CAR-T model with suboptimal stimulation, and observed improved proliferation compared to T cells engineered with the conventional NFAT promoter or CAR alone. Our single-vector circuit achieves CAR-directed payload expression under weakly immunogenic conditions and could enable the next generation of cell therapies with enhanced anti-tumor efficacy.

synthetic biology↗

bioRxiv2020

A Synthetic Transcription Platform for Programmable Gene Expression in Mammalian Cells

Precise, scalable, and sustainable control of genetic and cellular activities in mammalian cells is key to developing precision therapeutics and smart biomanufacturing. We created a highly tunable, modular, versatile CRISPR-based synthetic transcription system for the programmable control of gene expression and cellular phenotypes in mammalian cells. Genetic circuits consisting of well-characterized libraries of guide RNAs, binding motifs of synthetic operators, transcriptional activators, and additional genetic regulatory elements expressed mammalian genes in a highly predictable and tunable manner. We demonstrated the programmable control of reporter genes episomally and chromosomally, with up to 25-fold more activity than seen with the EF1 promoter, in multiple cell types. We used these circuits to program the secretion of human monoclonal antibodies and to control T-cell effector function marked by interferon-{gamma} production. Antibody titers and interferon-{gamma} concentrations significantly correlated with synthetic promoter strengths, providing a platform for programming gene expression and cellular function in diverse applications.

synthetic biology↗

bioRxiv2020

Antigen-specific induction of CD4+CD8αα+ intraepithelial T lymphocytes byBacteroidetes species

The microbiome contributes to the development and maturation of the immune system1-3 In response to commensal bacteria, CD4+ T cells can differentiate into distinct functional subtypes with regulatory or effector functions along the intestine. Peripherally-induced Foxp3+-regulatory T cells (pTregs) maintain immune homeostasis at the intestinal mucosa by regulating effector T cell responses against dietary antigens and microbes4. Similarly to pTregs, a subset of small intestine intraepithelial lymphocytes CD4+CD8+ (CD4IELS) exhibit regulatory properties and promote tolerance against dietary antigens5. Development of CD4IELS from conventional CD4+ T cells or from Treg precursors depends on the microbiota5,6. However, the identity of the microbial antigens recognized by CD4IELs remains unknown. We identified species belonging to the Bacteroidetes phylum as commensal bacteria capable of generating CD4IEL from naive CD4+ T cells expressing the pTreg transnuclear (TN) monoclonal TCR6 as well as from polyclonal WT T cells. We found that {beta}-hexosaminidase, a widely conserved carbohydrate-metabolizing enzyme in the Bacteroidetes phylum, is recognized by TN T cells, which share their TCR specificity with CD4+ T cells found in the intraepithelial compartment of polyclonal specific-pathogen-free (SPF) mice. In a mouse model of colitis, {beta}-hexosaminidase-specific CD4IELs provided protection from ulceration of the colon and weight loss. Thus, a single T cell clone can recognize a variety of abundant commensal bacteria and elicit a regulatory immune response at the intestinal epithelial surface.

immunology↗

bioRxiv2020

Natural combinatorial genetics and prolific polyamine production enable siderophore diversification in Serratia plymuthica

Siderophores are small molecules with unmatched capacity to scavenge iron from proteins and the extracellular milieu, where it mostly occurs as insoluble Fe3+. Siderophores chelate Fe3+ for uptake into the cell, where it is reduced to soluble Fe2+. As iron is essential for bacterial survival, siderophores are key molecules in low soluble iron conditions. Bacteria have devised many strategies to synthesize proprietary siderophores to avoid siderophore piracy by competing organisms, e.g., by incorporating different polyamine backbones into siderophores, while maintaining the catechol moieties. We report that Serratia plymuthica V4 produces a variety of siderophores, which we term the siderome, and which are assembled by the concerted action of enzymes encoded in two independent gene clusters. Besides assembling serratiochelin with diaminopropane, S. plymuthica utilizes putrescine and the same set of enzymes to assemble photobactin, a siderophore described for Photorhabdus luminescens. The enzymes encoded by one of the gene clusters can independently assemble enterobactin. A third, independent operon is responsible for biosynthesis of the hydroxamate siderophore aerobactin, initially described in Enterobacter aerogenes. Mutant strains not synthesizing polyamine-siderophores significantly increased enterobactin production levels, though lack of enterobactin did not impact serratiochelin production. Knocking out SchF0, an enzyme involved in the assembly of enterobactin alone, significantly reduced bacterial fitness. This study illuminates the interplay between siderophore biosynthetic pathways and polyamine production superpathways, indicating routes of molecular diversification. Given its natural yields of diaminopropane (97.75 μmol/g DW) and putrescine (30.83 μmol/g DW), S. plymuthica can be exploited for the industrial production of these compounds.Significance Statement Siderophores are molecules crucial for bacterial survival in low iron environments. Bacteria have evolved the capacity to pirate siderophores made by other bacterial strains and to diversify the structure of their own siderophores, to prevent piracy. We found that Serratia plymuthica V4 produces five different siderophores using three gene clusters and a polyamine production superpathway. The most well studied siderophore, enterobactin, rather than the strain’s proprietary and by far most abundant siderophore, serratiochelin, displayed a crucial role in the fitness of S. plymuthica. Our results also indicate that this strain is a good candidate for engineering the large-scale production of diaminopropane (DAP), as without any optimization it produced the highest amounts of DAP reported for wild-type strains.Competing Interest StatementT.K.L. is a co-founder of Senti Biosciences, Synlogic, Engine Biosciences, Tango Therapeutics, Corvium, BiomX, and Eligo Biosciences. T.K.L. also holds financial interests in nest.bio, Ampliphi, IndieBio, MedicusTek, Quark Biosciences, and Personal Genomics.View Full Text

molecular biology↗

bioRxiv2020

Scalable recombinase-based gene expression cascades

Temporal modulation of multiple genes underlies sophisticated biological phenomena. However, there are few scalable and generalizable gene circuit architectures for the programming of sequential genetic perturbations. We describe a modular recombinase-based gene circuit architecture, comprising tandem gene perturbation cassettes (GPCs), that enables the sequential expression of multiple genes in a defined temporal order by alternating treatment with just two orthogonal ligands. We used tandem GPCs to sequentially express single-guide RNAs to encode transcriptional cascades and trigger the sequential accumulation of mutations. We built an all-in-one gene circuit that sequentially edits genomic loci, synchronizes cells at a specific stage within a gene expression cascade, and deletes itself for safety. Tandem GPCs offer a multi-tiered cellular programming tool for modeling multi-stage genetic changes, such as tumorigenesis and cellular differentiation.Competing Interest StatementThe authors have declared no competing interest.View Full Text

synthetic biology↗

bioRxiv2020

Multiplex CRISPRi-Cas9 silencing of planktonic and stage-specific biofilm genes in Enterococcus faecalis

Enterococcus faecalis is an opportunistic pathogen, which can cause multidrug-resistant life-threatening infections. Gaining a complete understanding of enterococcal pathogenesis is a crucial step in identifying a strategy to effectively treat enterococcal infections. However, bacterial pathogenesis is a complex process often involving a combination of genes and multi-level regulation. Compared to established knockout methodologies, CRISPRi approaches enable rapid and efficient silencing of genes to interrogate gene products and pathways involved in pathogenesis. As opposed to traditional gene inactivation approaches, CRISPRi can also be quickly repurposed for multiplexing or used to study essential genes. Here we have developed a novel dual-vector nisin-inducible CRISPRi system in E. faecalis that can efficiently silence via both non-template and template strand targeting. Since nisin-controlled gene expression system is functional in various Gram-positive bacteria, the developed CRISPRi tool can be extended to other genera. This system can be applied to study essential genes, genes involved in antimicrobial resistance, and genes involved in biofilm formation and persistence. The system is robust, and can be scaled up for high-throughput screens or combinatorial targeting. This tool substantially enhances our ability to study enterococcal biology and pathogenesis, host-bacteria interactions, and inter-species communication. IMPORTANCEEnterococcus faecalis causes multidrug resistant life-threatening infections, and is often co-isolated with other pathogenic bacteria from polymicrobial biofilm-associated infections. Genetic tools to dissect complex interactions in mixed microbial communities are largely limited to transposon mutagenesis and traditional time- and labour-intensive allelic exchange methods. Built upon streptococcal dCas9, we developed an easily-modifiable, inducible CRISPRi system for E. faecalis that can efficiently silence single and multiple genes. This system can silence genes involved in biofilm formation, antibiotic resistance, and can be used to interrogate gene essentiality. Uniquely, this tool is optimized to study genes important for biofilm initiation, maturation, and maintenance, and can be used to perturb pre-formed biofilms. This system will be valuable to rapidly and efficiently investigate a wide range of aspects of complex enterococcal biology.

microbiology↗

bioRxiv2020

High-throughput CRISPR screens to dissect macrophage-Shigella interactions

Shigellosis causes most diarrheal deaths worldwide, particularly affecting children. Shigella invades and replicates in the epithelium of the large intestine, eliciting inflammation and tissue destruction. To understand how Shigella rewires macrophages prior to epithelium invasion, we performed genome-wide and focused secondary CRISPR knockout and CRISPR interference (CRISPRi) screens in Shigella flexneri-infected human monocytic THP-1 cells. Knockdown of the Toll-like receptor 1/2 signaling pathway significantly reduced pro-inflammatory cytokine and chemokine production, enhanced host cell survival, and controlled intracellular pathogen growth. Knockdown of the enzymatic component of the mitochondrial pyruvate dehydrogenase complex enhanced THP-1 cell survival. Small molecule inhibitors blocking key components of these pathways had similar effects; these were validated with human monocyte-derived macrophages, which closely mimic the in vivo physiological state of cells post-infection. High-throughput CRISPR screens can elucidate how S. flexneri triggers inflammation and redirects host pyruvate catabolism for energy acquisition before killing macrophages, pointing to new shigellosis therapies.

microbiology↗

bioRxiv2020

Illuminating host-mycobacterial interactions with functional genomic screening to inhibit mycobacterial pathogenesis

Existing antibiotics are inadequate to defeat tuberculosis (TB), a leading cause of death worldwide. We sought potential targets for host-directed therapies (HDTs) by investigating the host immune response to mycobacterial infection. We used CRISPR/Cas9-mediated high-throughput genetic screens to identify perturbations that improve the survival of human phagocytic cells infected with Mycobacterium bovis BCG (Bacillus Calmette-Guerin), as a proxy for Mycobacterium tuberculosis (Mtb). Many of these perturbations constrained the growth of intracellular mycobacteria. We identified over 100 genes associated with diverse biological pathways as potential HDT targets. We validated key components of the type I interferon and aryl hydrocarbon receptor signaling pathways that respond to the small-molecule inhibitors cerdulatinib and CH223191, respectively; these inhibitors enhanced human macrophage survival and limited the intracellular growth of Mtb. Thus, high-throughput functional genomic screens can elucidate highly complex host-pathogen interactions and serve to identify HDTs with the potential to improve TB treatment.

microbiology↗

bioRxiv2020

High-Throughput 5' UTR Engineering for Enhanced Protein Production in Non-Viral Gene Therapies

Despite significant clinical progress in cell and gene therapies, maximizing protein expression in order to enhance potency remains a major challenge. One approach to increase protein expression is by optimizing translation through the engineering of 5 untranslated regions (5 UTRs). Here, we developed a high-throughput strategy to design, screen, and optimize novel 5UTRs that enhance protein expression from a strong human cytomegalovirus (CMV) promoter. We first identified naturally occurring 5 UTRs with high translation efficiencies and used this information with in silico genetic algorithms to generate synthetic 5 UTRs. A total of [~]12,000 5 UTRs were then screened using a recombinase-mediated integration strategy that greatly enhances the sensitivity of high-throughput screens by eliminating copy number and position effects that limit lentiviral approaches. Using this approach, we identified three synthetic 5 UTRs that outperformed commonly used non-viral gene therapy plasmids in expressing protein payloads. Furthermore, combinatorial assembly of these 5 UTRs enabled even higher protein expression than obtained with each individual 5 UTR. In summary, we demonstrate that high-throughput screening of 5 UTR libraries with recombinase-mediated integration can identify genetic elements that enhance protein expression, which should have numerous applications for engineered cell and gene therapies.

synthetic biology↗

bioRxiv2020

High throughput functional variant screens via in-vivo production of single-stranded DNA

Tremendous genetic variation exists in nature, but our ability to create and characterize individual genetic variants remains far more limited in scale. Likewise, engineering proteins and phenotypes requires the introduction of synthetic variants, but design of variants outpaces experimental measurement of variant effect. Here, we optimize efficient and continuous generation of precise genomic edits in Escherichia coli, via in-vivo production of single-stranded DNA by the targeted reverse-transcription activity of retrons. Greater than 90% editing efficiency can be obtained using this method, enabling multiplexed applications. We introduce Retron Library Recombineering (RLR), a system for high-throughput screens of variants, wherein the association of introduced edits with their retron elements enables a targeted deep sequencing phenotypic output. We use RLR for pooled, quantitative phenotyping of synthesized variants, characterizing antibiotic resistance alleles. We also perform RLR using sheared genomic DNA of an evolved bacterium, experimentally querying millions of sequences for antibiotic resistance variants. In doing so, we demonstrate that RLR is uniquely suited to utilize non-designed sources of variation. Pooled experiments using ssDNA produced in vivo thus present new avenues for exploring variation, both designed and not, across the entire genome.

synthetic biology↗