Rxivist combines preprints from bioRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 83,702 bioRxiv papers from 360,579 authors.
Most downloaded bioRxiv papers, all time
in category synthetic biology
765 results found. For more information, click each entry to expand.
1,502 downloads synthetic biology
The RNA-guided DNA endonuclease Cas9 has emerged as a powerful new tool for genome engineering. Cas9 creates targeted double-strand breaks (DSBs) in the genome. Knock-in of specific mutations (precision genome editing) requires homology-directed repair (HDR) of the DSB by synthetic donor DNAs containing the desired edits, but HDR has been reported to be variably efficient. Here, we report that linear DNAs (single and double-stranded) engage in a high-efficiency HDR mechanism that requires only ~35 nucleotides of homology with the targeted locus to introduce edits ranging from 1 to 1000 nucleotides. We demonstrate the utility of linear donors by introducing fluorescent protein tags in human cells and mouse embryos using PCR fragments. We find that repair is local, polarity-sensitive, and prone to template switching, characteristics that are consistent with gene conversion by synthesis-dependent strand-annealing (SDSA). Our findings enable rational design of synthetic donor DNAs for efficient genome editing.
1,468 downloads synthetic biology
Inflammation in the gut, caused by infection and autoimmunity, remains challenging to effectively detect, monitor, and treat. Here, we engineer a commensal mouse E. coli strain to record exposure to tetrathionate, a downstream product of reactive oxygen species generated during inflammation. Using these programmed bacteria to sense in situ levels we show that tetrathionate accompanies inflammation during Salmonella-induced colitis in mice and is elevated in an inflammatory bowel disease mouse model. We demonstrate long-term genetic stability and associated robust function of synthetic genetic circuits in bacteria colonizing the mammalian gut. These results demonstrate the potential for engineered bacteria to stably and reliably probe pathophysiological processes for which traditional diagnostics may not be feasible or cost-effective.
1,458 downloads synthetic biology
In mammalian cells, transient gene expression (TGE) is a rapid, minimal-investment alternative to single-copy integrations for testing of transgenic constructs. However, transient gene expression, as measured by flow cytometry with a fluorescent reporter, typically displays a broad, asymmetric distribution with a left-tail that is convolved with background signal. Common approaches for deriving a summary statistic for transiently expressed gene products impose a normal distribution on gated or ungated data. Summary statistics derived from these models are heavily biased by experimental conditions and instrument settings that are difficult to replicate and insufficient to accurately describe the underlying data. Here, we present a convolved gamma distribution as a superior model for TGE datasets. The 4-6 parameters of this model are sufficient to accurately describe the entire, ungated distribution of transiently transfected HEK cells expressing monomeric fluorescent proteins, that operates consistently across a range of transfection conditions and instrument settings. Based on these observations, a convolved gamma model of TGE distributions has the potential to significantly improve the accuracy and reproducibility of genetic device characterization in mammalian cells.
1,456 downloads synthetic biology
Gene synthesis, the process of assembling gene-length fragments from shorter groups of oligonucleotides (oligos), is becoming an increasingly important tool in molecular and synthetic biology. The length, quality, and cost of gene synthesis is limited by errors produced during oligo synthesis and subsequent assembly. Enzymatic error correction methods are cost-effective means to ameliorate errors in gene synthesis. Previous analyses of these methods relied on cloning and Sanger sequencing to evaluate their efficiencies, limiting quantitative assessment and throughput. Here we develop a method to quantify errors in synthetic DNA by next-generation sequencing. We analyzed errors in a model gene assembly and systematically compared six different error correction enzymes across 11 conditions. We find that ErrASE and T7 Endonuclease I are the most effective at decreasing average error rates (up to 5.8-fold relative to the input), whereas MutS is the best for increasing the number of perfect assemblies (up to 25.2-fold). We are able to quantify differential specificities such as ErrASE preferentially corrects C/G → G/C transversions whereas T7 Endonuclease I preferentially corrects A/T → T/A transversions. More generally, this experimental and computational pipeline is a fast, scalable, and extensible way to analyze errors in gene assemblies, to profile error correction methods, and to benchmark DNA synthesis methods.
1,450 downloads synthetic biology
Recording biological signals can be difficult in three-dimensional matrices, such as tissue. We present a DNA polymerase-based strategy that records temporal biosignals locally onto DNA to be read out later, which could obviate the need to extract information from tissue on the fly. We use a template-independent DNA polymerase, terminal deoxynucleotidyl transferase (TdT) that probabilistically adds dNTPs to single-stranded DNA (ssDNA) substrates without a template. We show that in vitro , the dNTP-incorporation preference of TdT changes with the presence of Co2+, Ca2+, Zn2+ and temperature. Extracting the signal profile over time is possible by examining the dNTP incorporation preference along the length of synthesized ssDNA strands like a molecular ticker tape. We call this TdT-based untemplated recording of temporal local environmental signals (TURTLES). We show that we can determine the time of Co2+ addition to within two minutes over a 60-minute period. Further, TURTLES has the capability to record multiple fluctuations. We can estimate the rise and fall of an input Co2+ pulse to within three minutes. TURTLES has at least 200-fold better temporal resolution than all previous DNA-based recording techniques.
1,447 downloads synthetic biology
We employ a reporter assay and SHAPE-seq to study translational regulation by RNA-binding proteins, in bacteria. For the reporter assay, we designed 50 constructs, each with a single hairpin based on the binding sites of the RNA-binding coat proteins of phages MS2, PP7, GA, and Qβ, at various positions within the N-terminus of a reporter gene. In the absence of RNA-binding proteins, the translation level depends on the position of the hairpin, and exhibits three-nucleotide periodicity. For hairpin positions within the initiation region, in the presence of cognate RNA-binding protein, we observe strong translational repression. In vivo SHAPE-seq results for a representative construct indicate that repression correlates with protection of both the hairpin and the ribosome binding site. Our data suggest that the RBP- hairpin complex entraps the 30S subunit, thereby stalling initiation. We utilize the repression phenomenon in a high-throughput assay for quantitative study of protein-RNA binding in vivo.
1,446 downloads synthetic biology
We describe a synthetic genetic circuit for controlling asymmetric cell division in E. coli in which a progenitor cell creates a differentiated daughter cell while retaining its original phenotype. Specifically, we engineered an inducible system that can bind and segregate plasmid DNA to a single position in the cell. Upon cell division, co-localized plasmids are kept by one and only one of the daughter cells. The other daughter cell receives no plasmid DNA and is hence irreversibly differentiated from its sibling. In this way, we achieved asymmetric cell division through asymmetric plasmid partitioning. We then used this system to achieve physical separation of genetically distinct cells by tying motility to differentiation. Finally, we characterized an orthogonal inducible circuit that enables the simultaneous asymmetric partitioning of two plasmid species, resulting in cells that have four distinct differentiated states. These results point the way towards engineering multicellular systems from prokaryotic hosts.
1,433 downloads synthetic biology
Intracellular protein copy numbers show significant cell-to-cell variability within an isogenic population due to the random nature of biological reactions. Here we show how the variability in copy number can be controlled by perturbing gene expression. Depending on the genetic network and host, different perturbations can be applied to control variability. To understand more fully how noise propagates and behaves in biochemical networks we developed stochastic control analysis (SCA) which is a sensitivity-based analysis framework for the study of noise control. Here we apply SCA to synthetic gene expression systems encoded on plasmids that are transformed into Escherichia coli. We show that (1) dual control of transcription and translation efficiencies provides the most efficient way of noise-vs.-mean control. (2) The expressed proteins follow the gamma distribution function as found in chromosomal proteins. (3) One of the major sources of noise, leading to the cell-to-cell variability in protein copy numbers, is related to bursty translation. (4) By taking into account stochastic fluctuations in autofluorescence, the correct scaling relationship between the noise and mean levels of the protein copy numbers was recovered for the case of weak fluorescence signals.
1,399 downloads synthetic biology
The construction of complex gene regulatory networks requires both inhibitory and up-regulatory modules. However, the vast majority of RNA-based regulatory “parts” are inhibitory. Using a synthetic biology approach combined with SHAPE-Seq, we explored the regulatory effect of RBP-RNA interactions in bacterial 5’-UTRs. By positioning a library of RNA hairpins upstream of a reporter gene and co-expressing them with the matching RBP, we observed a set of regulatory responses, including translational stimulation, translational repression, and cooperative behavior. Our combined approach revealed three distinct states in-vivo : in the absence of RBPs, the RNA molecules can be found either in a molten state that is amenable to translation, or a structured phase that inhibits translation. In the presence of RBPs, the RNA molecules are in a semi-structured phase with partial translational capacity. Our work provides new insight into RBP-based regulation and a blueprint for designing complete gene regulatory circuits at the post-transcriptional level.
1,379 downloads synthetic biology
In this study, an Escherichia coli (E. coli) based transcription translation cell-free system (TX-TL) was employed to sample various enzyme expression levels of the violacein pathway. The pathway was successfully reconstructed in TX-TL. Its variation produced different metabolites as evident from the extracts assorted colors. Analysis of the violacein product via UV-Vis absorption and liquid chromatography-mass spectrometry (LC-MS) detected 68 nanograms of violacein per 10 microliters reaction volume. Significant buildup of prodeoxyviolacein intermediate was also detected in the equimolar TX-TL reaction. Finally, design space exploration experiments suggested an improvement in violacein production at high VioC and VioD DNA concentrations.
1,376 downloads synthetic biology
Multiplexed assays allow functional testing of large synthetic libraries of genetic elements, but are limited by the designability, length, fidelity and scale of the input DNA. Here we improve DropSynth, a low-cost, multiplexed method which builds gene libraries by compartmentalizing and assembling microarray-derived oligos in vortexed emulsions. By optimizing enzyme choice, adding enzymatic error correction, and increasing scale, we show that DropSynth can build thousands of gene-length fragments at >20% fidelity.
1,373 downloads synthetic biology
Multi-part DNA assembly is the physical starting point for many projects in Synthetic and Molecular Biology. The ability to explore a genetic design space by building extensive libraries of DNA constructs is essential for creating programmed biological systems that perform the desired functions. With multiple DNA assembly methods and standards adopted in the Synthetic Biology community, automation of the DNA assembly process has received serious attention in recent years. Importantly, automating DNA assembly enables larger builds using less researcher time, increasing the accessible design space. However, these benefits currently incur high costs for both equipment and consumables. Here, we address this limitation by introducing low-cost DNA assembly with BASIC on OpenTrons (DNA-BOT). For this purpose, we developed an open-source software package dnabot (https://github.com/BASIC- DNA-ASSEMBLY/dnabot). We demonstrate the performance of DNA-BOT by simultaneously assembling 88 constructs composed of 10 genetic parts, exploring the promoter, ribosome binding site (RBS) and gene order design space for a 3-gene operon. All 88 constructs were assembled with high accuracy, at a cost of $1.50 - $5.50 per construct. This illustrates the efficiency, accuracy and affordability of DNA-BOT making it accessible for most labs and democratising automated DNA assembly.
1,366 downloads synthetic biology
Point mutations underlie many genetic diseases. In this regard, while programmable DNA nucleases have been used to repair mutations, their use for gene therapy poses multiple challenges: one, efficiency of homologous recombination is typically low in cells; two, an active nuclease presents a risk of introducing permanent off-target mutations; and three, prevalent programmable nucleases typically comprise elements of non-human origin raising the potential of in vivo immunogenicity. In light of these, approaches to instead directly target RNA, and use of molecular machinery native to the host would be highly desirable. Towards this, we engineered and optimized two complementary approaches, referred together hereon as tRiAD, based on the use of tRNAs in codon suppression and adenosine deaminases in RNA editing. Specifically, by delivering modified endogenous tRNAs and/or the RNA editing enzyme ADAR2 and an associated guiding RNA (adRNA) via adeno-associated viruses, we enabled premature stop codon read-through and correction in the mdx mouse model of muscular dystrophy that harbors a nonsense mutation in the dystrophin gene. We further demonstrated inducible restoration of dystrophin expression by pyrolysyl-tRNA mediated incorporation of unnatural amino acids (UAAs) at the stop codon. Additionally, we also engineered ADAR2 mediated correction of a point mutation in liver RNA of the spfash mouse model of ornithine transcarbamylase (OTC) deficiency. Taken together, our results establish the use of suppressor tRNAs and ADAR2 for in vivo RNA targeting, and this integrated tRiAD approach is robust, genomically scarless, and potentially non-immunogenic as it utilizes effector RNAs and human proteins.
1,360 downloads synthetic biology
Gene drives may be capable of addressing ecological problems by altering entire populations of wild organisms, but their use has remained largely theoretical due to technical constraints. Here we consider the potential for RNA-guided gene drives based on the CRISPR nuclease Cas9 to serve as a general method for spreading altered traits through wild populations over many generations. We detail likely capabilities, discuss limitations, and provide novel precautionary strategies to control the spread of gene drives and reverse genomic changes. The ability to edit populations of sexual species would offer substantial benefits to humanity and the environment. For example, RNA-guided gene drives could potentially prevent the spread of disease, support agriculture by reversing pesticide and herbicide resistance in insects and weeds, and control damaging invasive species. However, the possibility of unwanted ecological effects and near-certainty of spread across political borders demand careful assessment of each potential application. We call for thoughtful, inclusive, and well-informed public discussions to explore the responsible use of this currently theoretical technology.
1,335 downloads synthetic biology
G protein-coupled receptor (GPCR) signaling is the primary method eukaryotes use to respond to specific cues in their environment. However, the relationship between stimulus and response for each GPCR is difficult to predict due to diversity in natural signal transduction architecture and expression. Using genome engineering in yeast, we here constructed an insulated, modular GPCR signal transduction system to study how the response to stimuli can be predictably tuned using synthetic tools. We delineated the contributions of a minimal set of key components via computational and experimental refactoring, identifying simple design principles for rationally tuning the dose-response. Using four different receptors, we demonstrate how this enables cells and consortia to be engineered to respond to desired concentrations of peptides, metabolites and hormones relevant to human health. This work enables rational tuning of cell sensing, while providing a framework to guide reprogramming of GPCR-based signaling in more complex systems.
1,334 downloads synthetic biology
Immunotherapies such as checkpoint inhibitors have revolutionized cancer therapy yet lead to a multitude of immune-related adverse events, suggesting the need for more targeted delivery systems. Due to their preferential colonization of tumors and advances in engineering capabilities from synthetic biology, microbes are a natural platform for the local delivery of cancer therapeutics. Here, we present an engineered probiotic bacteria system for the controlled production and release of novel immune checkpoint targeting nanobodies from within tumors. Specifically, we engineered genetic lysis circuit variants to effectively release nanobodies and safely control bacteria populations. To maximize therapeutic efficacy of the system, we used computational modeling coupled with experimental validation of circuit dynamics and found that lower copy number variants provide optimal nanobody release. Thus, we subsequently integrated the lysis circuit operon into the genome of a probiotic E. coli Nissle 1917, and confirmed lysis dynamics in a syngeneic mouse model using in vivo bioluminescent imaging. Expressing a nanobody against PD-L1 in this strain demonstrated enhanced efficacy compared to a plasmid-based lysing variant, and similar efficacy to a clinically relevant monoclonal antibody against PD-L1. Expanding upon this therapeutic platform, we produced a nanobody against cytotoxic T-lymphocyte associated protein -4 (CTLA-4), which reduced growth rate or completely cleared tumors when combined with a probiotically-expressed PD-L1 nanobody in multiple syngeneic mouse models. Together, these results demonstrate that our engineered probiotic system combines innovations in synthetic biology and immunotherapy to improve upon the delivery of checkpoint inhibitors.
1,311 downloads synthetic biology
Current methods for assembling metabolic pathways require a process of repeated trial and error and have a long design-build-test cycle. Further, it remains a challenge to precisely tune enzyme expression levels for maximizing target metabolite production. Recently it was shown that a cell-free transcriptional-translation system (TX-TL) can be used to rapidly prototype novel complex biocircuits as well as metabolic pathways. TX-TL systems allow protein expression from multiple DNA pieces, opening up the possibility of modulating concentrations of DNA encoding individual pathway enzymes and testing the related effect on metabolite production. In this work, we demonstrate TX-TL as a platform for exploring the design space of metabolic pathways using a 1,4-BDO biosynthesis pathway as an example. Using TX-TL, we verified enzyme expression and enzyme activity and identified the conversion of 4-hydroxybutyrate to downstream metabolites as a limiting step of the 1,4-BDO pathway. We further tested combinations of various enzyme expression levels and found increasing downstream enzyme expression levels improved 1,4-BDO production.
1,309 downloads synthetic biology
Vibrio natriegens has recently emerged as an alternative to Escherichia coli for molecular biology and biotechnology, but low-efficiency genetic tools hamper its development. Here, we uncover how to induce natural competence in V. natriegens and describe methods for multiplex genome editing by natural transformation (MuGENT). MuGENT promotes integration of multiple genome edits at high-efficiency on unprecedented timescales. Also, this method allows for generating highly complex mutant populations, which can be exploited for metabolic engineering efforts. As a proof-of-concept, we attempted to enhance production of the value added chemical poly-β-hydroxybutyrate (PHB) in V. natriegens by targeting the expression of nine genes involved in PHB biosynthesis via MuGENT. Within 1 week, we isolated edited strains that produced ~100 times more PHB than the parent isolate and ~3.3 times more than a rationally designed strain. Thus, the methods described here should extend the utility of this species for diverse academic and industrial applications.
1,285 downloads synthetic biology
The dynamics of the bacterial population that comprises the gut microbiota plays key roles in overall mammalian health. However, a detailed understanding of bacterial growth within the gut is limited by the inherent complexity and inaccessibility of the gut environment. Here, we deploy an improved synthetic genetic oscillator to investigate dynamics of bacterial colonization and growth in the mammalian gut under both healthy and disease conditions. The synthetic oscillator, when introduced into both Escherichia coli and Salmonella Typhimurium maintains regular oscillations with a constant period in generations across growth conditions. We determine the phase of oscillation from individual bacteria using image analysis of resultant colonies and thereby infer the number of cell divisions elapsed. In doing so, we demonstrate robust functionality and controllability of the oscillator circuit's activity during bacterial growth in vitro, in a simulated murine gut microfluidic environment, and in vivo within the mouse gut. We determine different dynamics of bacterial colonization and growth in the gut under normal and inflammatory conditions. Our results show that a precise genetic oscillator can function in a complex environment and reveal single cell behavior under diverse conditions where disease may create otherwise impossible-to-quantify variability in growth across the population.
1,277 downloads synthetic biology
Over the past few years, tools that make use of the Cas9 nuclease have led to many breakthroughs, including in the control of gene expression. The catalytically dead variant of Cas9 known as dCas9 can be guided by small RNAs to block transcription of target genes, in a strategy also known as CRISPRi. Here, we reveal that the level of complementarity between the guide RNA and the target controls the rate at which dCas9 successfully blocks the RNA polymerase. We use this mechanism to precisely and robustly reduce gene expression by defined relative amounts. We demonstrate broad applicability of this method to the study of genetic regulation and cellular physiology. First, we characterize feedback strength of a model auto-repressor. Second, we study the impact of copy-number variations of cell-wall synthesizing enzymes on cell morphology. Finally, we demonstrate that this system can be multiplexed to obtain any combination of fractional repression of two genes.
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