51
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Ba F, Liu Y, Liu WQ, Tian X, Li J. SYMBIOSIS: synthetic manipulable biobricks via orthogonal serine integrase systems. Nucleic Acids Res 2022; 50:2973-2985. [PMID: 35191490 PMCID: PMC8934643 DOI: 10.1093/nar/gkac124] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 02/04/2022] [Accepted: 02/09/2022] [Indexed: 11/14/2022] Open
Abstract
Serine integrases are emerging as one of the most powerful biological tools for synthetic biology. They have been widely used across genome engineering and genetic circuit design. However, developing serine integrase-based tools for directly/precisely manipulating synthetic biobricks is still missing. Here, we report SYMBIOSIS, a versatile method that can robustly manipulate DNA parts in vivo and in vitro. First, we propose a 'keys match locks' model to demonstrate that three orthogonal serine integrases are able to irreversibly and stably switch on seven synthetic biobricks with high accuracy in vivo. Then, we demonstrate that purified integrases can facilitate the assembly of 'donor' and 'acceptor' plasmids in vitro to construct composite plasmids. Finally, we use SYMBIOSIS to assemble different chromoprotein genes and create novel colored Escherichia coli. We anticipate that our SYMBIOSIS strategy will accelerate synthetic biobrick manipulation, genetic circuit design and multiple plasmid assembly for synthetic biology with broad potential applications.
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Affiliation(s)
- Fang Ba
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Yushi Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Wan-Qiu Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Xintong Tian
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Jian Li
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
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52
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Qiu X, Zhang Y, Martin-Rufino JD, Weng C, Hosseinzadeh S, Yang D, Pogson AN, Hein MY, Hoi Joseph Min K, Wang L, Grody EI, Shurtleff MJ, Yuan R, Xu S, Ma Y, Replogle JM, Lander ES, Darmanis S, Bahar I, Sankaran VG, Xing J, Weissman JS. Mapping transcriptomic vector fields of single cells. Cell 2022; 185:690-711.e45. [PMID: 35108499 PMCID: PMC9332140 DOI: 10.1016/j.cell.2021.12.045] [Citation(s) in RCA: 144] [Impact Index Per Article: 72.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 10/08/2021] [Accepted: 12/28/2021] [Indexed: 01/03/2023]
Abstract
Single-cell (sc)-RNA-seq, together with RNA-velocity and metabolic labeling, reveals cellular states and transitions at unprecedented resolution. Fully exploiting these data, however, requires kinetic models capable of unveiling governing regulatory functions. Here, we introduce an analytical framework dynamo, that infers absolute RNA velocity, reconstructs continuous vector-field functions that predict cell fates, employs differential geometry to extract underlying regulations, and ultimately predicts optimal reprogramming paths and perturbation outcomes. We highlight dynamo’s power to overcome fundamental limitations of conventional splicing-based RNA velocity analyses to enable accurate velocity estimations on a metabolically-labeled human hematopoiesis scRNA-seq dataset. Furthermore, differential geometry analyses reveal mechanisms driving early megakaryocyte appearance and elucidate asymmetrical regulation within the PU.1–GATA1 circuit. Leveraging the Least-Action-Path method, dynamo accurately predicts drivers of numerous hematopoietic transitions. Finally, in silico perturbations predict cell-fate diversions induced by gene perturbations. Dynamo thus represents an important step in advancing quantitative and predictive theories of cell-state transitions.
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Affiliation(s)
- Xiaojie Qiu
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Yan Zhang
- Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, PA, USA; Joint CMU-Pitt Ph.D. Program in Computational Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Jorge D Martin-Rufino
- Broad Institute of MIT and Harvard, Cambridge, MA, USA; Division of Hematology/Oncology, Boston Children's Hospital and Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
| | - Chen Weng
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA; Division of Hematology/Oncology, Boston Children's Hospital and Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
| | - Shayan Hosseinzadeh
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
| | - Dian Yang
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Angela N Pogson
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Marco Y Hein
- Chan Zuckerberg Biohub, 499 Illinois St, San Francisco, CA 94158, USA
| | - Kyung Hoi Joseph Min
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA; Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Li Wang
- Department of Mathematics, University of Texas at Arlington, Arlington, TX, USA
| | | | | | - Ruoshi Yuan
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA, USA
| | | | - Yian Ma
- Halıcıoğlu Data Science Institute, University of California San Diego, San Diego, CA, USA
| | - Joseph M Replogle
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA; Medical Scientist Training Program, University of California, San Francisco, CA, USA
| | - Eric S Lander
- Broad Institute of MIT and Harvard, Cambridge, MA, USA; Department of Systems Biology Harvard Medical School, Boston, MA 02125, USA; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | | | - Ivet Bahar
- Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, PA, USA; Joint CMU-Pitt Ph.D. Program in Computational Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Vijay G Sankaran
- Broad Institute of MIT and Harvard, Cambridge, MA, USA; Division of Hematology/Oncology, Boston Children's Hospital and Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
| | - Jianhua Xing
- Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, PA, USA; Joint CMU-Pitt Ph.D. Program in Computational Biology, University of Pittsburgh, Pittsburgh, PA, USA; UPMC-Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA, USA; Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA.
| | - Jonathan S Weissman
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA; Koch Institute For Integrative Cancer Research at MIT, MIT, Cambridge, MA, USA.
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53
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Ronda C, Wang HH. Engineering temporal dynamics in microbial communities. Curr Opin Microbiol 2022; 65:47-55. [PMID: 34739926 PMCID: PMC10659046 DOI: 10.1016/j.mib.2021.10.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Revised: 09/05/2021] [Accepted: 10/08/2021] [Indexed: 12/20/2022]
Abstract
Microbial communities are a key part to tackling global challenges in human health, environmental conservation, and sustainable agriculture in the coming decade. Recent advances in synthetic biology to study and modify microbial communities have led to important insights into their physiology and ecology. Understanding how targeted changes to microbial communities result in reproducible alterations of the community's intrinsic fluctuations and function is important for mechanistic reconstruction of microbiomes. Studies of synthetic microbial consortia and comparative analysis of communities in normal and disrupted states have revealed ecological principles that can be leveraged to engineer communities towards desired functions. Tools enabling temporal modulation and sensing of the community dynamics offer precise spatiotemporal control of functions, help to dissect microbial interaction networks, and improve predictions of population temporal dynamics. Here we discuss recent advances to manipulate microbiome dynamics through control of specific strain engraftment and abundance, modulation of cell-cell signaling for tuning population dynamics, infiltration of new functions in the existing community with in situ engineering, and in silico modeling of microbial consortia to predict community function and ecology.
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Affiliation(s)
- Carlotta Ronda
- Department of Systems Biology, Columbia University, New York, NY, USA
| | - Harris H Wang
- Department of Systems Biology, Columbia University, New York, NY, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY, USA.
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54
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Jiao C, Beisel CL. Reprogramming TracrRNAs for Multiplexed RNA Detection. Methods Mol Biol 2022; 2518:217-235. [PMID: 35666448 DOI: 10.1007/978-1-0716-2421-0_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
CRISPR-based detection and recording technologies are gaining increasing attention in disease surveillance and prevention. In this chapter, we describe how our recent discovery of noncanonical crRNAs inspired the engineering of reprogrammed tracrRNAs and led to a powerful platform for multiplexed RNA detection. We provide detailed protocols regarding how to design reprogrammed tracrRNA and carry out assays in vitro and in vivo.
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Affiliation(s)
- Chunlei Jiao
- Helmholtz Institute for RNA-based Infection Research (HIRI), Helmholtz-Centre for Infection Research (HZI), Würzburg, Germany
| | - Chase L Beisel
- Helmholtz Institute for RNA-based Infection Research (HIRI), Helmholtz-Centre for Infection Research (HZI), Würzburg, Germany.
- Medical Faculty, University of Würzburg, Würzburg, Germany.
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55
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Kok L, Masopust D, Schumacher TN. The precursors of CD8 + tissue resident memory T cells: from lymphoid organs to infected tissues. Nat Rev Immunol 2022; 22:283-293. [PMID: 34480118 PMCID: PMC8415193 DOI: 10.1038/s41577-021-00590-3] [Citation(s) in RCA: 85] [Impact Index Per Article: 42.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/05/2021] [Indexed: 02/08/2023]
Abstract
CD8+ tissue resident memory T cells (TRM cells) are essential for immune defence against pathogens and malignancies, and the molecular processes that lead to TRM cell formation are therefore of substantial biomedical interest. Prior work has demonstrated that signals present in the inflamed tissue micro-environment can promote the differentiation of memory precursor cells into mature TRM cells, and it was therefore long assumed that TRM cell formation adheres to a 'local divergence' model, in which TRM cell lineage decisions are exclusively made within the tissue. However, a growing body of work provides evidence for a 'systemic divergence' model, in which circulating T cells already become preconditioned to preferentially give rise to the TRM cell lineage, resulting in the generation of a pool of TRM cell-poised T cells within the lymphoid compartment. Here, we review the emerging evidence that supports the existence of such a population of circulating TRM cell progenitors, discuss current insights into their formation and highlight open questions in the field.
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Affiliation(s)
- Lianne Kok
- grid.430814.a0000 0001 0674 1393Division of Molecular Oncology & Immunology, Oncode Institute, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - David Masopust
- grid.17635.360000000419368657Department of Microbiology and Immunology, Center for Immunology, University of Minnesota Medical School, Minneapolis, MN USA
| | - Ton N. Schumacher
- grid.430814.a0000 0001 0674 1393Division of Molecular Oncology & Immunology, Oncode Institute, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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56
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Ibrahim AU, Al-Turjman F, Sa’id Z, Ozsoz M. Futuristic CRISPR-based biosensing in the cloud and internet of things era: an overview. MULTIMEDIA TOOLS AND APPLICATIONS 2022; 81:35143-35171. [PMID: 32837247 PMCID: PMC7276962 DOI: 10.1007/s11042-020-09010-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 03/16/2020] [Accepted: 05/01/2020] [Indexed: 05/02/2023]
Abstract
Biosensors-based devices are transforming medical diagnosis of diseases and monitoring of patient signals. The development of smart and automated molecular diagnostic tools equipped with biomedical big data analysis, cloud computing and medical artificial intelligence can be an ideal approach for the detection and monitoring of diseases, precise therapy, and storage of data over the cloud for supportive decisions. This review focused on the use of machine learning approaches for the development of futuristic CRISPR-biosensors based on microchips and the use of Internet of Things for wireless transmission of signals over the cloud for support decision making. The present review also discussed the discovery of CRISPR, its usage as a gene editing tool, and the CRISPR-based biosensors with high sensitivity of Attomolar (10-18 M), Femtomolar (10-15 M) and Picomolar (10-12 M) in comparison to conventional biosensors with sensitivity of nanomolar 10-9 M and micromolar 10-3 M. Additionally, the review also outlines limitations and open research issues in the current state of CRISPR-based biosensing applications.
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Affiliation(s)
| | - Fadi Al-Turjman
- Department of Artificial Intelligence, Near East University, Nicosia, 10 Mersin, Turkey
| | - Zubaida Sa’id
- Department of Biomedical Engineering, Near East University, Nicosia, 10 Mersin, Turkey
| | - Mehmet Ozsoz
- Department of Biomedical Engineering, Near East University, Nicosia, 10 Mersin, Turkey
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57
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Chen T, Ali Al-Radhawi M, Voigt CA, Sontag ED. A synthetic distributed genetic multi-bit counter. iScience 2021; 24:103526. [PMID: 34917900 PMCID: PMC8666654 DOI: 10.1016/j.isci.2021.103526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Revised: 09/30/2021] [Accepted: 11/23/2021] [Indexed: 11/12/2022] Open
Abstract
A design for genetically encoded counters is proposed via repressor-based circuits. An N-bit counter reads sequences of input pulses and displays the total number of pulses, modulo 2N. The design is based on distributed computation with specialized cell types allocated to specific tasks. This allows scalability and bypasses constraints on the maximal number of circuit genes per cell due to toxicity or failures due to resource limitations. The design starts with a single-bit counter. The N-bit counter is then obtained by interconnecting (using diffusible chemicals) a set of N single-bit counters and connector modules. An optimization framework is used to determine appropriate gate parameters and to compute bounds on admissible pulse widths and relaxation (inter-pulse) times, as well as to guide the construction of novel gates. This work can be viewed as a step toward obtaining circuits that are capable of finite automaton computation in analogy to digital central processing units. A single-bit counter is designed for a repressor-based genetic circuit A scalable multi-bit counter is enabled by distributing the design across cells A computational optimization framework is proposed to guide the design
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Affiliation(s)
- Tianchi Chen
- Department of Bioengineering, Northeastern University, Boston, MA 02115, USA
| | - M Ali Al-Radhawi
- Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 02115, USA
| | - Christopher A Voigt
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Eduardo D Sontag
- Department of Bioengineering, Northeastern University, Boston, MA 02115, USA.,Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 02115, USA.,Laboratory of Systems Pharmacology, Program in Therapeutic Science, Harvard Medical School, Boston, MA 02115, USA
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58
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Abstract
Nuclei are central hubs for information processing in eukaryotic cells. The need to fit large genomes into small nuclei imposes severe restrictions on genome organization and the mechanisms that drive genome-wide regulatory processes. How a disordered polymer such as chromatin, which has vast heterogeneity in its DNA and histone modification profiles, folds into discernibly consistent patterns is a fundamental question in biology. Outstanding questions include how genomes are spatially and temporally organized to regulate cellular processes with high precision and whether genome organization is causally linked to transcription regulation. The advent of next-generation sequencing, super-resolution imaging, multiplexed fluorescent in situ hybridization, and single-molecule imaging in individual living cells has caused a resurgence in efforts to understand the spatiotemporal organization of the genome. In this review, we discuss structural and mechanistic properties of genome organization at different length scales and examine changes in higher-order chromatin organization during important developmental transitions.
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Affiliation(s)
- Rajarshi P Ghosh
- Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA; ,
| | - Barbara J Meyer
- Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA; ,
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59
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A light tunable differentiation system for the creation and control of consortia in yeast. Nat Commun 2021; 12:5829. [PMID: 34611168 PMCID: PMC8492667 DOI: 10.1038/s41467-021-26129-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Accepted: 09/07/2021] [Indexed: 02/08/2023] Open
Abstract
Artificial microbial consortia seek to leverage division-of-labour to optimize function and possess immense potential for bioproduction. Co-culturing approaches, the preferred mode of generating a consortium, remain limited in their ability to give rise to stable consortia having finely tuned compositions. Here, we present an artificial differentiation system in budding yeast capable of generating stable microbial consortia with custom functionalities from a single strain at user-defined composition in space and in time based on optogenetically-driven genetic rewiring. Owing to fast, reproducible, and light-tunable dynamics, our system enables dynamic control of consortia composition in continuous cultures for extended periods. We further demonstrate that our system can be extended in a straightforward manner to give rise to consortia with multiple subpopulations. Our artificial differentiation strategy establishes a novel paradigm for the creation of complex microbial consortia that are simple to implement, precisely controllable, and versatile to use.
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60
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Konur S, Mierla L, Fellermann H, Ladroue C, Brown B, Wipat A, Twycross J, Dun BP, Kalvala S, Gheorghe M, Krasnogor N. Toward Full-Stack In Silico Synthetic Biology: Integrating Model Specification, Simulation, Verification, and Biological Compilation. ACS Synth Biol 2021; 10:1931-1945. [PMID: 34339602 DOI: 10.1021/acssynbio.1c00143] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We present the Infobiotics Workbench (IBW), a user-friendly, scalable, and integrated computational environment for the computer-aided design of synthetic biological systems. It supports an iterative workflow that begins with specification of the desired synthetic system, followed by simulation and verification of the system in high-performance environments and ending with the eventual compilation of the system specification into suitable genetic constructs. IBW integrates modeling, simulation, verification, and biocompilation features into a single software suite. This integration is achieved through a new domain-specific biological programming language, the Infobiotics Language (IBL), which tightly combines these different aspects of in silico synthetic biology into a full-stack integrated development environment. Unlike existing synthetic biology modeling or specification languages, IBL uniquely blends modeling, verification, and biocompilation statements into a single file. This allows biologists to incorporate design constraints within the specification file rather than using decoupled and independent formalisms for different in silico analyses. This novel approach offers seamless interoperability across different tools as well as compatibility with SBOL and SBML frameworks and removes the burden of doing manual translations for standalone applications. We demonstrate the features, usability, and effectiveness of IBW and IBL using well-established synthetic biological circuits.
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Affiliation(s)
- Savas Konur
- Department of Computer Science, University of Bradford, Bradford, BD7 1DP, U.K
| | - Laurentiu Mierla
- Department of Computer Science, University of Bradford, Bradford, BD7 1DP, U.K
| | - Harold Fellermann
- Interdisciplinary Computing and Complex Biosystems Research Group, Newcastle University, Newcastle, NE1 7RU, U.K
| | - Christophe Ladroue
- Department of Computer Science, University of Warwick, Coventry, CV4 7AL, U.K
| | - Bradley Brown
- Interdisciplinary Computing and Complex Biosystems Research Group, Newcastle University, Newcastle, NE1 7RU, U.K
| | - Anil Wipat
- Interdisciplinary Computing and Complex Biosystems Research Group, Newcastle University, Newcastle, NE1 7RU, U.K
| | - Jamie Twycross
- School of Computer Science, University of Nottingham, Nottingham, NG8 1BB, U.K
| | - Boyang Peter Dun
- Department of Computer Science, Stanford University, Stanford, California 94305, United States
| | - Sara Kalvala
- Department of Computer Science, University of Warwick, Coventry, CV4 7AL, U.K
| | - Marian Gheorghe
- Department of Computer Science, University of Bradford, Bradford, BD7 1DP, U.K
| | - Natalio Krasnogor
- Interdisciplinary Computing and Complex Biosystems Research Group, Newcastle University, Newcastle, NE1 7RU, U.K
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61
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A last-in first-out stack data structure implemented in DNA. Nat Commun 2021; 12:4861. [PMID: 34381035 PMCID: PMC8358042 DOI: 10.1038/s41467-021-25023-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 07/08/2021] [Indexed: 11/25/2022] Open
Abstract
DNA-based memory systems are being reported with increasing frequency. However, dynamic DNA data structures able to store and recall information in an ordered way, and able to be interfaced with external nucleic acid computing circuits, have so far received little attention. Here we present an in vitro implementation of a stack data structure using DNA polymers. The stack is able to record combinations of two different DNA signals, release the signals into solution in reverse order, and then re-record. We explore the accuracy limits of the stack data structure through a stochastic rule-based model of the underlying polymerisation chemistry. We derive how the performance of the stack increases with the efficiency of washing steps between successive reaction stages, and report how stack performance depends on the history of stack operations under inefficient washing. Finally, we discuss refinements to improve molecular synchronisation and future open problems in implementing an autonomous chemical data structure. DNA is becoming increasingly used as a medium to store non-genetic information. Here the authors present a dynamic stack data structure implemented as a DNA polymer chemistry able to record and retrieve signals in a last-in first-out order.
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62
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Gangadharan S, Raman K. The art of molecular computing: Whence and whither. Bioessays 2021; 43:e2100051. [PMID: 34101866 DOI: 10.1002/bies.202100051] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 05/11/2021] [Accepted: 05/18/2021] [Indexed: 12/30/2022]
Abstract
An astonishingly diverse biomolecular circuitry orchestrates the functioning machinery underlying every living cell. These biomolecules and their circuits have been engineered not only for various industrial applications but also to perform other atypical functions that they were not evolved for-including computation. Various kinds of computational challenges, such as solving NP-complete problems with many variables, logical computation, neural network operations, and cryptography, have all been attempted through this unconventional computing paradigm. In this review, we highlight key experiments across three different ''eras'' of molecular computation, beginning with molecular solutions, transitioning to logic circuits and ultimately, more complex molecular networks. We also discuss a variety of applications of molecular computation, from solving NP-hard problems to self-assembled nanostructures for delivering molecules, and provide a glimpse into the exciting potential that molecular computing holds for the future. Also see the video abstract here: https://youtu.be/9Mw0K0vCSQw.
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Affiliation(s)
- Sahana Gangadharan
- Bhupat and Jyoti Mehta School of Biosciences, Department of Biotechnology, Indian Institute of Technology Madras, Chennai, India.,Initiative for Biological Systems Engineering, Indian Institute of Technology Madras, Chennai, India
| | - Karthik Raman
- Bhupat and Jyoti Mehta School of Biosciences, Department of Biotechnology, Indian Institute of Technology Madras, Chennai, India.,Initiative for Biological Systems Engineering, Indian Institute of Technology Madras, Chennai, India.,Robert Bosch Centre for Data Science and Artificial Intelligence (RBCDSAI), Indian Institute of Technology Madras, Chennai, India
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63
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Xu C, Zhao C, Ma B, Liu H. Uncertainties in synthetic DNA-based data storage. Nucleic Acids Res 2021; 49:5451-5469. [PMID: 33836076 PMCID: PMC8191772 DOI: 10.1093/nar/gkab230] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 02/16/2021] [Accepted: 03/22/2021] [Indexed: 12/12/2022] Open
Abstract
Deoxyribonucleic acid (DNA) has evolved to be a naturally selected, robust biomacromolecule for gene information storage, and biological evolution and various diseases can find their origin in uncertainties in DNA-related processes (e.g. replication and expression). Recently, synthetic DNA has emerged as a compelling molecular media for digital data storage, and it is superior to the conventional electronic memory devices in theoretical retention time, power consumption, storage density, and so forth. However, uncertainties in the in vitro DNA synthesis and sequencing, along with its conjugation chemistry and preservation conditions can lead to severe errors and data loss, which limit its practical application. To maintain data integrity, complicated error correction algorithms and substantial data redundancy are usually required, which can significantly limit the efficiency and scale-up of the technology. Herein, we summarize the general procedures of the state-of-the-art DNA-based digital data storage methods (e.g. write, read, and preservation), highlighting the uncertainties involved in each step as well as potential approaches to correct them. We also discuss challenges yet to overcome and research trends in the promising field of DNA-based data storage.
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Affiliation(s)
- Chengtao Xu
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Chao Zhao
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Biao Ma
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Hong Liu
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, Jiangsu 210096, China
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64
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Loveless TB, Grotts JH, Schechter MW, Forouzmand E, Carlson CK, Agahi BS, Liang G, Ficht M, Liu B, Xie X, Liu CC. Lineage tracing and analog recording in mammalian cells by single-site DNA writing. Nat Chem Biol 2021; 17:739-747. [PMID: 33753928 PMCID: PMC8891441 DOI: 10.1038/s41589-021-00769-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 02/09/2021] [Indexed: 01/31/2023]
Abstract
Studying cellular and developmental processes in complex multicellular organisms can require the non-destructive observation of thousands to billions of cells deep within an animal. DNA recorders address the staggering difficulty of this task by converting transient cellular experiences into mutations at defined genomic sites that can be sequenced later in high throughput. However, existing recorders act primarily by erasing DNA. This is problematic because, in the limit of progressive erasure, no record remains. We present a DNA recorder called CHYRON (Cell History Recording by Ordered Insertion) that acts primarily by writing new DNA through the repeated insertion of random nucleotides at a single locus in temporal order. To achieve in vivo DNA writing, CHYRON combines Cas9, a homing guide RNA and the template-independent DNA polymerase terminal deoxynucleotidyl transferase. We successfully applied CHYRON as an evolving lineage tracer and as a recorder of user-selected cellular stimuli.
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Affiliation(s)
- Theresa B Loveless
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
- NSF-Simons Center for Multiscale Cell Fate Research, University of California, Irvine, Irvine, CA, USA
| | - Joseph H Grotts
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Mason W Schechter
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Elmira Forouzmand
- Department of Computer Science, University of California, Irvine, Irvine, CA, USA
| | - Courtney K Carlson
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Bijan S Agahi
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Guohao Liang
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Michelle Ficht
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Beide Liu
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Xiaohui Xie
- Department of Computer Science, University of California, Irvine, Irvine, CA, USA
| | - Chang C Liu
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, USA.
- NSF-Simons Center for Multiscale Cell Fate Research, University of California, Irvine, Irvine, CA, USA.
- Department of Chemistry, University of California, Irvine, Irvine, CA, USA.
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, USA.
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, USA.
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65
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Chow KHK, Budde MW, Granados AA, Cabrera M, Yoon S, Cho S, Huang TH, Koulena N, Frieda KL, Cai L, Lois C, Elowitz MB. Imaging cell lineage with a synthetic digital recording system. Science 2021; 372:eabb3099. [PMID: 33833095 DOI: 10.1126/science.abb3099] [Citation(s) in RCA: 59] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 02/25/2021] [Indexed: 12/13/2022]
Abstract
During multicellular development, spatial position and lineage history play powerful roles in controlling cell fate decisions. Using a serine integrase-based recording system, we engineered cells to record lineage information in a format that can be read out in situ. The system, termed integrase-editable memory by engineered mutagenesis with optical in situ readout (intMEMOIR), allowed in situ reconstruction of lineage relationships in cultured mouse cells and flies. intMEMOIR uses an array of independent three-state genetic memory elements that can recombine stochastically and irreversibly, allowing up to 59,049 distinct digital states. It reconstructed lineage trees in stem cells and enabled simultaneous analysis of single-cell clonal history, spatial position, and gene expression in Drosophila brain sections. These results establish a foundation for microscopy-readable lineage recording and analysis in diverse systems.
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Affiliation(s)
- Ke-Huan K Chow
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Mark W Budde
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Alejandro A Granados
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Maria Cabrera
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Shinae Yoon
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Soomin Cho
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Ting-Hao Huang
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Noushin Koulena
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | | | - Long Cai
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Carlos Lois
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
| | - Michael B Elowitz
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
- Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA
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66
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Tang TC, Tham E, Liu X, Yehl K, Rovner AJ, Yuk H, de la Fuente-Nunez C, Isaacs FJ, Zhao X, Lu TK. Hydrogel-based biocontainment of bacteria for continuous sensing and computation. Nat Chem Biol 2021; 17:724-731. [PMID: 33820990 DOI: 10.1038/s41589-021-00779-6] [Citation(s) in RCA: 82] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Accepted: 02/25/2021] [Indexed: 12/12/2022]
Abstract
Genetically modified microorganisms (GMMs) can enable a wide range of important applications including environmental sensing and responsive engineered living materials. However, containment of GMMs to prevent environmental escape and satisfy regulatory requirements is a bottleneck for real-world use. While current biochemical strategies restrict unwanted growth of GMMs in the environment, there is a need for deployable physical containment technologies to achieve redundant, multi-layered and robust containment. We developed a hydrogel-based encapsulation system that incorporates a biocompatible multilayer tough shell and an alginate-based core. This deployable physical containment strategy (DEPCOS) allows no detectable GMM escape, bacteria to be protected against environmental insults including antibiotics and low pH, controllable lifespan and easy retrieval of genomically recoded bacteria. To highlight the versatility of DEPCOS, we demonstrated that robustly encapsulated cells can execute useful functions, including performing cell-cell communication with other encapsulated bacteria and sensing heavy metals in water samples from the Charles River.
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Affiliation(s)
- Tzu-Chieh Tang
- Synthetic Biology Group, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA. .,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA. .,The Mediated Matter Group, Media Laboratory, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Eléonore Tham
- Synthetic Biology Group, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA.,Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Xinyue Liu
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kevin Yehl
- Synthetic Biology Group, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA.,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.,Department of Chemistry and Biochemistry, Miami University, Oxford, OH, USA
| | - Alexis J Rovner
- Wyss Institute for Biologically Inspired Engineering, Boston, MA, USA.,Department of Genetics, Harvard Medical School, Harvard University, Boston, MA, USA
| | - Hyunwoo Yuk
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Cesar de la Fuente-Nunez
- Machine Biology Group, Departments of Psychiatry and Microbiology, Institute for Biomedical Informatics, Institute for Translational Medicine and Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.,Departments of Bioengineering and Chemical and Biomolecular Engineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA, USA.,Penn Institute for Computational Science, University of Pennsylvania, Philadelphia, PA, USA
| | - Farren J Isaacs
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT, USA.,Systems Biology Institute, Yale University, West Haven, CT, USA.,Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Xuanhe Zhao
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA. .,Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Timothy K Lu
- Synthetic Biology Group, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA. .,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA. .,Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA.
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67
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Yim SS, McBee RM, Song AM, Huang Y, Sheth RU, Wang HH. Robust direct digital-to-biological data storage in living cells. Nat Chem Biol 2021; 17:246-253. [PMID: 33432236 PMCID: PMC7904632 DOI: 10.1038/s41589-020-00711-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 10/30/2020] [Accepted: 11/12/2020] [Indexed: 02/06/2023]
Abstract
DNA has been the predominant information storage medium for biology and holds great promise as a next-generation high-density data medium in the digital era. Currently, the vast majority of DNA-based data storage approaches rely on in vitro DNA synthesis. As such, there are limited methods to encode digital data into the chromosomes of living cells in a single step. Here, we describe a new electrogenetic framework for direct storage of digital data in living cells. Using an engineered redox-responsive CRISPR adaptation system, we encoded binary data in 3-bit units into CRISPR arrays of bacterial cells by electrical stimulation. We demonstrate multiplex data encoding into barcoded cell populations to yield meaningful information storage and capacity up to 72 bits, which can be maintained over many generations in natural open environments. This work establishes a direct digital-to-biological data storage framework and advances our capacity for information exchange between silicon- and carbon-based entities.
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Affiliation(s)
- Sung Sun Yim
- Department of Systems Biology, Columbia University, New York, NY, USA
| | - Ross M McBee
- Department of Systems Biology, Columbia University, New York, NY, USA
- Department of Biological Sciences, Columbia University, New York, NY, USA
| | - Alan M Song
- Department of Systems Biology, Columbia University, New York, NY, USA
| | - Yiming Huang
- Department of Systems Biology, Columbia University, New York, NY, USA
- Integrated Program in Cellular, Molecular, and Biomedical Studies, Columbia University, New York, NY, USA
| | - Ravi U Sheth
- Department of Systems Biology, Columbia University, New York, NY, USA
- Integrated Program in Cellular, Molecular, and Biomedical Studies, Columbia University, New York, NY, USA
| | - Harris H Wang
- Department of Systems Biology, Columbia University, New York, NY, USA.
- Department of Pathology and Cell Biology, Columbia University, New York, NY, USA.
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68
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Del Valle I, Fulk EM, Kalvapalle P, Silberg JJ, Masiello CA, Stadler LB. Translating New Synthetic Biology Advances for Biosensing Into the Earth and Environmental Sciences. Front Microbiol 2021; 11:618373. [PMID: 33633695 PMCID: PMC7901896 DOI: 10.3389/fmicb.2020.618373] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 12/17/2020] [Indexed: 12/26/2022] Open
Abstract
The rapid diversification of synthetic biology tools holds promise in making some classically hard-to-solve environmental problems tractable. Here we review longstanding problems in the Earth and environmental sciences that could be addressed using engineered microbes as micron-scale sensors (biosensors). Biosensors can offer new perspectives on open questions, including understanding microbial behaviors in heterogeneous matrices like soils, sediments, and wastewater systems, tracking cryptic element cycling in the Earth system, and establishing the dynamics of microbe-microbe, microbe-plant, and microbe-material interactions. Before these new tools can reach their potential, however, a suite of biological parts and microbial chassis appropriate for environmental conditions must be developed by the synthetic biology community. This includes diversifying sensing modules to obtain information relevant to environmental questions, creating output signals that allow dynamic reporting from hard-to-image environmental materials, and tuning these sensors so that they reliably function long enough to be useful for environmental studies. Finally, ethical questions related to the use of synthetic biosensors in environmental applications are discussed.
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Affiliation(s)
- Ilenne Del Valle
- Systems, Synthetic, and Physical Biology Graduate Program, Rice University, Houston, TX, United States
| | - Emily M. Fulk
- Systems, Synthetic, and Physical Biology Graduate Program, Rice University, Houston, TX, United States
| | - Prashant Kalvapalle
- Systems, Synthetic, and Physical Biology Graduate Program, Rice University, Houston, TX, United States
| | - Jonathan J. Silberg
- Department of BioSciences, Rice University, Houston, TX, United States
- Department of Bioengineering, Rice University, Houston, TX, United States
- Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX, United States
| | - Caroline A. Masiello
- Department of BioSciences, Rice University, Houston, TX, United States
- Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX, United States
- Department of Chemistry, Rice University, Houston, TX, United States
| | - Lauren B. Stadler
- Department of Civil and Environmental Engineering, Rice University, Houston, TX, United States
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69
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Lim CK, Nirantar S, Yew WS, Poh CL. Novel Modalities in DNA Data Storage. Trends Biotechnol 2021; 39:990-1003. [PMID: 33455842 DOI: 10.1016/j.tibtech.2020.12.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2020] [Revised: 12/14/2020] [Accepted: 12/15/2020] [Indexed: 10/22/2022]
Abstract
The field of storing information in DNA has expanded exponentially. Most common modalities involve encoding information from bits into synthesized nucleotides, storage in liquid or dry media, and decoding via sequencing. However, limitations to this paradigm include the cost of DNA synthesis and sequencing, along with low throughput. Further unresolved questions include the appropriate media of storage and the scalability of such approaches for commercial viability. In this review, we examine various storage modalities involving the use of DNA from a systems-level perspective. We compare novel methods that draw inspiration from molecular biology techniques that have been devised to overcome the difficulties posed by standard workflows and conceptualize potential applications that can arise from these advances.
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Affiliation(s)
- Cheng Kai Lim
- NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore, Singapore 119077, Singapore; NUS Synthetic Biology for Clinical and Technological Innovation (SynCTI), Centre for Life Sciences, National University of Singapore, Singapore 117456, Singapore
| | | | - Wen Shan Yew
- Department of Biochemistry, Faculty of Medicine, National University of Singapore, Singapore 117597, Singapore; NUS Synthetic Biology for Clinical and Technological Innovation (SynCTI), Centre for Life Sciences, National University of Singapore, Singapore 117456, Singapore
| | - Chueh Loo Poh
- Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore 117583, Singapore; NUS Synthetic Biology for Clinical and Technological Innovation (SynCTI), Centre for Life Sciences, National University of Singapore, Singapore 117456, Singapore.
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70
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Al Khabouri S, Gerlach C. T cell fate mapping and lineage tracing technologies probing clonal aspects underlying the generation of CD8 T cell subsets. Scand J Immunol 2020; 92:e12983. [PMID: 33037653 PMCID: PMC7757170 DOI: 10.1111/sji.12983] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Revised: 10/02/2020] [Accepted: 10/05/2020] [Indexed: 12/18/2022]
Abstract
T cells responding to acute infections generally provide two key functions to protect the host: (1) active contribution to pathogen elimination and (2) providing long‐lived cells that are poised to rapidly respond to renewed infection, thus ensuring long‐lasting protection against the particular pathogen. Extensive work has established an astonishing amount of additional diversity among T cells actively contributing to pathogen elimination, as well as among resting, long‐lived antigen‐experienced T cells. This led to the description of a variety of functionally distinct T cell ‘subsets’. Understanding how this heterogeneity develops among T cells responding to the same antigen is currently an active area of research, since knowledge of such mechanisms may have implications for the development of vaccines and immunotherapy. The number of naïve T cells specific to a given antigen span a great range. Considering this, one mechanistic angle focusses on how individual naïve T cells contribute to the development of the distinct T cell subsets. In this review, we highlight the current technologies that enable one to address the contributions of individual naïve T cells to different T cell subsets, with a focus on CD8 T cell subsets generated in the context of acute infections. Moreover, we discuss the requirements of new technologies to further our understanding of the mechanisms that help generate long‐lasting immunity.
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Affiliation(s)
- Shaima Al Khabouri
- Division of Rheumatology, Department of Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.,Center for Molecular Medicine, Karolinska University Hospital Solna, Stockholm, Sweden
| | - Carmen Gerlach
- Division of Rheumatology, Department of Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.,Center for Molecular Medicine, Karolinska University Hospital Solna, Stockholm, Sweden
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71
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Zou ZP, Ye BC. Long-Term Rewritable Report and Recording of Environmental Stimuli in Engineered Bacterial Populations. ACS Synth Biol 2020; 9:2440-2449. [PMID: 32794765 DOI: 10.1021/acssynbio.0c00193] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
DNA writing (living sensing recorders) based whole-cell biosensors can capture transient signals and then convert them into readable genomic DNA changes. The primitive signals can be easily obtained by sequencing technology or analysis of protein activity (such as fluorescent protein). However, the functions of the current living sensing recorders still need to be expanded, and the difficulty of rewriting in complex biological environments has further limited their applications. In this study, we designed a long-term rewritable recording system using a CRISPR base editor-based synthetic genetic circuit, named CRISPR-istop. This system can convert stimuli into changes in the fluorescence intensity (reporter) and single-base mutations in genomic DNA (recording). Furthermore, we updated the biological circuit through the strategy of coupling the single-base mutation (record site) and the loss-of-function of the targeted protein (translation stopped by stop codon introduction), and we can remove edited bacteria from a population through selective sweeps upon applying a selective pressure. It successfully conducted the rewritable reporter and recording of the nutrient arabinose and pollutant arsenite with two rounds of continuous operation (10 passages/round, 12 h/passage). These observations indicated that the CRISPR-istop system can report and record stimuli over time; moreover, the recording can be manually erased and rewritten as needed. This method has great potential to be extended to more complicated recording systems to execute sophisticated tasks in inaccessible environments for synthetic biology and biomedical applications, such as monitoring disease-relevant physiological markers or other molecules.
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Affiliation(s)
- Zhen-Ping Zou
- Laboratory of Biosystems and Microanalysis, Institute of Engineering Biology and Health, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai 200237, China
| | - Bang-Ce Ye
- Laboratory of Biosystems and Microanalysis, Institute of Engineering Biology and Health, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai 200237, China
- Institute of Engineering Biology and Health, Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, Zhejiang, China
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72
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73
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Tanna T, Ramachanderan R, Platt RJ. Engineered bacteria to report gut function: technologies and implementation. Curr Opin Microbiol 2020; 59:24-33. [PMID: 32828048 DOI: 10.1016/j.mib.2020.07.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 07/22/2020] [Accepted: 07/26/2020] [Indexed: 12/15/2022]
Abstract
Advances in synthetic biology and microbiology have enabled the creation of engineered bacteria which can sense and report on intracellular and extracellular signals. When deployed in vivo these whole-cell bacterial biosensors can act as sentinels to monitor biomolecules of interest in human health and disease settings. This is particularly interesting in the context of the gut microbiota, which interacts extensively with the human host throughout time and transit of the gut and can be accessed from feces without requiring invasive collection. Leveraging rational engineering approaches for genetic circuits as well as an expanding catalog of disease-associated biomarkers, bacterial biosensors can act as non-invasive and easy-to-monitor reporters of the gut. Here, we summarize recent engineering approaches applied in vivo in animal models and then highlight promising technologies for designing the next generation of bacterial biosensors.
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Affiliation(s)
- Tanmay Tanna
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, 4058 Basel, Switzerland; Department of Computer Science, ETH Zurich, Universitätstrasse 6, 8092 Zürich, Switzerland
| | - Raghavendra Ramachanderan
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, 4058 Basel, Switzerland
| | - Randall J Platt
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, 4058 Basel, Switzerland; Department of Chemistry, University of Basel, Petersplatz 1, 4003 Basel, Switzerland; Botnar Research Centre for Child Health, Basel, Switzerland.
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74
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Pradhan S, Brooks A, Yadavalli V. Nature-derived materials for the fabrication of functional biodevices. Mater Today Bio 2020; 7:100065. [PMID: 32613186 PMCID: PMC7317235 DOI: 10.1016/j.mtbio.2020.100065] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 06/04/2020] [Accepted: 06/08/2020] [Indexed: 11/18/2022] Open
Abstract
Nature provides an incredible source of inspiration, structural concepts, and materials toward applications to improve the lives of people around the world, while preserving ecosystems, and addressing environmental sustainability. In particular, materials derived from animal and plant sources can provide low-cost, renewable building blocks for such applications. Nature-derived materials are of interest for their properties of biodegradability, bioconformability, biorecognition, self-repair, and stimuli response. While long used in tissue engineering and regenerative medicine, their use in functional devices such as (bio)electronics, sensors, and optical systems for healthcare and biomonitoring is finding increasing attention. The objective of this review is to cover the varied nature derived and sourced materials currently used in active biodevices and components that possess electrical or electronic behavior. We discuss materials ranging from proteins and polypeptides such as silk and collagen, polysaccharides including chitin and cellulose, to seaweed derived biomaterials, and DNA. These materials may be used as passive substrates or support architectures and often, as the functional elements either by themselves or as biocomposites. We further discuss natural pigments such as melanin and indigo that serve as active elements in devices. Increasingly, combinations of different biomaterials are being used to address the challenges of fabrication and performance in human monitoring or medicine. Finally, this review gives perspectives on the sourcing, processing, degradation, and biocompatibility of these materials. This rapidly growing multidisciplinary area of research will be advanced by a systematic understanding of nature-inspired materials and design concepts in (bio)electronic devices.
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Affiliation(s)
- S. Pradhan
- Department of Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, VA, 23284, USA
| | - A.K. Brooks
- Department of Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, VA, 23284, USA
| | - V.K. Yadavalli
- Department of Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, VA, 23284, USA
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75
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Bernabé-Orts JM, Quijano-Rubio A, Vazquez-Vilar M, Mancheño-Bonillo J, Moles-Casas V, Selma S, Gianoglio S, Granell A, Orzaez D. A memory switch for plant synthetic biology based on the phage ϕC31 integration system. Nucleic Acids Res 2020; 48:3379-3394. [PMID: 32083668 PMCID: PMC7102980 DOI: 10.1093/nar/gkaa104] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 02/07/2020] [Accepted: 02/10/2020] [Indexed: 02/07/2023] Open
Abstract
Synthetic biology has advanced from the setup of basic genetic devices to the design of increasingly complex gene circuits to provide organisms with new functions. While many bacterial, fungal and mammalian unicellular chassis have been extensively engineered, this progress has been delayed in plants due to the lack of reliable DNA parts and devices that enable precise control over these new synthetic functions. In particular, memory switches based on DNA site-specific recombination have been the tool of choice to build long-term and stable synthetic memory in other organisms, because they enable a shift between two alternative states registering the information at the DNA level. Here we report a memory switch for whole plants based on the bacteriophage ϕC31 site-specific integrase. The switch was built as a modular device made of standard DNA parts, designed to control the transcriptional state (on or off) of two genes of interest by alternative inversion of a central DNA regulatory element. The state of the switch can be externally operated by action of the ϕC31 integrase (Int), and its recombination directionality factor (RDF). The kinetics, memory, and reversibility of the switch were extensively characterized in Nicotiana benthamiana plants.
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Affiliation(s)
- Joan Miquel Bernabé-Orts
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Alfredo Quijano-Rubio
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Marta Vazquez-Vilar
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Javier Mancheño-Bonillo
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Victor Moles-Casas
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Sara Selma
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Silvia Gianoglio
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Antonio Granell
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
| | - Diego Orzaez
- Instituto de Biología Molecular y Celular de Plantas (IBMCP). CSIC - Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, Spain
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76
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McCarty NS, Graham AE, Studená L, Ledesma-Amaro R. Multiplexed CRISPR technologies for gene editing and transcriptional regulation. Nat Commun 2020; 11:1281. [PMID: 32152313 PMCID: PMC7062760 DOI: 10.1038/s41467-020-15053-x] [Citation(s) in RCA: 241] [Impact Index Per Article: 60.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Accepted: 02/17/2020] [Indexed: 12/18/2022] Open
Abstract
Multiplexed CRISPR technologies, in which numerous gRNAs or Cas enzymes are expressed at once, have facilitated powerful biological engineering applications, vastly enhancing the scope and efficiencies of genetic editing and transcriptional regulation. In this review, we discuss multiplexed CRISPR technologies and describe methods for the assembly, expression and processing of synthetic guide RNA arrays in vivo. Applications that benefit from multiplexed CRISPR technologies, including cellular recorders, genetic circuits, biosensors, combinatorial genetic perturbations, large-scale genome engineering and the rewiring of metabolic pathways, are highlighted. We also offer a glimpse of emerging challenges and emphasize experimental considerations for future studies.
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Affiliation(s)
- Nicholas S McCarty
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Alicia E Graham
- Department of Bioengineering and Imperial College Centre for Synthetic Biology, Imperial College London, London, UK
| | - Lucie Studená
- Department of Bioengineering and Imperial College Centre for Synthetic Biology, Imperial College London, London, UK
| | - Rodrigo Ledesma-Amaro
- Department of Bioengineering and Imperial College Centre for Synthetic Biology, Imperial College London, London, UK.
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77
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Selective loading and processing of prespacers for precise CRISPR adaptation. Nature 2020; 579:141-145. [PMID: 32076262 DOI: 10.1038/s41586-020-2018-1] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 12/19/2019] [Indexed: 01/08/2023]
Abstract
CRISPR-Cas immunity protects prokaryotes against invading genetic elements1. It uses the highly conserved Cas1-Cas2 complex to establish inheritable memory (spacers)2-5. How Cas1-Cas2 acquires spacers from foreign DNA fragments (prespacers) and integrates them into the CRISPR locus in the correct orientation is unclear6,7. Here, using the high spatiotemporal resolution of single-molecule fluorescence, we show that Cas1-Cas2 selects precursors of prespacers from DNA in various forms-including single-stranded DNA and partial duplexes-in a manner that depends on both the length of the DNA strand and the presence of a protospacer adjacent motif (PAM) sequence. We also identify DnaQ exonucleases as enzymes that process the Cas1-Cas2-loaded prespacer precursors into mature prespacers of a suitable size for integration. Cas1-Cas2 protects the PAM sequence from maturation, which results in the production of asymmetrically trimmed prespacers and the subsequent integration of spacers in the correct orientation. Our results demonstrate the kinetic coordination of prespacer precursor selection and PAM trimming, providing insight into the mechanisms that underlie the integration of functional spacers in the CRISPR loci.
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Dong Y, Sun F, Ping Z, Ouyang Q, Qian L. DNA storage: research landscape and future prospects. Natl Sci Rev 2020; 7:1092-1107. [PMID: 34692128 PMCID: PMC8288837 DOI: 10.1093/nsr/nwaa007] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Revised: 01/06/2020] [Accepted: 01/18/2020] [Indexed: 02/06/2023] Open
Abstract
Abstract
The global demand for data storage is currently outpacing the world's storage capabilities. DNA, the carrier of natural genetic information, offers a stable, resource- and energy-efficient and sustainable data storage solution. In this review, we summarize the fundamental theory, research history, and technical challenges of DNA storage. From a quantitative perspective, we evaluate the prospect of DNA, and organic polymers in general, as a novel class of data storage medium.
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Affiliation(s)
- Yiming Dong
- Center for Quantitative Biology and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
| | - Fajia Sun
- Center for Quantitative Biology and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
| | - Zhi Ping
- Academician Workstation of BGI Synthetic Genomics, BGI-Shenzhen, Shenzhen 518083, China
| | - Qi Ouyang
- Center for Quantitative Biology and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
- The State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Long Qian
- Center for Quantitative Biology and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
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79
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Higashikuni Y, Lu TK. Advancing CRISPR-Based Programmable Platforms beyond Genome Editing in Mammalian Cells. ACS Synth Biol 2019; 8:2607-2619. [PMID: 31751114 DOI: 10.1021/acssynbio.9b00297] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Human diseases are caused by dysregulation of cellular biological programs that are encoded in DNA. Unveiling the endogenous programs and encoding new programs into the genome are key to creating novel diagnostic and therapeutic strategies. CRISPR/Cas9, originally identified in bacteria, has revolutionized genome editing in mammalian cells. Recent advances in CRISPR technologies have provided new programmable platforms for modifying cell function and behavior. CRISPR-based transcriptional regulators and modified gRNAs have enabled multiplexed regulation and visualization of genome dynamics with spatiotemporal precision. Using these toolkits, genome-scale screening platforms can identify key genetic elements or combinations thereof that modulate phenotypes in mammalian cells. In addition, imaging platforms for multiplexed genomic labeling have been created to study the conformation and dynamics of chromatin in living cells, which are essential for genome function. Furthermore, CRISPR-based computation and memory platforms have been built in living mammalian cells by using DNA as a data processing and storage medium to regulate and monitor cellular behaviors. The conditional regulation of CRISPR-based parts has enabled the design of complex multilayered biological programs. CRISPR-based memory platforms can continuously record biological events as mutations in defined DNA loci. By making use of base editors, CRISPR-based computation and memory platforms have been interconnected to perform logic operations based on past events. These technologies open up new avenues for understanding biological phenomena and designing mammalian cells as living machines for biomedical applications.
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80
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Abstract
Molecular data storage is an attractive alternative for dense and durable information storage, which is sorely needed to deal with the growing gap between information production and the ability to store data. DNA is a clear example of effective archival data storage in molecular form. In this Review, we provide an overview of the process, the state of the art in this area and challenges for mainstream adoption. We also survey the field of in vivo molecular memory systems that record and store information within the DNA of living cells, which, together with in vitro DNA data storage, lie at the growing intersection of computer systems and biotechnology.
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Affiliation(s)
- Luis Ceze
- Paul G. Allen School of Computer Science and Engineering, University of Washington, Seattle, WA, USA.
| | - Jeff Nivala
- Paul G. Allen School of Computer Science and Engineering, University of Washington, Seattle, WA, USA
| | - Karin Strauss
- Paul G. Allen School of Computer Science and Engineering, University of Washington, Seattle, WA, USA.,Microsoft Research, Redmond, WA, USA
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81
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Synthetic biology for improving cell fate decisions and tissue engineering outcomes. Emerg Top Life Sci 2019; 3:631-643. [PMID: 33523179 DOI: 10.1042/etls20190091] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 10/02/2019] [Accepted: 10/07/2019] [Indexed: 02/07/2023]
Abstract
Synthetic biology is a relatively new field of science that combines aspects of biology and engineering to create novel tools for the construction of biological systems. Using tools within synthetic biology, stem cells can then be reprogrammed and differentiated into a specified cell type. Stem cells have already proven to be largely beneficial in many different therapies and have paved the way for tissue engineering and regenerative medicine. Although scientists have made great strides in tissue engineering, there still remain many questions to be answered in regard to regeneration. Presented here is an overview of synthetic biology, common tools built within synthetic biology, and the way these tools are being used in stem cells. Specifically, this review focuses on how synthetic biologists engineer genetic circuits to dynamically control gene expression while also introducing emerging topics such as genome engineering and synthetic transcription factors. The findings mentioned in this review show the diverse use of stem cells within synthetic biology and provide a foundation for future research in tissue engineering with the use of synthetic biology tools. Overall, the work done using synthetic biology in stem cells is in its early stages, however, this early work is leading to new approaches for repairing diseased and damaged tissues and organs, and further expanding the field of tissue engineering.
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82
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Campa CC, Weisbach NR, Santinha AJ, Incarnato D, Platt RJ. Multiplexed genome engineering by Cas12a and CRISPR arrays encoded on single transcripts. Nat Methods 2019; 16:887-893. [PMID: 31406383 DOI: 10.1038/s41592-019-0508-6] [Citation(s) in RCA: 151] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Accepted: 06/07/2019] [Indexed: 12/28/2022]
Abstract
The ability to modify multiple genetic elements simultaneously would help to elucidate and control the gene interactions and networks underlying complex cellular functions. However, current genome engineering technologies are limited in both the number and the type of perturbations that can be performed simultaneously. Here, we demonstrate that both Cas12a and a clustered regularly interspaced short palindromic repeat (CRISPR) array can be encoded in a single transcript by adding a stabilizer tertiary RNA structure. By leveraging this system, we illustrate constitutive, conditional, inducible, orthogonal and multiplexed genome engineering of endogenous targets using up to 25 individual CRISPR RNAs delivered on a single plasmid. Our method provides a powerful platform to investigate and orchestrate the sophisticated genetic programs underlying complex cell behaviors.
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Affiliation(s)
- Carlo C Campa
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - Niels R Weisbach
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - António J Santinha
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - Danny Incarnato
- Department of Molecular Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, the Netherlands
| | - Randall J Platt
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland.
- Department of Chemistry, University of Basel, Basel, Switzerland.
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83
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Abstract
DNA outperforms most conventional storage media in terms of information retention time, physical density, and volumetric coding capacity. Advances in synthesis and sequencing technologies have enabled implementations of large synthetic DNA databases with impressive storage capacity and reliable data recovery. Several robust DNA storage architectures featuring random access, error correction, and content rewritability have been constructed with the potential for scalability and cost reduction. We survey these recent achievements and discuss alternative routes for overcoming the hurdles of engineering practical DNA storage systems. We also review recent exciting work on in vivo DNA memory including intracellular recorders constructed by programmable genome editing tools. Besides information storage, DNA could serve as a versatile molecular computing substrate. We highlight several state-of-the-art DNA computing techniques such as strand displacement, localized hybridization chain reactions, and enzymatic reaction networks. We summarize how these simple primitives have facilitated rational designs and implementations of in vitro DNA reaction networks that emulate digital/analog circuits, artificial neural networks, or nonlinear dynamic systems. We envision these modular primitives could be strategically adapted for sophisticated database operations and massively parallel computations on DNA databases. We also highlight in vivo DNA computing modules such as CRISPR logic gates for building scalable genetic circuits in living cells. To conclude, we discuss various implications and challenges of DNA-based storage and computing, and we particularly encourage innovative work on bridging these two areas of research to further explore molecular parallelism and near-data processing. Such integrated molecular systems could lead to far-reaching applications in biocomputing, security, and medicine.
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84
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Zhao J, Pokhilko A, Ebenhöh O, Rosser SJ, Colloms SD. A single-input binary counting module based on serine integrase site-specific recombination. Nucleic Acids Res 2019; 47:4896-4909. [PMID: 30957849 PMCID: PMC6511857 DOI: 10.1093/nar/gkz245] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 03/24/2019] [Accepted: 03/26/2019] [Indexed: 01/09/2023] Open
Abstract
A device that counts and records the number of events experienced by an individual cell could have many uses in experimental biology and biotechnology. Here, we report a DNA-based 'latch' that switches between two states upon each exposure to a repeated stimulus. The key component of the latch is a DNA segment whose orientation is inverted by the actions of ϕC31 integrase and its recombination directionality factor (RDF). Integrase expression is regulated by an external input, while RDF expression is controlled by the state of the latch, such that the orientation of the invertible segment switches efficiently each time the device receives an input pulse. Recombination occurs over a time scale of minutes after initiation of integrase expression. The latch requires a delay circuit, implemented with a transcriptional repressor expressed in only one state, to ensure that each input pulse results in only one inversion of the DNA segment. Development and optimization of the latch in living cells was driven by mathematical modelling of the recombination reactions and gene expression regulated by the switch. We discuss how N latches built with orthogonal site-specific recombination systems could be chained together to form a binary ripple counter that could count to 2N - 1.
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Affiliation(s)
- Jia Zhao
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, Bower Building, Glasgow G12 8QQ, Scotland
| | - Alexandra Pokhilko
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, Bower Building, Glasgow G12 8QQ, Scotland
| | - Oliver Ebenhöh
- Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich-Heine-University, Universitätsstraße 1, D-40225 Düsseldorf, Germany,Institute of Quantitative and Theoretical Biology, Heinrich-Heine-University Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
| | - Susan J Rosser
- SynthSys - Synthetic and Systems Biology, School of Biological Sciences, University of Edinburgh, CH Waddington Building, The King’s Buildings, Mayfield Road, Edinburgh EH9 3JD, Scotland,Correspondence may also be addressed to Susan J. Rosser. Tel. +44 131 650 50 86;
| | - Sean D Colloms
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, Bower Building, Glasgow G12 8QQ, Scotland,To whom correspondence should be addressed. Tel: +44 141 330 6236; Fax: +44 141 330 4878;
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