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- All Subjects: Synthetic Biology
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Description
Recombinases are powerful tools for genome engineering and synthetic biology, however recombinases are limited by a lack of user-programmability and often require complex directed-evolution experiments to retarget specificity. Conversely, CRISPR systems have extreme versatility yet can induce off-target mutations and karyotypic destabilization. To address these constraints we developed an RNA-guided recombinase protein by fusing a hyperactive mutant resolvase from transposon TN3 to catalytically inactive Cas9. We validated recombinase-Cas9 (rCas9) function in model eukaryote Saccharomyces cerevisiae using a chromosomally integrated fluorescent reporter. Moreover, we demonstrated cooperative targeting by CRISPR RNAs at spacings of 22 or 40bps is necessary for directing recombination. Using PCR and Sanger sequencing, we confirmed rCas9 targets DNA recombination. With further development we envision rCas9 becoming useful in the development of RNA-programmed genetic circuitry as well as high-specificity genome engineering.
ContributorsStandage-Beier, Kylie S (Author) / Wang, Xiao (Thesis advisor) / Brafman, David A (Committee member) / Tian, Xiao-jun (Committee member) / Arizona State University (Publisher)
Created2018
Description
Synthetic biology is an emerging field which melds genetics, molecular biology, network theory, and mathematical systems to understand, build, and predict gene network behavior. As an engineering discipline, developing a mathematical understanding of the genetic circuits being studied is of fundamental importance. In this dissertation, mathematical concepts for understanding, predicting, and controlling gene transcriptional networks are presented and applied to two synthetic gene network contexts. First, this engineering approach is used to improve the function of the guide ribonucleic acid (gRNA)-targeted, dCas9-regulated transcriptional cascades through analysis and targeted modification of the RNA transcript. In so doing, a fluorescent guide RNA (fgRNA) is developed to more clearly observe gRNA dynamics and aid design. It is shown that through careful optimization, RNA Polymerase II (Pol II) driven gRNA transcripts can be strong enough to exhibit measurable cascading behavior, previously only shown in RNA Polymerase III (Pol III) circuits. Second, inherent gene expression noise is used to achieve precise fractional differentiation of a population. Mathematical methods are employed to predict and understand the observed behavior, and metrics for analyzing and quantifying similar differentiation kinetics are presented. Through careful mathematical analysis and simulation, coupled with experimental data, two methods for achieving ratio control are presented, with the optimal schema for any application being dependent on the noisiness of the system under study. Together, these studies push the boundaries of gene network control, with potential applications in stem cell differentiation, therapeutics, and bio-production.
ContributorsMenn, David J (Author) / Wang, Xiao (Thesis advisor) / Kiani, Samira (Committee member) / Haynes, Karmella (Committee member) / Nielsen, David (Committee member) / Marshall, Pamela (Committee member) / Arizona State University (Publisher)
Created2018
Description
The highly predictable structural and thermodynamic behavior of deoxynucleic acid (DNA) and ribonucleic acid (RNA) have made them versatile tools for creating artificial nanostructures over broad range. Moreover, DNA and RNA are able to interact with biological ligand as either synthetic aptamers or natural components, conferring direct biological functions to the nucleic acid devices. The applications of nucleic acids greatly relies on the bio-reactivity and specificity when applied to highly complexed biological systems.
This dissertation aims to 1) develop new strategy to identify high affinity nucleic acid aptamers against biological ligand; and 2) explore highly orthogonal RNA riboregulators in vivo for constructing multi-input gene circuits with NOT logic. With the aid of a DNA nanoscaffold, pairs of hetero-bivalent aptamers for human alpha thrombin were identified with ultra-high binding affinity in femtomolar range with displaying potent biological modulations for the enzyme activity. The newly identified bivalent aptamers enriched the aptamer tool box for future therapeutic applications in hemostasis, and also the strategy can be potentially developed for other target molecules. Secondly, by employing a three-way junction structure in the riboregulator structure through de-novo design, we identified a family of high-performance RNA-sensing translational repressors that down-regulates gene translation in response to cognate RNAs with remarkable dynamic range and orthogonality. Harnessing the 3WJ repressors as modular parts, we integrate them into biological circuits that execute universal NAND and NOR logic with up to four independent RNA inputs in Escherichia coli.
This dissertation aims to 1) develop new strategy to identify high affinity nucleic acid aptamers against biological ligand; and 2) explore highly orthogonal RNA riboregulators in vivo for constructing multi-input gene circuits with NOT logic. With the aid of a DNA nanoscaffold, pairs of hetero-bivalent aptamers for human alpha thrombin were identified with ultra-high binding affinity in femtomolar range with displaying potent biological modulations for the enzyme activity. The newly identified bivalent aptamers enriched the aptamer tool box for future therapeutic applications in hemostasis, and also the strategy can be potentially developed for other target molecules. Secondly, by employing a three-way junction structure in the riboregulator structure through de-novo design, we identified a family of high-performance RNA-sensing translational repressors that down-regulates gene translation in response to cognate RNAs with remarkable dynamic range and orthogonality. Harnessing the 3WJ repressors as modular parts, we integrate them into biological circuits that execute universal NAND and NOR logic with up to four independent RNA inputs in Escherichia coli.
ContributorsZhou, Yu (Ph.D.) (Author) / Yan, Hao (Thesis advisor) / Green, Alexander (Thesis advisor) / Woodbury, Neal (Committee member) / Ros, Alexandra (Committee member) / Arizona State University (Publisher)
Created2019
Description
Currently in synthetic biology only the Las, Lux, and Rhl quorum sensing pathways have been adapted for broad engineering use. Quorum sensing allows a means of cell to cell communication in which a designated sender cell produces quorum sensing molecules that modify gene expression of a designated receiver cell. While useful, these three quorum sensing pathways exhibit a nontrivial level of crosstalk, hindering robust engineering and leading to unexpected effects in a given design. To address the lack of orthogonality among these three quorum sensing pathways, previous scientists have attempted to perform directed evolution on components of the quorum sensing pathway. While a powerful tool, directed evolution is limited by the subspace that is defined by the protein. For this reason, we take an evolutionary biology approach to identify new orthogonal quorum sensing networks and test these networks for cross-talk with currently-used networks. By charting characteristics of acyl homoserine lactone (AHL) molecules used across quorum sensing pathways in nature, we have identified favorable candidate pathways likely to display orthogonality. These include Aub, Bja, Bra, Cer, Esa, Las, Lux, Rhl, Rpa, and Sin, which we have begun constructing and testing. Our synthetic circuits express GFP in response to a quorum sensing molecule, allowing quantitative measurement of orthogonality between pairs. By determining orthogonal quorum sensing pairs, we hope to identify and adapt novel quorum sensing pathways for robust use in higher-order genetic circuits.
ContributorsMuller, Ryan (Author) / Haynes, Karmella (Thesis director) / Wang, Xiao (Committee member) / Barrett, The Honors College (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Department of Chemistry and Biochemistry (Contributor) / School of Life Sciences (Contributor)
Created2015-05
Description
Synthetic biology is an emerging engineering disciple, which designs and controls biological systems for creation of materials, biosensors, biocomputing, and much more. To better control and engineer these systems, modular genetic components which allow for highly specific and high dynamic range genetic regulation are necessary. Currently the field struggles to demonstrate reliable regulators which are programmable and specific, yet also allow for a high dynamic range of control. Inspired by the characteristics of the RNA toehold switch in E. coli, this project attempts utilize artificial introns and complementary trans-acting RNAs for gene regulation in a eukaryote host, S. cerevisiae. Following modification to an artificial intron, splicing control with RNA hairpins was demonstrated. Temperature shifts led to increased protein production likely due to increased splicing due to hairpin loosening. Progress is underway to demonstrate trans-acting RNA interaction to control splicing. With continued development, we hope to provide a programmable, specific, and effective means for translational gene regulation in S. cerevisae.
ContributorsDorr, Brandon Arthur (Author) / Wang, Xiao (Thesis director) / Green, Alexander (Committee member) / Harrington Bioengineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The ability to edit chromosomal regions is an important tool for the study of gene function and the ability to engineer synthetic gene networks. CRISPR-Cas systems, a bacterial RNA-guided immune system against foreign nucleic acids, have recently been engineered for a plethora of genome engineering and transcriptional regulation applications. Here we employ engineered variants of CRISPR systems in proof-of-principle experiments demonstrating the ability of CRISPR-Cas derived single-DNA-strand cutting enzymes (nickases) to direct host-cell genomic recombination. E.coli is generally regarded as a poorly recombinogenic host with double-stranded DNA breaks being highly lethal. However, CRISPR-guided nickase systems can be easily programmed to make very precise, non-lethal, incisions in genomic regions directing both single reporter gene and larger-scale recombination events deleting up to 36 genes. Genome integrated repetitive elements of variable sizes can be employed as sites for CRISPR induced recombination. We project that single-stranded based editing methodologies can be employed alongside preexisting genome engineering techniques to assist and expedite metabolic engineering and minimalized genome research.
ContributorsStandage-Beier, Kylie S (Author) / Wang, Xiao (Thesis director) / Haynes, Karmella (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2014-05
Description
Measles and mumps are highly contagious, vaccine-preventable diseases with cases continuing to persist in high two-dose vaccinated populations. Recent outbreaks on university and college campuses across the United States prompt a need for further understanding of the immunity levels afforded by the MMR vaccine which has significantly decreased incidence rates of measles and mumps since it was introduced.
Current methods for IgG antibody detection include enzyme immunoassays (EIA) such as the commercially available Diamedix Immunosimplicity® Measles IgG test kit and the Diamedix Immunosimplicity® Mumps IgG test kit. EIAs generally provide high sensitivity and strong specificity, however, there is a need for rapid screening of measles and mumps specific immunity in outbreak and resource-limited areas which could be solved by use a point-of-care (POC) platform.
This study aims to optimize a point-of-care device for the multiplexed detection of MeV, MuV, and RuV IgG antibodies in sera and to compare the sensitivity to commercial enzyme immunoassays. The IgG antibody levels to MeV and MuV were measured using EIA test kits for a total of 44 healthy serum samples. Of the samples, 6% were seronegative for MeV-specific IgG antibodies and 75% were seronegative for MuV-specific antibodies, showing low correlation of IgG antibody levels between both viruses.
To improve the sensitivity of the POC device, multiple conjugated fluorescent secondary antibodies were tested with different surface chemistries. Signal detection was measured using the pre-developed four-site slide reader. Preliminary data show that Nile Red microspheres provide robust signal detection and should be the secondary antibody of choice when sera are tested for IgG antibodies using the POC platform in future work.
Current methods for IgG antibody detection include enzyme immunoassays (EIA) such as the commercially available Diamedix Immunosimplicity® Measles IgG test kit and the Diamedix Immunosimplicity® Mumps IgG test kit. EIAs generally provide high sensitivity and strong specificity, however, there is a need for rapid screening of measles and mumps specific immunity in outbreak and resource-limited areas which could be solved by use a point-of-care (POC) platform.
This study aims to optimize a point-of-care device for the multiplexed detection of MeV, MuV, and RuV IgG antibodies in sera and to compare the sensitivity to commercial enzyme immunoassays. The IgG antibody levels to MeV and MuV were measured using EIA test kits for a total of 44 healthy serum samples. Of the samples, 6% were seronegative for MeV-specific IgG antibodies and 75% were seronegative for MuV-specific antibodies, showing low correlation of IgG antibody levels between both viruses.
To improve the sensitivity of the POC device, multiple conjugated fluorescent secondary antibodies were tested with different surface chemistries. Signal detection was measured using the pre-developed four-site slide reader. Preliminary data show that Nile Red microspheres provide robust signal detection and should be the secondary antibody of choice when sera are tested for IgG antibodies using the POC platform in future work.
ContributorsBharaj, Tirinder K. (Author) / Anderson, Karen (Thesis director) / Green, Alexander (Committee member) / Ewaisha, Radwa (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Extensive efforts have been made to develop efficient and low-cost methods for diagnostics to identify molecular biomarkers that are linked to a wide array of conditions, including cancer. A highly developed method includes utilizing the gene-editing enzyme CRISPR-Cas12a (Cpf1), which demonstrates double-stranded DNase activity with RuvC catalytic domain with high sensitivity and specificity. This DNase activity is RNA-guided and requires a T-rich PAM site on the target sequence for functional cleavage. There have been recent efforts to utilize this DNase activity of Cas12a by combining it with isothermal amplification and analysis by lateral strip tests. This project examined CRISPR-based early detection of microRNA biomarkers. MicroRNA are short RNA molecules that have large roles in post-transcriptional gene regulation. However, due the short length of microRNA and its single-stranded nature, it is challenging to use Cas12a for microRNA detection using existing methods. Thus, this project investigated the potential of two microRNA detection strategies for recognition by CRISPR-Cas12a. These methods were microRNA-splinted ligation with polymerase chain reaction (PCR) and MicroRNA-specific reverse transcriptase PCR (RT-PCR). Gel imaging demonstrated effective amplification of ligated DNA through microRNA-splinted ligation with PCR/RPA. In addition, lateral strips tests showed effective cleavage of the target sequences by Cas12a. However, RT-PCR method demonstrated low amplification by PCR and inefficient poly(A) elongation. This project paves the way for the detection of an extensive range of microRNA biomarkers that are linked to an array of diseases. Future directions include analysis and modifications of RT-PCR method to improve experimental results, extending these detection methods to a larger range of microRNA sequences, and eventually utilizing them for detection in human samples.
ContributorsStaren, Michael Steven (Author) / Green, Alexander (Thesis director) / Stephanopoulos, Nicholas (Committee member) / Diehnelt, Chris (Committee member) / School of Life Sciences (Contributor) / College of Health Solutions (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Synthetic biology is a novel method that reengineers functional parts of natural genes of interest to build new biomolecular devices able to express as designed. There is increasing interest in synthetic biology due to wide potential applications in various fields such as clinics and fuel production. However, there are still many challenges in synthetic biology. For example, many natural biological processes are poorly understood, and these could be more thoroughly studied through model synthetic gene networks. Additionally, since synthetic biology applications may have numerous design constraints, more inducer systems should be developed to satisfy different requirements for genetic design.
This thesis covers two topics. First, I attempt to generate stochastic resonance (SR) in a biological system. Synthetic bistable systems were chosen because the inducer range in which they exhibit bistability can satisfy one of the three requirements of SR: a weak periodic force is unable to make the transition between states happen. I synthesized several different bistable systems, including toggle switches and self-activators, to select systems matching another requirement: the system has a clear threshold between the two energy states. Their bistability was verified and characterized. At the same time, I attempted to figure out the third requirement for SR – an effective noise serving as the stochastic force – through one of the most widespread toggles, the mutual inhibition toggle, in both yeast and E. coli. A mathematic model for SR was written and adjusted.
Secondly, I began work on designing a new genetic system capable of responding to pulsed magnetic fields. The operators responding to pulsed magnetic stimuli in the rpoH promoter were extracted and reorganized. Different versions of the rpoH promoter were generated and tested, and their varying responsiveness to magnetic fields was recorded. In order to improve efficiency and produce better operators, a directed evolution method was applied with the help of a CRISPR-dCas9 nicking system. The best performing promoters thus far show a five-fold difference in gene expression between trials with and without the magnetic field.
This thesis covers two topics. First, I attempt to generate stochastic resonance (SR) in a biological system. Synthetic bistable systems were chosen because the inducer range in which they exhibit bistability can satisfy one of the three requirements of SR: a weak periodic force is unable to make the transition between states happen. I synthesized several different bistable systems, including toggle switches and self-activators, to select systems matching another requirement: the system has a clear threshold between the two energy states. Their bistability was verified and characterized. At the same time, I attempted to figure out the third requirement for SR – an effective noise serving as the stochastic force – through one of the most widespread toggles, the mutual inhibition toggle, in both yeast and E. coli. A mathematic model for SR was written and adjusted.
Secondly, I began work on designing a new genetic system capable of responding to pulsed magnetic fields. The operators responding to pulsed magnetic stimuli in the rpoH promoter were extracted and reorganized. Different versions of the rpoH promoter were generated and tested, and their varying responsiveness to magnetic fields was recorded. In order to improve efficiency and produce better operators, a directed evolution method was applied with the help of a CRISPR-dCas9 nicking system. The best performing promoters thus far show a five-fold difference in gene expression between trials with and without the magnetic field.
ContributorsHu, Hao (Author) / Wang, Xiao (Thesis advisor) / Stabenfeldt, Sarah (Committee member) / Brafman, David (Committee member) / Arizona State University (Publisher)
Created2016
Description
Based upon the idea of a "science fiction prototype" as originally designed by Brian David Johnson, Salomon’s House is a science fiction novella, written to be as scientifically accurate as possible and to present a balanced account of the potential social consequences of genetic engineering. It aims to explore the answers to some core questions that have plagued scientists and philosophers alike while entertaining its readers with a punchy, character-driven narrative.
ContributorsMansfield, Izaac (Author) / Finn, Ed (Thesis director) / Frow, Emma (Committee member) / Barrett, The Honors College (Contributor) / Department of Information Systems (Contributor) / School for the Future of Innovation in Society (Contributor)
Created2023-05