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- Creators: Barrett, The Honors College
- Creators: Brafman, David
Description
The portability of genetic tools from one organism to another is a cornerstone of synthetic biology. The shared biological language of DNA-to-RNA-to-protein allows for expression of polypeptide chains in phylogenetically distant organisms with little modification. The tools and contexts are diverse, ranging from catalytic RNAs in cell-free systems to bacterial proteins expressed in human cell lines, yet they exhibit an organizing principle: that genes and proteins may be treated as modular units that can be moved from their native organism to a novel one. However, protein behavior is always unpredictable; drop-in functionality is not guaranteed.
My work characterizes how two different classes of tools behave in new contexts and explores methods to improve their functionality: 1. CRISPR/Cas9 in human cells and 2. quorum sensing networks in Escherichia coli.
1. The genome-editing tool CRISPR/Cas9 has facilitated easily targeted, effective, high throughput genome editing. However, Cas9 is a bacterially derived protein and its behavior in the complex microenvironment of the eukaryotic nucleus is not well understood. Using transgenic human cell lines, I found that gene-silencing heterochromatin impacts Cas9’s ability to bind and cut DNA in a site-specific manner and I investigated ways to improve CRISPR/Cas9 function in heterochromatin.
2. Bacteria use quorum sensing to monitor population density and regulate group behaviors such as virulence, motility, and biofilm formation. Homoserine lactone (HSL) quorum sensing networks are of particular interest to synthetic biologists because they can function as “wires” to connect multiple genetic circuits. However, only four of these networks have been widely implemented in engineered systems. I selected ten quorum sensing networks based on their HSL production profiles and confirmed their functionality in E. coli, significantly expanding the quorum sensing toolset available to synthetic biologists.
My work characterizes how two different classes of tools behave in new contexts and explores methods to improve their functionality: 1. CRISPR/Cas9 in human cells and 2. quorum sensing networks in Escherichia coli.
1. The genome-editing tool CRISPR/Cas9 has facilitated easily targeted, effective, high throughput genome editing. However, Cas9 is a bacterially derived protein and its behavior in the complex microenvironment of the eukaryotic nucleus is not well understood. Using transgenic human cell lines, I found that gene-silencing heterochromatin impacts Cas9’s ability to bind and cut DNA in a site-specific manner and I investigated ways to improve CRISPR/Cas9 function in heterochromatin.
2. Bacteria use quorum sensing to monitor population density and regulate group behaviors such as virulence, motility, and biofilm formation. Homoserine lactone (HSL) quorum sensing networks are of particular interest to synthetic biologists because they can function as “wires” to connect multiple genetic circuits. However, only four of these networks have been widely implemented in engineered systems. I selected ten quorum sensing networks based on their HSL production profiles and confirmed their functionality in E. coli, significantly expanding the quorum sensing toolset available to synthetic biologists.
ContributorsDaer, René (Author) / Haynes, Karmella (Thesis advisor) / Brafman, David (Committee member) / Nielsen, David (Committee member) / Kiani, Samira (Committee member) / Arizona State University (Publisher)
Created2017
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
Conservatism is intrinsic to safety of emerging biotechnologies. Fear of unintended consequences, misuse, and bioterror are rightfully essential in our discussions of novel innovations. Clustered regularly Interspaced Short Palindromic Repeats (CRISPR) and its associated proteins are no exception. This review will characterize environmental and health-related risks of CRISPR-applications and expound upon mechanisms that are or can be used to minimize risk. CRISPR is broadening access and simplifying genomic and transcriptomic editing leading to wide-range usage in all of biology. Utilization in gene therapies, gene drives, and agriculture could all be universally impactful applications that need their own safety technologies and guidelines. The initial ethical guidelines and recommendations, that will guide these technologies, are being steadily developed. However, technical advances are required to facilitate safe usage. Since the advent of CRISPR gene editing in 2012 advances to limit off-target edits (both cellular and genomic) have been developed. Delivery systems that use viral or nanoparticle packaging incorporate safety mechanisms to guard against undesirable side effects are being produced and rigorously tested. Besides its applications in basic biology and potential as a gene therapy, CRISPR had humbler beginnings. Industrially it was, albeit unknowingly, used to fend off infection in productions of yogurt batches. This was one of the earliest applications of CRISPR, however with the knowledge we now have ecological and industrial uses of CRISPR have multiplied. Gene drives have the power to spread genetic mutations throughout populations and agricultural uses to better crop genomes are also of interest. These uses have struck a chord with interest groups (environmentalists, anti-GMO groups, etc) who imagine how this technology can drastically alter species with unforeseen evolutionary changes that could reshape present-day ecosystems. This review will describe existing technologies that will safeguard humanity and its interests while fully employing CRISPRs far-reaching potentiality.
ContributorsPineda, Michael (Author) / Kiani, Samira (Thesis director) / Ebrahimkhani, Mo (Committee member) / School of Life Sciences (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
Malaria is a disease that has plagued human populations throughout history. Malaria is cause by the parasite Plasmodium, which uses mosquitoes as a vector for transfer. Current methods for controlling malaria include issuing bed nets to citizens, spraying home with insecticides, and reactive medical care. However, using Clustered Regularly Interspaced Short Palindromic repeats (CRISPR) in conjunction with the Cas9 protein found in bacteria, the genomes of mosquitoes can be edited to remove the ability of mosquitoes to host Plasmodium or to create sex bias in which the birth rate of males is increased so as to make reproduction near impossible. Using CRISPR, this genome edit can be ‘driven’ through a population by increasing the likelihood of that gene being passed onto subsequent generations until the entire population possesses that gene; a gene drive can theoretically be used to eliminate malaria around the world. This paper identifies uncertainties concerning scientific, environmental, governance, economic ,and social aspects of researching and implementing gene drives and makes recommendations concerning these areas for the emerging technology of gene drives concerning the eradication of malaria using Sub-Saharan Africa as a case study
ContributorsSacco, Elena Maria (Author) / Frow, Emma (Thesis director) / Maynard, Andrew (Committee member) / School of Politics and Global Studies (Contributor) / School of International Letters and Cultures (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
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
Alzheimer’s disease (AD), despite over a century of research, does not have a clearly defined pathogenesis for the sporadic form that makes up the majority of disease incidence. A variety of correlative risk factors have been identified, including the three isoforms of apolipoprotein E (ApoE), a cholesterol transport protein in the central nervous system. ApoE ε3 is the wild-type variant with no effect on risk. ApoE ε2, the protective and most rare variant, reduces risk of developing AD by 40%. ApoE ε4, the risk variant, increases risk by 3.2-fold and 14.9-fold for heterozygous and homozygous representation respectively. Study of these isoforms has been historically complex, but the advent of human induced pluripotent stem cells (hiPSC) provides the means for highly controlled, longitudinal in vitro study. The effect of ApoE variants can be further elucidated using this platform by generating isogenic hiPSC lines through precise genetic modification, the objective of this research. As the difference between alleles is determined by two cytosine-thymine polymorphisms, a specialized CRISPR/Cas9 system for direct base conversion was able to be successfully employed. The base conversion method for transitioning from the ε3 to ε2 allele was first verified using the HEK293 cell line as a model with delivery via electroporation. Following this verification, the transfection method was optimized using two hiPSC lines derived from ε4/ε4 patients, with a lipofection technique ultimately resulting in successful base conversion at the same site verified in the HEK293 model. Additional research performed included characterization of the pre-modification genotype with respect to likely off-target sites and methods of isolating clonal variants.
ContributorsLakers, Mary Frances (Author) / Brafman, David (Thesis advisor) / Haynes, Karmella (Committee member) / Wang, Xiao (Committee member) / Arizona State University (Publisher)
Created2017
Description
CRISPR-Cas based DNA precision genome editing tools such as DNA Adenine Base Editors (ABEs) could remedy the majority of human genetic diseases caused by point mutations (aka Single Nucleotide Polymorphisms, SNPs). ABEs were designed by fusing CRISPR-Cas9 and DNA deaminating enzymes. Since there is no natural enzyme able to deaminate adenosine in DNA, the deaminase domain of ABE was evolved from an Escherichia coli tRNA deaminase, EcTadA. Initial rounds of directed evolution resulted in ABE7.10 enzyme (which contains two deaminases EcTadA and TadA7.10 fused to Cas9) which was further evolved to ABE8e containing a single TadA8e and Cas9. The original EcTadA as well as the evolved TadA8e where shown to form homodimers in solution. Although it was shown that tRNA binding pocket in EcTadA is composed by both monomers, the significance of TadA dimerization in either tRNA or DNA deamination has not been demonstrated. Here we explore the role of TadA dimerization on the DNA adenosine deamination activity of ABE8e. We hypothesize that the dimerization of TadA8e is more important for the DNA deamination than for the tRNA deamination. To explore this, I conducted a urea titration on ABE8e to disrupt TadA8e dimerization and performed single turnover kinetics assays to assess DNA deamination rate of ABE8e’s. Results showed that DNA deamination rate and efficiency of ABE8e was already impaired at 4M urea and completely lost at 7M. Unfortunately, CD measurements at the equivalent urea concentrations indicate that the loss of activity is due to the unfolding of ABE8e rather than the disruption of TadA8e’s dimerization.
ContributorsBennett, Marisa (Author) / Lapinaite, Audrone (Thesis director) / Mills, Jeremy (Committee member) / Stephanopolous, Nicholas (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / School of Molecular Sciences (Contributor)
Created2023-05
Description
A mutation rate refers to the frequency at which DNA mutations occur in an organism over time. In organisms, mutations are the ultimate source of genetic variation on which selection may act. However, a large number of mutations over time can be detrimental to the cell. Mutation rates are the frequency at which these new mutations arise over time. This can give great insight into DNA repair mechanisms abilities as well as the mutagenic abilities of selected factors. CRISPR-Cas9 is a powerful tool for genome editing, but its off-target effects are not yet fully understood and studied. With its increasing implementation in science and medicine, it is crucial to understand the mutagenic potential of the tool. S. cerevisiae is a model organism for studying genetics due to its fast growth rate and eukaryotic nature. By integrating CRISPR-Cas9 systems into S. cerevisiae, the mutational burden of the technology can be measured and quantified using fluctuation assays. In this experiment, a fluctuation assay using canavanine selective plates was conducted to determine the mutational burden of CRISPR-Cas9 in S. cerevisiae. Multiple trials revealed that various strains of CRISPR-Cas9 had a mutation rate up to 3-fold higher than that of wild-type S. cerevisiae. This information is essential in improving the precision and safety of CRISPR-Cas9 editing in various applications, including gene therapy and biotechnology.
ContributorsBrown, Adalyn (Author) / Lyncg, Michael (Thesis director) / Geiler-Samerotte, Kerry (Committee member) / Barrett, The Honors College (Contributor) / Department of English (Contributor) / School of Life Sciences (Contributor)
Created2023-05
Description
The purpose of this experiment is to deliver DNA origami barrels loaded with Cas13d-gRNA binary complexes to HPV-16 and HPV-18 cervical cancer lines to make the cancer mortal. The production of Cas 13d has proven successful with a concentration of ~ 1mg/mL, but the activity assay performed has not shown conclusive evidence of Cas13d and guide RNA binary complex formation or activity. Successful annealing of the DNA origami barrel has been quantified by an agarose gel, but further quantification by TEM is in progress. Overall, steady progress is being made towards the goal of targeting HPV16 E6/E7 pre-mRNA with CRISPR/Cas13d.
ContributorsGamoth, Yash (Author) / Anderson, Karen (Thesis director) / Chu, Po Lin (Committee member) / Lapinaite, Audrone (Committee member) / Barrett, The Honors College (Contributor) / School of Molecular Sciences (Contributor) / Dean, W.P. Carey School of Business (Contributor)
Created2023-05