68 research outputs found
Engineering microorganisms for synthesizing value-added products
No full textThe overall goal of my thesis research is to produce value-added products using engineered microorganisms. Recent developments in metabolic engineering have allowed us to improve endogenous metabolic pathways or introduce heterologous metabolic pathways into microorganisms so that the engineered microorganisms have desired properties and phenotypes. As a result, value-added products that can only be synthesized by chemical processes can be produced in a more economical and sustainable way through biological processes using engineered microorganisms.
Escherichia coli and Saccharomyces cerevisiae served as a biotechnological production organisms as well as a prokaryotic and eukaryotic model system in my thesis research, respectively. Since both strains are model strains, tremendous metabolic engineering tools and fermentation process techniques have already been developed and applied, but there are still more improvements that must be made to reach the titer and productivity of a target product for industrial scale production.
The first goal of my thesis study was to overcome the drawbacks of high-level expression of rate-limiting enzymes for improving target products production. Increasing the expression level of the rate limiting enzyme via overexpression of the gene negatively affects the viability of host strain, making it difficult to produce a target product in a sustainable way. Instead of increasing the copy number using a high-copy plasmid or improving the transcription level using a strong promoter, I simply deleted two genes without affecting host strain’s viability and obtained the improved titer and productivity of a target product (2’-Fucosyllactose) in engineered E. coli.
The second goal of my thesis study was to enhance the production of a target product (2’-fucosyllactose) in engineered S. cerevisiae by reducing by-product (ethanol) production. The second objective was based on three approaches. First, the primary carbon source was changed from glucose to xylose to minimize ethanol production as a by-product and maximize a target product production. Second, all heterologous enzyme needed for 2’-Fucosyllactose was chromosomally integrated an expressed by using CRISPR-Cas9 based genetic modification. Third, the heterologous gene was additionally integrated into chromosome to increase the enzymes activities expressed on chromosome.
The third goal of my thesis study was to effectively resolve without glycerol formation as a by-product the redox imbalance caused by the reduction or elimination of ethanol production. To produce other target products from glucose than ethanol, ethanol producing genes (PDC: pyruvate decarboxylase, ADH: acetaldehyde dehydrogenase) should be mitigated in S. cerevisiae. Due to the redox imbalance, S. cerevisiae exhibited low growth rate and glucose consumption rate, resulting in a failure to reach the productivity of a target product suitable for industrial scale production. Therefore, by introducing an alternative metabolic pathway that can efficiently oxidize cytosolic NADH, we aimed to improve the productivity of a target product without producing glycerol as a by-product.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-12-01The student, Jaewon Lee, accepted the attached license on 2019-12-03 at 16:46.The student, Jaewon Lee, submitted this Dissertation for approval on 2019-12-03 at 17:00.This Dissertation was approved for publication on 2019-12-04 at 13:41.DSpace SAF Submission Ingestion Package generated from Vireo submission #14678 on 2020-02-28 at 17:37:47Made available in DSpace on 2020-03-02T22:38:56Z (GMT). No. of bitstreams: 5
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Previous issue date: 2019-12-04Embargo set by: Seth Robbins for item 114025
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Operator spectroscopy for 4D SCFTs with a=c
No full textWe study a rich set of four-dimensional superconformal field theories with both central charges identical: a=c. These are constructed via the diagonal N=2 or N=1 gauging of the flavor symmetry G of a collection of N=2 Argyres-Douglas theories of type Dp(G), with or without adjoint chiral multiplets, in 2106.12579 and 2111.12092. We compute superconformal indices of some theories where the rank of G is low, performing a refined test for unitarity, and further determine the relevant and marginal operator content in detail. We find that most of these theories flow to interacting superconformal field theories with a=c in the infrared. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.
THE ROLE OF INTERLEUKIN-10 IN SEX DIFFERENCES IN PAIN AND LONG-TERM SUPPRESSION OF PAIN
No full textThesis (Ph.D.)--Michigan State University. Cell and Molecular Biology - Doctor of Philosophy, 2025Chronic pain is a prevalent disorder that compromises quality of life and imposes a burden on society. Increasing evidence indicates that the immune system can cause, worsen, prolong, or, conversely, resolve pain. In particular, interleukin (IL)-10 is a potent anti-inflammatory cytokine produced by immune cells including monocytes, macrophages, T cells, and B cells. Although IL-10 has been implicated in pain inhibition in both animals and humans, its pain-resolving mechanisms or cellular sources under pain conditions remain to be further elucidated. In my Ph.D. dissertation, I investigated the role of IL-10 in 1) sex differences in pain resolution in an inflammatory pain model and 2) long-term pain suppression in chemotherapy-induced neuropathic pain. 1) During skin inflammation, IL-10 in the inflamed skin resolves pain by signaling through IL-10R1+ sensory nerves innervating the skin. IL-10 is primarily produced by infiltrating monocytes, and IL-10+ monocytes serve as potent drivers of pain resolution. These cells are more abundant in males than females, which contributes to sex differences in pain resolution. The male predominance of IL-10+ monocytes is regulated by sex hormones, particularly androgen signaling, which promotes IL-10 production in monocytes. Altogether, androgen signaling enables the greater abundance of IL-10+ monocytes in males resulting in faster pain resolution compared with females. 2) In chemotherapy-induced neuropathic pain model, I found that pain is being actively suppressed by IL-10 during ostensible pain recovery. IL-10 is continuously produced from spinal meningeal resident macrophages. Especially, IL-10R signaling in DRG sensory neurons is crucial to maintain IL-10-driven pain suppression. I further identified that long-term pain suppression is driven by upregulation of \u3b4OR in DRG neurons, driven by IL-10. Collectively, my result shows that IL-10 upregulated \u3b4OR in DRG to maintain remission of pain. Overall, these dissertation studies advance our understanding of IL-10-mediated crosstalk between immune cells and pain-sensing neurons, providing new insights into promising therapeutic strategies for the treatment of chronic pain.Description based on online resource. Title from PDF t.p. (Michigan State University Fedora Repository, viewed ).Includes bibliographical references
The small GTPase ARF6 regulates GABAergic synapse development
No full textADP ribosylation factors (ARFs) are a family of small GTPases composed of six members (ARF1-6) that control various cellular functions, including membrane trafficking and actin cytoskeletal rearrangement, in eukaryotic cells. Among them, ARF1 and ARF6 are the most studied in neurons, particularly at glutamatergic synapses, but their roles at GABAergic synapses have not been investigated. Here, we show that a subset of ARF6 protein is localized at GABAergic synapses in cultured hippocampal neurons. In addition, we found that knockdown (KD) of ARF6, but not ARF1, triggered a reduction in the number of GABAergic synaptic puncta in mature cultured neurons in an ARF activity-dependent manner. ARF6 KD also reduced GABAergic synaptic density in the mouse hippocampal dentate gyrus (DG) region. Furthermore, ARF6 KD in the DG increased seizure susceptibility in an induced epilepsy model. Viewed together, our results suggest that modulating ARF6 and its regulators could be a therapeutic strategy against brain pathologies involving hippocampal network dysfunction, such as epilepsy. © 2020 The Author(s).1
IMPACT OF LEADERSHIP AND TEAM MEMBERS ’ INDIVIDUALISM- COLLECTIVISM ON TEAM PROCESSES AND OUTCOMES: A LEADER- MEMBER EXCHANGE PERSPECTIVE
No full textRights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author
Slitrk2 controls excitatory synapse development via PDZ-mediated protein interactions
No full textMembers of the Slitrk (Slit- and Trk-like protein) family of synaptic cell-adhesion molecules control excitatory and inhibitory synapse development through isoform-dependent extracellular interactions with leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-RPTPs). However, how Slitrks participate in activation of intracellular signaling pathways in postsynaptic neurons remains largely unknown. Here we report that, among the six members of the Slitrk family, only Slitrk2 directly interacts with the PDZ domain-containing excitatory scaffolds, PSD-95 and Shank3. The interaction of Slitrk2 with PDZ proteins is mediated by the cytoplasmic COOH-terminal PDZ domain-binding motif (Ile-Ser-Glu-Leu), which is not found in other Slitrks. Mapping analyses further revealed that a single PDZ domain of Shank3 is responsible for binding to Slitrk2. Slitrk2 forms in vivo complexes with membrane-associated guanylate kinase (MAGUK) family proteins in addition to PSD-95 and Shank3. Intriguingly, in addition to its role in synaptic targeting in cultured hippocampal neurons, the PDZ domain-binding motif of Slitrk2 is required for Slitrk2 promotion of excitatory synapse formation, transmission, and spine development in the CA1 hippocampal region. Collectively, our data suggest a new molecular mechanism for conferring isoform-specific regulatory actions of the Slitrk family in orchestrating intracellular signal transduction pathways in postsynaptic neurons. © 2019, The Author(s).1
Differentially altered social dominance- and cooperative-like behaviors in Shank2- and Shank3-mutant mice
No full textBackground: Recent progress in genomics has contributed to the identification of a large number of autism spectrum disorder (ASD) risk genes, many of which encode synaptic proteins. Our understanding of ASDs has advanced rapidly, partly owing to the development of numerous animal models. Extensive characterizations using a variety of behavioral batteries that analyze social behaviors have shown that a subset of engineered mice that model mutations in genes encoding Shanks, a family of excitatory postsynaptic scaffolding proteins, exhibit autism-like behaviors. Although these behavioral assays have been useful in identifying deficits in simple social behaviors, alterations in complex social behaviors remain largely untested. Methods: Two syndromic ASD mouse models—Shank2 constitutive knockout [KO] mice and Shank3 constitutive KO mice—were examined for alterations in social dominance and social cooperative behaviors using tube tests and automated cooperation tests. Upon naïve and salient behavioral experience, expression levels of c-Fos were analyzed as a proxy for neural activity across diverse brain areas, including the medial prefrontal cortex (mPFC) and a number of subcortical structures. Findings: As previously reported, Shank2 KO mice showed deficits in sociability, with intact social recognition memory, whereas Shank3 KO mice displayed no overt phenotypes. Strikingly, the two Shank KO mouse models exhibited diametrically opposed alterations in social dominance and cooperative behaviors. After a specific social behavioral experience, Shank mutant mice exhibited distinct changes in number of c-Fos+ neurons in the number of cortical and subcortical brain regions. Conclusions: Our results underscore the heterogeneity of social behavioral alterations in different ASD mouse models and highlight the utility of testing complex social behaviors in validating neurodevelopmental and neuropsychiatric disorder models. In addition, neural activities at distinct brain regions are likely collectively involved in eliciting complex social behaviors, which are differentially altered in ASD mouse models. © 2020, The Author(s).1
Low Temperature Measurement of the Electrical Conductivity in Amorphous InGaZnO Thin Films
No full textWe examine the temperature-dependent electrical conductivity in amorphous InGaZnO thin films with various cation compositions. In-rich films are metallic, while Ga-rich films are semiconducting with logarithmic conductivities linear to -T−1/4 above T = 60 K. The Zn-rich films are also semiconducting but have >102 times higher conductivity than the Ga-rich films. At T > 60 K, thermal electronic excitation dominantly contributes the conduction, while at T < 60 K, certain impurity scatterings or structural disorders have importance in the electrical properties in low carrier a-IGZO system.3311sciescopu
Loss of IQSEC3 Disrupts GABAergic Synapse Maintenance and Decreases Somatostatin Expression in the Hippocampus
No full textGephyrin interacts with various GABAergic synaptic proteins to organize GABAergic synapse development. Among the multitude of gephyrin-binding proteins is IQSEC3, a recently identified component at GABAergic synapses that acts through its ADP ribosylation factor-guanine nucleotide exchange factor (ARF-GEF) activity to orchestrate GABAergic synapse formation. Here, we show that IQSEC3 knockdown (KD) reduced GABAergic synaptic density in vivo, suggesting that IQSEC3 is required for GABAergic synapse maintenance in vivo. We further show that IQSEC3 KD in the dentate gyrus (DG) increases seizure susceptibility and triggers selective depletion of somatostatin (SST) peptides in the DG hilus in an ARF-GEP activity-dependent manner. Strikingly, selective introduction of SST into SST interneurons in DG-specific IQSEC3-KD mice reverses GABAergic synaptic deficits. Thus, our data suggest that IQSEC3 is required for linking gephyrin-GABAA receptor complexes with ARF-dependent pathways to prevent aberrant, runaway excitation and thereby contributes to the integrity of SST interneurons and proper GABAergic synapse maintenance. © 2020 The Author(s)
In this study, Kim et al. investigate the effect of loss of function of IQSEC3, a gephyrin-binding GABAergic synapse-specific ARF-GEF, using hippocampal dentate gyrus (DG)-specific IQSEC3-knockdown (KD) mice. Strikingly, IQSEC3 KD causes a massive reduction of somatostatin (SST) expression. The restricted SST expression in SST+ interneurons reverses the pathological phenotypes. © 2020 The Author(s)1
PTPσ Controls Presynaptic Organization of Neurotransmitter Release Machinery at Excitatory Synapses
No full textLeukocyte common antigen-related receptor tyrosine phosphatases (LAR-RPTPs) are evolutionarily conserved presynaptic organizers. The synaptic role of vertebrate LAR-RPTPs in vivo, however, remains unclear. In the current study, we analyzed the synaptic role of PTPσ using newly generated, single conditional knockout (cKO) mice targeting PTPσ. We found that the number of synapses was reduced in PTPσ cKO cultured neurons in association with impaired excitatory synaptic transmission, abnormal vesicle localization, and abnormal synaptic ultrastructure. Strikingly, loss of presynaptic PTPσ reduced neurotransmitter release prominently at excitatory synapses, concomitant with drastic reductions in excitatory innervations onto postsynaptic target areas in vivo. Furthermore, loss of presynaptic PTPσ in hippocampal CA1 pyramidal neurons had no impact on postsynaptic glutamate receptor responses in subicular pyramidal neurons. Postsynaptic PTPσ deletion had no effect on excitatory synaptic strength. Taken together, these results demonstrate that PTPσ is a bona fide presynaptic adhesion molecule that controls neurotransmitter release and excitatory inputs. © 2020 The Author(s)1
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