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Open Access Publications from the University of California

Scholarly Works (11 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2015)

This project uncovers the role of buses and their riders in shaping Los Angeles urban history in two crucial moments. First, while the private automobile inexorably altered American mobility, the bus quietly became the dominant form of public transit, replacing streetcars by the mid-1950s. I argue the jitney (the precursor to the bus, a short-lived owner/operator business phenomenon throughout the U.S. in the 1910s) directed the shift into automobile-based public transportation by giving riders a choice in transit, ultimately resulting in the end of interurban rail service. Secondly, the movement into public ownership of mass bus transit in the 1950s was inspired in part by riders, resulting in the municipally-directed systems we now find common. This decision to create publicly-owned public transportation occurred in the post-WWII context of Cold War fears of government oppression and socialism, marking transportation as something of an outlier in the cultural construction of social and municipal responsibility. Still, the limitations placed upon transit by Angelinos in the form of funding and planning failures ultimately reinforces the skepticism of government as a provider of services.

The dissertation intends to prove that riders directed the movement into road-based public transportation in a quest for more efficient transportation that met their needs more effectively than urban rail. It further analyzes the moral and ethical implications of why 1950s Los Angeles--amid a historical moment actively promoting private mobility in the form of massive federal and state highway programs--chose to assume public control of an erstwhile private industry. Public ownership changed the sort of access into transportation planning and operation, allowing ethical and moral issues (such as the social effect of fare increases, union activity, and unprofitable route service into low income areas) to challenge the dollars-and-cents approach to transportation planning previously, and unsuccessfully, embraced by private ownership. Although the boundaries placed upon public transit by citizens of Los Angeles ultimately emphasize ideas of limited government (in keeping with other Cold War-period studies of American culture), the assumption of public transportation under public ownership in the 1950s was an important change in the cultural interpretation of transit as a social responsibility, rather than a private entrepreneurial opportunity.

In each step of this dissertation, riders are the primary catalyst, directing the changes in transit through market forces, through choice in the technology they preferred, or through funding of transit projects. Despite all the urban planning and top-down transit schemes--private or public--riders retained the ability to reshape transit in L.A. in the twentieth century through each moment of the city's transportation history.

    Cover page: Jitneys, Buses, and Public Transportation in Twentieth Century Los Angeles
    • Thesis
    • Peer Reviewed
    UC Irvine Electronic Theses and Dissertations (2017)

    Over the past 30 years of experimental evolutionary research on Drosophila, strong functional associations have been established between organismal characters, life history, and behavior. Evolutionary physiologists use stress as a tool, either to measure an organism’s physical robustness, or to create differentiated populations with which to study adaptation. However, many questions are unanswered. For example, do short periods of strong selection generate similar levels of functional divergence to those generated by long-sustained selection? And if so, can we take the already advantageous Drosophila model system and use it to effectively study vertebrate diseases (i.e. cardiovascular disease and obesity-related disorders).

    Chapter 1 examines the relationship between evolutionary history and physiological differentiation. We observed classic physiological characters, specifically stress resistance and locomotion, as well as a character of recent interest, heart robustness. We found that short periods of strong selection applied to outbred Mendelian populations can readily generate high levels of functional differentiation.

    Chapter 2 revolves around the interrelationships among major physiological systems. By combining electrical pacing and flight exhaustion assays with manipulative conditioning, we started to unpack the interrelationships between cardiac function, flight endurance, and stress resistance. One major insight is the adverse impact of lipids on Drosophila heart robustness, a parallel result to many comparable studies in human cardiology.

    With human obesity growing to epidemic proportions in the United States, and excessive lipid accumulation being a risk factor for heart disease, we sought to observe the effects of lipid accumulation in Drosophila. Chapter 3 discusses the effects of intense selection for increased starvation resistance on ten outbred Drosophila populations. These populations displayed cardiac dysfunction, increased adult mortality, and elevated lipid levels, making them a useful model system for heart disease and obesity-related disorders. In Chapter 4, I emulated the effects of chronic consumption of the high-fat, high-caffeine fast-food diet by exposing flies to coconut oil and caffeine. Similarly, the findings here continue to support the general inference that high lipid levels present challenges for the Drosophila heart. Fruit flies could be an invaluable resource in understanding the molecular, genetic and other machinery underlying heart disease.

      Cover page: Evolutionary Physiology of Drosophila melanogaster
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2012)
      Leucine-rich repeat kinase 2 (LRRK2) is a large multidomain protein that contains enzymatically functional GTPase and kinase domains. Several noncoding LRRK2 gene polymorphisms have been associated with susceptibility to Parkinson's disease (PD), Crohn's disease, and leprosy. Many LRRK2 coding polymorphisms have been associated with or causally linked to PD. The G2019S point mutation within the LRRK2 kinase domain is the most common cause of familial PD. The G2019S mutation appears to alter LRRK2 kinase activity. Some but not all studies have reported that LRRK2 kinase activity is dependent upon LRRK2 dimerization and membrane localization. It is important to define the oligomeric state(s) of LRRK2 in living cells, which to date have only been characterized in vitro. Here we use confocal and total internal reflection microscopy coupled with number and brightness analysis to study the oligomeric states of LRRK2 within the cytosol and on the plasma membrane of live CHO-K1 cells. Our results show, for the first time to our knowledge, that LRRK2 is predominantly monomeric throughout the cytosol of living cells, but attains predominately higher oligomeric states in the plasma membrane.
        Cover page: Number and Brightness Analysis of LRRK2 Oligomerization in Live CellsCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2013)
          Cover page: Mutations Associated with Centronuclear Myopathy (CNM) Enhance the Size and Stability of Dynamin 2 Clusters in CellsCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2021)

          Aims

          In mammalian ventricles, electrical gradients establish electrical heterogeneities as essential tissue mechanisms to optimize mechanical efficiency and safeguard electrical stability. Electrical gradients shape mammalian electrocardiographic patterns; disturbance of electrical gradients is proarrhythmic. The zebrafish heart is a popular surrogate model for human cardiac electrophysiology thanks to its remarkable recapitulation of human electrocardiogram and ventricular action potential features. Yet, zebrafish ventricular electrical gradients are largely unexplored. The goal of this study is to define the zebrafish ventricular electrical gradients that shape the QRS complex and T wave patterns at baseline and under oxidative stress.

          Methods and results

          We performed in vivo electrocardiography and ex vivo voltage-sensitive fluorescent epicardial and transmural optical mapping of adult zebrafish hearts at baseline and during acute H2O2 exposure. At baseline, apicobasal activation and basoapical repolarization gradients accounted for the polarity concordance between the QRS complex and T wave. During H2O2 exposure, differential regional impairment of activation and repolarization at the apex and base disrupted prior to baseline electrical gradients, resulting in either reversal or loss of polarity concordance between the QRS complex and T wave. KN-93, a specific calcium/calmodulin-dependent protein kinase II inhibitor (CaMKII), protected zebrafish hearts from H2O2 disruption of electrical gradients. The protection was complete if administered prior to oxidative stress exposure.

          Conclusions

          Despite remarkable apparent similarities, zebrafish and human ventricular electrocardiographic patterns are mirror images supported by opposite electrical gradients. Like mammalian ventricles, zebrafish ventricles are also susceptible to H2O2 proarrhythmic perturbation via CaMKII activation. Our findings suggest that the adult zebrafish heart may constitute a clinically relevant model to investigate ventricular arrhythmias induced by oxidative stress. However, the fundamental ventricular activation and repolarization differences between the two species that we demonstrated in this study highlight the potential limitations when extrapolating results from zebrafish experiments to human cardiac electrophysiology, arrhythmias, and drug toxicities.
            Cover page: Adult zebrafish ventricular electrical gradients as tissue mechanisms of ECG patterns under baseline vs. oxidative stress.
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2014)

            Background

            Dynamin 2 (Dyn2) is a ~100kDa GTPase that assembles around the necks of nascent endocytic and Golgi vesicles and catalyzes membrane scission. Mutations in Dyn2 that cause centronuclear myopathy (CNM) have been shown to stabilize Dyn2 polymers against GTP-dependent disassembly in vitro. Precisely timed regulation of assembly and disassembly is believed to be critical for Dyn2 function in membrane vesiculation, and the CNM mutations interfere with this regulation by shifting the equilibrium toward the assembled state.

            Methods

            In this study we use two fluorescence fluctuation spectroscopy (FFS) approaches to show that a CNM mutant form of Dyn2 also has a greater propensity to self-assemble in the cytosol and on the plasma membrane of living cells.

            Results

            Results obtained using brightness analysis indicate that unassembled wild-type Dyn2 is predominantly tetrameric in the cytosol, although different oligomeric species are observed, depending on the concentration of expressed protein. In contrast, an R369W mutant identified in CNM patients forms higher-order oligomers at concentrations above 1μM. Investigation of Dyn2-R369W by Total Internal Reflection Fluorescence (TIRF) FFS reveals that this mutant forms larger and more stable clathrin-containing structures on the plasma membrane than wild-type Dyn2.

            Conclusions and general significance

            These observations may explain defects in membrane trafficking reported in CNM patient cells and in heterologous systems expressing CNM-associated Dyn2 mutants.
              Cover page: A mutation associated with centronuclear myopathy enhances the size and stability of dynamin 2 complexes in cellsCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2014)

              Background

              Dynamin 2 (Dyn2) is a ~100kDa GTPase that assembles around the necks of nascent endocytic and Golgi vesicles and catalyzes membrane scission. Mutations in Dyn2 that cause centronuclear myopathy (CNM) have been shown to stabilize Dyn2 polymers against GTP-dependent disassembly in vitro. Precisely timed regulation of assembly and disassembly is believed to be critical for Dyn2 function in membrane vesiculation, and the CNM mutations interfere with this regulation by shifting the equilibrium toward the assembled state.

              Methods

              In this study we use two fluorescence fluctuation spectroscopy (FFS) approaches to show that a CNM mutant form of Dyn2 also has a greater propensity to self-assemble in the cytosol and on the plasma membrane of living cells.

              Results

              Results obtained using brightness analysis indicate that unassembled wild-type Dyn2 is predominantly tetrameric in the cytosol, although different oligomeric species are observed, depending on the concentration of expressed protein. In contrast, an R369W mutant identified in CNM patients forms higher-order oligomers at concentrations above 1μM. Investigation of Dyn2-R369W by Total Internal Reflection Fluorescence (TIRF) FFS reveals that this mutant forms larger and more stable clathrin-containing structures on the plasma membrane than wild-type Dyn2.

              Conclusions and general significance

              These observations may explain defects in membrane trafficking reported in CNM patient cells and in heterologous systems expressing CNM-associated Dyn2 mutants.
                Cover page: A mutation associated with centronuclear myopathy enhances the size and stability of dynamin 2 complexes in cells
                • Article
                • Peer Reviewed
                UC San Francisco Previously Published Works (2015)

                Background

                The Activity-regulated cytoskeleton-associated protein, Arc, is an immediate-early gene product implicated in various forms of synaptic plasticity. Arc promotes endocytosis of AMPA type glutamate receptors and regulates cytoskeletal assembly in neuronal dendrites. Its role in endocytosis may be mediated by its reported interaction with dynamin 2, a 100 kDa GTPase that polymerizes around the necks of budding vesicles and catalyzes membrane scission.

                Methods

                Enzymatic and turbidity assays are used in this study to monitor effects of Arc on dynamin activity and polymerization. Arc oligomerization is measured using a combination of approaches, including size exclusion chromatography, sedimentation analysis, dynamic light scattering, fluorescence correlation spectroscopy, and electron microscopy.

                Results

                We present evidence that bacterially-expressed His6-Arc facilitates the polymerization of dynamin 2 and stimulates its GTPase activity under physiologic conditions (37°C and 100mM NaCl). At lower ionic strength Arc also stabilizes pre-formed dynamin 2 polymers against GTP-dependent disassembly, thereby prolonging assembly-dependent GTP hydrolysis catalyzed by dynamin 2. Arc also increases the GTPase activity of dynamin 3, an isoform of implicated in dendrite remodeling, but does not affect the activity of dynamin 1, a neuron-specific isoform involved in synaptic vesicle recycling. We further show in this study that Arc (either His6-tagged or untagged) has a tendency to form large soluble oligomers, which may function as a scaffold for dynamin assembly and activation.

                Conclusions and general significance

                The ability of Arc to enhance dynamin polymerization and GTPase activation may provide a mechanism to explain Arc-mediated endocytosis of AMPA receptors and the accompanying effects on synaptic plasticity.
                  Cover page: Enhancement of dynamin polymerization and GTPase activity by Arc/Arg3.1
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2018)
                  Transected axons fail to regrow across anatomically complete spinal cord injuries (SCI) in adults. Diverse molecules can partially facilitate or attenuate axon growth during development or after injury1-3, but efficient reversal of this regrowth failure remains elusive4. Here we show that three factors that are essential for axon growth during development but are attenuated or lacking in adults-(i) neuron intrinsic growth capacity2,5-9, (ii) growth-supportive substrate10,11 and (iii) chemoattraction12,13-are all individually required and, in combination, are sufficient to stimulate robust axon regrowth across anatomically complete SCI lesions in adult rodents. We reactivated the growth capacity of mature descending propriospinal neurons with osteopontin, insulin-like growth factor 1 and ciliary-derived neurotrophic factor before SCI14,15; induced growth-supportive substrates with fibroblast growth factor 2 and epidermal growth factor; and chemoattracted propriospinal axons with glial-derived neurotrophic factor16,17 delivered via spatially and temporally controlled release from biomaterial depots18,19, placed sequentially after SCI. We show in both mice and rats that providing these three mechanisms in combination, but not individually, stimulated robust propriospinal axon regrowth through astrocyte scar borders and across lesion cores of non-neural tissue that was over 100-fold greater than controls. Stimulated, supported and chemoattracted propriospinal axons regrew a full spinal segment beyond lesion centres, passed well into spared neural tissue, formed terminal-like contacts exhibiting synaptic markers and conveyed a significant return of electrophysiological conduction capacity across lesions. Thus, overcoming the failure of axon regrowth across anatomically complete SCI lesions after maturity required the combined sequential reinstatement of several developmentally essential mechanisms that facilitate axon growth. These findings identify a mechanism-based biological repair strategy for complete SCI lesions that could be suitable to use with rehabilitation models designed to augment the functional recovery of remodelling circuits.
                    Cover page: Required growth facilitators propel axon regeneration across complete spinal cord injury.
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2018)
                    Transected axons fail to regrow across anatomically complete spinal cord injuries (SCI) in adults. Diverse molecules can partially facilitate or attenuate axon growth during development or after injury1-3, but efficient reversal of this regrowth failure remains elusive4. Here we show that three factors that are essential for axon growth during development but are attenuated or lacking in adults-(i) neuron intrinsic growth capacity2,5-9, (ii) growth-supportive substrate10,11 and (iii) chemoattraction12,13-are all individually required and, in combination, are sufficient to stimulate robust axon regrowth across anatomically complete SCI lesions in adult rodents. We reactivated the growth capacity of mature descending propriospinal neurons with osteopontin, insulin-like growth factor 1 and ciliary-derived neurotrophic factor before SCI14,15; induced growth-supportive substrates with fibroblast growth factor 2 and epidermal growth factor; and chemoattracted propriospinal axons with glial-derived neurotrophic factor16,17 delivered via spatially and temporally controlled release from biomaterial depots18,19, placed sequentially after SCI. We show in both mice and rats that providing these three mechanisms in combination, but not individually, stimulated robust propriospinal axon regrowth through astrocyte scar borders and across lesion cores of non-neural tissue that was over 100-fold greater than controls. Stimulated, supported and chemoattracted propriospinal axons regrew a full spinal segment beyond lesion centres, passed well into spared neural tissue, formed terminal-like contacts exhibiting synaptic markers and conveyed a significant return of electrophysiological conduction capacity across lesions. Thus, overcoming the failure of axon regrowth across anatomically complete SCI lesions after maturity required the combined sequential reinstatement of several developmentally essential mechanisms that facilitate axon growth. These findings identify a mechanism-based biological repair strategy for complete SCI lesions that could be suitable to use with rehabilitation models designed to augment the functional recovery of remodelling circuits.
                      Cover page: Required growth facilitators propel axon regeneration across complete spinal cord injury.
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