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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2017)

Dust over the Atlantic undergoes decadal variability. Over the past three decades, satellite and in-situ measurements show a downward trend in dust concentration over the Atlantic, indicating there is less dust emission in the Sahara. Meanwhile, observations show an upward trend in the Sahel precipitation. However, it is unknown what affects dust emission in the Sahara and precipitation in the Sahel simultaneously. Dust emission in North Africa also undergoes synoptic variability and high concentration of dust is often observed in the western Sahara, but it is unclear whether dust over the western Sahara is due to local emission or dust transport from the east.

The aim of this thesis is twofold, first, to examine the role the Saharan heat low (SHL) plays in dust emission and precipitation from synoptic to decadal timescales. and second, to identify bias of dust in the model. To do so I use reanalysis and satellite products to construct the time series of dust, precipitation and the SHL and perform regression analysis to examine the effect of the SHL on precipitation and winds, which are associated with dust emission. Then I study the lead and lag relationship between the SHL and dust concentration in North African on the synoptic scale to identify source regions. Lastly, I identify the biases in a dust source function using dust output from a climate model.

The results from this thesis suggest that the warming of the SHL results in the increase of precipitation in the Sahel and the reduction in dust emission by changing low-level winds on the decadal timescale. On the synoptic scale, cool phases of the SHL is associated with more dust emission and 10% of the dust over western Africa is from source regions to the east. Lastly, the dust source function may overestimate dust emission in the Sahel and western Africa.

    Cover page: The Role the Saharan Heat Low Plays in the Variability of Dust Emission and Transport in North Africa from Synoptic to Decadal Scales
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2015)
    A large body of work has shown that year-to-year variations in North African dust emission are inversely proportional to previous-year monsoon rainfall in the Sahel, implying that African dust emission is highly sensitive to vegetation changes in this narrow transitional zone. However, such a theory is not supported by field observations or modeling studies, as both suggest that interannual variability in dust is due to changes in wind speeds over the major emitting regions, which lie to the north of the Sahelian vegetated zone. We reconcile this contradiction showing that interannual variability in Sahelian rainfall and surface wind speeds over the Sahara are the result of changes in lower tropospheric air temperatures over the Saharan heat low (SHL). As the SHL warms, an anomalous tropospheric circulation develops that reduces wind speeds over the Sahara and displaces the monsoonal rainfall northward, thus simultaneously increasing Sahelian rainfall and reducing dust emission from the major dust "hotspots" in the Sahara. Our results shed light on why climate models are, to date, unable to reproduce observed historical variability in dust emission and transport from this region.
      Cover page: On the decadal scale correlation between African dust and Sahel rainfall: The role of Saharan heat low–forced winds
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2022)
      Diabetic kidney disease (DKD), previously encountered predominantly in adult patients, is rapidly gaining center stage as a childhood morbidity and one that pediatric nephrologists are likely to encounter with increasing frequency. This is in large part due to the obesity epidemic and the consequent rise in type 2 diabetes in children and adolescents, as well as the more aggressive diabetes phenotype in today's youth with more rapid β-cell decline and faster development and progression of diabetes-related complications along with lower responsiveness to the treatments used in adults. DKD, an end-organ complication of diabetes, is at the very least a marker of, and more likely a predisposing factor for, the development of adverse cardiovascular outcomes and premature mortality in children with diabetes. On an optimistic note, several new therapeutic approaches are now available for the management of diabetes in adults, such as GLP1 receptor agonists, SGLT2 inhibitors, and DPP4 inhibitors, that have also been shown to have a favorable impact on cardiorenal outcomes. Also promising is the success of very low-energy diets in inducing remission of diabetes in adults. However, the addition of these pharmacological and dietary approaches to the management toolbox of diabetes and DKD in children and adolescents awaits thorough assessment of their safety and efficacy in this population. This review outlines the scope of diabetes and DKD, and new developments that may favorably impact the management of children and young adults with diabetes and DKD.
        Cover page: Diabetic kidney disease in children and adolescents: an update.
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2007)
        One mosquito opsin gene, NYD-OP7, has been cloned from Culex pipiens pallens. An open reading frame (ORF) of 1116 bp was found to encode a putative 371 amino acids protein which exhibits high identity with opsins from Aedes and Anopheles mosquitoes. Transcript expression of NYD-OP7 was determined by real-time PCR in all life stages of deltamethrin-susceptible and -resistant strains of the Culex mosquito. The results demonstrated that this gene is expressed at all developmental stages, and it is expressed predominantly at the pupae and adult stages. Meanwhile, in pupae and adults, NYD-OP7 is overexpressed in deltamethrin-resistant strain than in -susceptible strain. Importantly, stable expression of NYD-OP7 in the mosquito C6/36 cells can confer moderate deltamethrin resistance. Our study provides the first direct evidence that increased expression of an opsin gene may play some role in the development of deltamethrin resistance in Cx. pipiens pallens. © 2006 Elsevier Inc. All rights reserved.
          Cover page: Cloning and characterization of NYD-OP7, a novel deltamethrin resistance associated gene from Culex pipiens pallensCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2023)
          A T50I substitution in the K-Ras interswitch domain causes Noonan syndrome and emerged as a third-site mutation that restored the in vivo transforming activity and constitutive MAPK pathway activation by an attenuated KrasG12D,E37G oncogene in a mouse leukemia model. Biochemical and crystallographic data suggested that K-RasT50I increases MAPK signal output through a non-GTPase mechanism, potentially by promoting asymmetric Ras:Ras interactions between T50 and E162. We generated a switchable system in which K-Ras mutant proteins expressed at physiologic levels supplant the fms like tyrosine kinase 3 (FLT3) dependency of MOLM-13 leukemia cells lacking endogenous KRAS and used this system to interrogate single or compound G12D, T50I, D154Q, and E162L mutations. These studies support a key role for the asymmetric lateral assembly of K-Ras in a plasma membrane-distal orientation that promotes the formation of active Ras:Raf complexes in a membrane-proximal conformation. Disease-causing mutations such as T50I are a valuable starting point for illuminating normal Ras function, elucidating mechanisms of disease, and identifying potential therapeutic opportunities for Rasopathy disorders and cancer.
            Cover page: Structural and functional analyses of a germline KRAS T50I mutation provide insights into Raf activation.
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2015)
            Culex pipiens pallens is the most abundant Culex mosquito species in northern China and is an important vector of bancroftian filariasis and West Nile virus. Deltamethrin is an insecticide that is widely used for mosquito control, however resistance to this and other insecticides has become a major challenge in the control of vector-borne diseases that appear to be inherited quantitatively. Furthermore, the genetic basis of insecticide resistance remains poorly understood. In this study, quantitative trait loci (QTL) mapping of resistance to deltamethrin was conducted in F2 intercross segregation populations using bulked segregation analysis (BSA) and amplified fragment length polymorphism markers (AFLP) in Culex pipiens pallens. A genetic linkage map covering 381 cM was constructed and a total of seven QTL responsible for resistance to deltamethrin were detected by composite interval mapping (CIM), which explained 95% of the phenotypic variance. The major QTL in linkage group 2 accounted for 62% of the variance and is worthy of further study. 12 AFLP markers in the map were cloned and the genomic locations of these marker sequences were determined by applying the Basic Local Alignment Search Tool (BLAST) tool to the genome sequence of the closely related Culex quinquefasciatus. Our results suggest that resistance to deltamethrin is a quantitative trait under the control of a major QTL in Culex pipiens pallens. Cloning of related AFLP markers confirm the potential utility for anchoring the genetic map to the physical map. The results provide insight into the genetic architecture of the trait.
              Cover page: Identification of QTLs Conferring Resistance to Deltamethrin in Culex pipiens pallens
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2015)
              Current vector control programs are largely dependent on pyrethroids, which are the most commonly used and only insecticides recommended by the World Health Organization for insecticide-treated nets (ITNs). However, the rapid spread of pyrethroid resistance worldwide compromises the effectiveness of control programs and threatens public health. Since few new insecticide classes for vector control are anticipated, limiting the development of resistance is crucial for prolonging efficacy of pyrethroids. In this study, we exposed a field-collected population of Culex pipiens pallens to different insecticide selection intensities to dynamically monitor the development of resistance. Moreover, we detected kdr mutations and three detoxification enzyme activities in order to explore the evolutionary mechanism of pyrethroid resistance. Our results revealed that the level of pyrethroid resistance was proportional to the insecticide selection pressure. The kdr and metabolic resistance both contributed to pyrethroid resistance in the Cx. pipiens pallens populations, but they had different roles under different selection pressures. We have provided important evidence for better understanding of the development and mechanisms of pyrethroid resistance which may guide future insecticide use and vector management in order to avoid or delay resistance.
                Cover page: Development of Resistance to Pyrethroid in Culex pipiens pallens Population under Different Insecticide Selection Pressures
                • Article
                • Peer Reviewed
                ICTS Publications (2015)
                  Cover page: Development of Resistance to Pyrethroid in Culex pipiens pallens Population under Different Insecticide Selection PressuresCreative Commons 'BY' version 4.0 license
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