| Advisor : | DONG-ER ZHANG | ||
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| Abstract Title : | Functional Characterization of the Tumor Suppressor RASSF2 in t(8;21) Acute Myeloid Leukemia | ||
| Abstract : | Acute Myeloid Leukemia (AML) is a cancer of the myeloid blood cells, characterized by a sudden expansion of rapidly proliferating immature blood cells. The most common karyotypic abnormality associated with AML is a translocation between chromosomes 8 and 21, resulting in the formation of the AML1/RUNX1-ETO (AE) fusion protein. While this fusion protein severely disrupts hematopoiesis, it does not induce leukemia unless combined with other mutations. The specific mutations involved in leukemogenesis vary, but one mutation that is frequently observed is epigenetic silencing of the tumor suppressor, RASSF2. In fact, using a mouse model of t(8;21) AML, as well as publicly available gene expression datasets, we have identified RASSF2 as one of the genes that is the most significantly down-regulated in the presence of AE. Therefore, we hypothesize that down-regulation of RASSF2 by AE may be a critical step in the development of leukemia. One protein of the ten-member Ras-Association Domain Family (RASSF), RASSF2 contains several discrete domains whose structural and functional properties have been successfully outlined; however it has not been studied in the context of leukemia development. With this in mind, I hope to elucidate the role RASSF2 plays in t(8;21) AML by discovering which domains are necessary for its tumor suppressive function in the presence of the AE fusion protein. | ||
| Advisor : | JONATHAN LIN | ||
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| Abstract Title : | Mechanisms of Ubiquitylation and ER-Associated Degradation of P23H Mutant Rhodopsin in Retinal Degeneration | ||
| Abstract : | Rhodopsin protein is the archetypal G-protein coupled receptor that is specifically and massively expressed in rod photoreceptor cells. Over 200 rhodopsin mutations lead to inheritable retinal disease. The P23H point mutation in rhodopsin leads to autosomal dominant retinitis pigmentosa, in which progressive death of rod photoreceptor cells results in night blindness and eventual total retinal degeneration. Both in vitro and in vivo systems demonstrate that P23H rhodopsin is misfolded and subjected to depletion by endoplasmic-reticulum-associated degradation (ERAD). Proper expression of mature rhodopsin is important not only for rod functionality, but also for its viability. In line with this phenomenon, we have previously shown that P23H RHO homozygous mice demonstrate an early degradation of rhodopsin that precedes rod photoreceptor death. However, the specific genes that regulate rhodopsin degradation and post-translational modifications that target rhodopsin for degradation are poorly understood in the eye. In the classical ERAD pathway, lysine residues are conjugated to poly-ubiquitin signals (ubiquitylation) for degradation by the proteasome. Here, we mutated every lysine residue (11 total) of P23H rhodopsin to arginine to test which ones are important for ubiquitylation. Using transient transfection of these rhodopsin constructs in the HEK293 human cell line, we found that a P23H rhodopsin with all lysine residues mutated (K-null P23H) is much less ubiquitylated than P23H rhodopsin with lysine residues intact. Cyclohexamide blocking experiments demonstrate that the K-null P23H rhodopsin is more stable than P23H rhodopsin. Interestingly, rhodopsin constructs with singleton lysine mutations did not result in a significant change in ubiquitylation. In conclusion, ubiquitylation of multiple lysine sites on P23H rhodopsin may be involved in its ERAD processing. | ||
| Advisor : | DR. CHITRA MANDYAM | ||
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| Abstract Title : | Chronic administration of psychostimulants reduces hippocampal neurogenesis in young adult non human primates | ||
| Abstract : | Psychostimulants such as methamphetamine, MDMA, MDA have been used as treatment options for attention deficit disorders and narcolepsy; however, the vast majority of users take such amphetamines recreationally which eventually develops into addiction to these drugs. Pharmacodynamic studies show that chronic exposure to these drugs produces neurotoxicity which is evident as adverse affects on serotonergic and dopaminergic neurons in the limbic system of the brain, and these effects are hypothesized to promote and perpetuate addiction to the drugs. Though monoamine neurotoxicity as a function of cell death is valid for psychostimulant addiction, neurotoxicity by these drugs as a function of decreased neurogenesis in the dentate gyrus of hippocampus can be valid for relapse to psychostimulant addiction, as the hippocampus is important for relapse to drug seeking behaviors. In this context, only a small body of research has been devoted to understanding the effect of these drugs on neurogenesis in the hippocampus. Recent studies from others and our lab have found that both MDMA and methamphetamine significantly reduce levels of neurogenesis in the hippocampus of adult rodents. Furthermore, excessive psychostimulant intake-induced reduced levels of neurogenesis in the dentate gyrus of the hippocampus in adult rodents have been positively correlated with enhanced relapse to drug seeking behaviors. However, whether the detrimental effects of psychostimulants on developmental stages of neurogenesis are limited to rodent brain or occur in non human primates is unknown and was the focus of the current investigation. Our study investigated the levels of developmental stages of neurogenesis, cell death and the cell density of granule cell neurons after MDMA or MDMA in combination with MDA and methamphetamine exposure in young adult macaque monkeys in hopes to model the effects of these drugs on the young adult human hippocampus. Results from quantitative immunohistochemical analysis show that the two treatment conditions over 9.6 months causes > 80% decrease in the number of Ki-67 (neural progenitor) cells, and > 50% decrease in the number of Neuro D (immature neuron) cells, indicating a neurotoxic environment in the neurogenic niche in the hippocampus by MDMA alone or in combination with other amphetamines. Notably, the reduction in the number of newly born progenitors and neurons were not associated with changes in cell death (via apoptosis) or granule cell neuron numbers, indicating that psychostimulants selectively affected the generation and maturation of newly born granule cell neurons. In sum, our findings suggest that alterations in the cellular composition in the hippocampus during exposure to illicit drugs can promote maladaptive plasticity of hippocampal neurons during withdrawal, which may enhance relapse to drug seeking behaviors. | ||
| Advisor : | FRED H. GAGE | ||
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| Abstract Title : | A New Axonal Splice Variant of HDGF-related protein 3 Increases Mature Oligodendrocyte Numbers | ||
| Abstract : | In the central nervous system, axons are myelinated by oligodendrocytes (OLs). However, though our understanding of OL biology is increasing, the signals that emanate from the axons and modulate myelination are still poorly understood. Previous studies have found that HRP3-II, a newly identified isoform of the hepatoma-derived growth factor (HDGF) family, shows peak expression in the axons of spinal motor neurons before and during the myelination period. Furthermore, overexpression of HRP3-II increased Schwann cell proliferation and myelination, suggesting its importance for regulating the local pool of Schwann cells. Therefore, our goal is to determine whether HRP3-II also plays a critical role in regulating OLs in the central nervous system (CNS) using a recently developed CNS myelination model. The model is based on co-culturing mouse embryonic stem cell derived cortical neurons and OLs in microfluidic devices. We overexpressed HRP3-II in the neurons using a viral construct in the co-cultures. The average number of Myelin Basic Protein-positive OLs was significantly larger in the HRP3-II overexpressing co-cultures compared to controls; however, a similar increase was not seen on myelination in the HRP3-II overexpressing co-cultures, suggesting its role in the proliferation and/or maturation of OLs. | ||
| Advisor : | MAIKE SANDER | ||
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| Abstract Title : | Investigating a role for DNA damage response in the decline of beta cell growth after birth | ||
| Abstract : | Diabetes results from reduction in beta cell mass caused by immune assault or failure of the beta cells to adapt to increased needs of insulin. There is evidence that patients with both type I and type II diabetes still harbor functional beta cells in the pancreas, suggesting that expanding these cells could improve blood glucose homeostasis in patients. However, strategies to expand residual functional beta cells are still lacking. This is due to the poor understanding of how beta cells normally regulate their capacity to replicate and expand. Studies have shown that beta cells lose their ability to proliferate with age, with the most dramatic decline in beta cell proliferation observed immediately after birth; however the reason for this early, rapid decline is still unclear. Our lab has shown that activation of a DNA damage response (DDR) in beta cells coincides with the decline in beta cell proliferation occurring during the postnatal period. The mIns1-H2b-mCherry transgenic reporter mice, which mark all beta cells by nuclear mCherry expression, were used to analyze the expression of markers of DNA damage, including 53BP1 and γH2AX at postnatal day 1 (P1) and P21. We observed an age-dependent increase of expression of these DNA damage markers. Additional DNA damage markers were used to observe the DDR in P1 and P21 mice. To directly evaluate and quantify DNA damage in postnatal beta cells, we are using single-cell gel electrophoresis (alkaline comet assay) to measure DNA strand breaks in beta cells. Islets isolated from P1 and P21 mcherry reporter mice were dissociated to single cells. FACs was utilized to isolate the beta cells and alkaline comet assays were performed to detect single and double-strand breaks, as well as base modifications. These experiments help confirm the occurrence of genotoxic stress that induces cell cycle arrest in postnatal beta cells. | ||
| Advisor : | MELANIE GAREAU | ||
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| Abstract Title : | Administration of probiotics normalizes deficits in the microbiota-gut-brain axis induced by DSS-colitis | ||
| Abstract : | Altered behavior and mood disorders, including anxiety, depression and cognitive dysfunction, occur in the context of intestinal diseases such as inflammatory bowel disease (IBD) and affect patient quality of life. Our aim was to determine whether colonic inflammation precipitates behavioral defects and whether these changes can be ameliorated by probiotics. Dextran sodium sulfate (DSS) was administered to 6-7 week old C57BL/6 mice via drinking water for 5 days followed by either 3 days (8 d post-DSS) or 9 days (14 d post-DSS) of normal drinking water. A subset of mice was given probiotics (Lactobacillus rhamnosus [R0011] and L. helveticus [R0052]; 109 CFU/ml orally) starting 7 days prior to DSS and continuing until the end of the experiment. Changes in weight, colon length, behavior and microbiota were assessed. At 8 d post-DSS, weight loss and colonic shortening (both p<0.01) were observed, indicating colonic disease. Dysbiosis was also observed. DSS mice (vs. controls) demonstrated impairments in recognition memory (p<0.01) and the presence of anxiety-like behavior (p<0.05), which were both resolved by 14 d post-DSS. Probiotics ameliorated colonic disease (p<0.05) and defects in behavior (p<0.05), and partially restored the microbiota. Taken together, these findings indicate the presence of dysregulation of the microbiota-gut-brain axis in the setting of DSS-induced colitis that can be prevented by treatment with probiotics. | ||
| Advisor : | CAROLYN KURLE | ||
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| Abstract Title : | Vibrissae growth rates and foraging and migration patterns for juvenile male northern fur seals (Callorhinus ursinus) from St. Paul Island, Alaska using stable isotope analysis | ||
| Abstract : | Populations of northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Alaska have experienced an unexplained decline since the mid-1970s. Understanding migratory and foraging ecology patterns of northern fur seals would contribute to understanding their declines and would contribute to better management of their population. A method used to reconstruct marine vertebrate foraging and movement patterns is stable isotope analysis of animal tissues. Vibrissae in Otariidae grow continuously throughout their lives beginning in utero, thereby incrementally accumulating stable isotope data that reflect their food sources and migratory patterns from before birth to the time of vibrissae collection. We analyzed the stable isotope values at intervals along entire vibrissae collected from 8, known age (2, 3, and 4 years), juvenile male northern fur seals from St. Paul Island, Alaska. This provided us with stable isotope values along a temporal scale from embryogenesis to whisker collection in August of 2014. We determined vibrissae growth rates to match stable isotope patterns to specific time periods in the animals' lives. In addition, we analyzed the stable isotope values of the segments from the longest and shorter vibrissae from the same animals to determine if equivalent data were reflected in both sizes. This could allow for fewer analyses per whisker, saving resources. We found annual oscillations in the δ13C and δ15N values, indicating that juvenile male fur seals are regularly foraging at some distance away from the Pribilof Islands during the non-breeding season and returning every year to the Pribilof Islands. Average vibrissae growth rate per month for juvenile males (2.11 mm/month ± 0.58 mm) had a fairly high standard deviation and the δ13C oscillations seem to provide a more accurate representation of variations in foraging location over time than the δ15N values. This was expected as δ13C values more accurately reflect foraging location. Comparisons of isotope data from different sized vibrissae, as well as determining more exact interpretations of foraging and migratory patterns, are in progress. | ||
| Advisor : | DR. KAREN PIERCE | ||
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| Abstract Title : | The Genetics of Language and Social Behavior in Autism | ||
| Abstract : | Autism, a neurodevelopmental disorder marked with difficulties in one's language ability and social behavior, is currently diagnosed through behavioral analyses diagnostics such as the Autism Diagnostic Observations Schedule. While these types of diagnostics have been reported to be effective, these tests are likely to miss children whom do not demonstrate the stereotypical behaviors of a typical autistic individual like restricted and repetitive behaviors. These children will appear to be typically developing until a certain point in their lives, which follow a decline or slower development of skills. Given current research regarding the genetics of autism, I investigated whether genetic variation in autistic children compared to typically developing children could be further stratified to an autistic child's language ability and social behavior. Analyzing both copy number variations and gene expression in autistic children and typically developing children, my results support previous studies in detecting genetic differences (variation) between the two groups. Moreover, my findings suggest that there may be group differences in biological networks related to CNVs and differentially expressed genes in autistic children with poor versus good language ability and poor versus good social behavior. Genetic variation in children with poor language ability and poor social behavior is closely associated with biological networks related to neuronal development, cytoskeleton, and cell adhesion. In children with better language ability and better social behavior, there is a larger presence of networks associated with immune response and inflammation in addition to the biological networks found in poor language and poor social behavior groups. These findings demonstrate the potential of a biologically based marker for earlier detection of autism risk as well as an indicator for areas of difficulty in the child?s development. | ||
| Advisor : | DR. MAIKE SANDER, M.D. | ||
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| Abstract Title : | Regulation of cell fate specification in hESC-derived pancreatic cell types. | ||
| Abstract : | During pancreas development, undifferentiated cells must undergo stepwise progression toward particular cell fates. The emergence of the distinct cell types of the pancreas relies on the capacity of lineage intermediates to properly interpret and respond to environmental inductive cues, an ability termed developmental competence. Enhancers have been shown to be critical in spatiotemporal gene regulation during development. However, how enhancers acquire the ability to translate signals from the extracellular environment into cell-type-specific transcriptional responses during development is poorly understood. Epigenetic priming and activation of enhancers by the pioneer transcription factors FOXA1 and FOXA2 has been proposed to confer developmental competence in various stages of pancreas lineage specification. We have been able to show that enhancers are first recognized by the pioneer transcription factors FOXA1 and FOXA2 when competence is acquired, while subsequent recruitment of lineage-inductive transcription factors, such as PDX1, leads to enhancer and target gene activation. Using differentiation of human embryonic stem cells (hESCs) as a model for pancreas development, we employed qRT-PCR, ChIP-qPCR, and ChIP-seq to elucidate the role and requirement of FOXA1, FOXA2 and PDX1 in pancreas differentiation. We also examined genome-wide changes in chromatin modifications at various stages of pancreas differentiation to assess the activity of enhancers that are relevant to pancreas development. Together, these studies will help uncover principles by which cells acquire competence to respond to lineage-inductive signals during development. | ||
| Advisor : | ERIC ZORRILLA | ||
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| Abstract Title : | TRH-DE Knock Out Mice Display an Anti-depressant- but Not Anxiolytic-like Phenotype | ||
| Abstract : | Thyrotropin-releasing hormone-degrading ectoenzyme (TRH-DE) hydrolyzes released thyrotropin-releasing hormone (TRH), limiting TRH action. Studies suggest that TRH exerts anxiolytic- and antidepressant-like actions, and TRH-DE is highly expressed in brain regions that subserve emotional behavior. The present studies tested the hypothesis that reducing TRH-DE function by targeted gene knockout would have anxiolytic- or antidepressant-like activity. Adult female and male mice of wild-type (C57BL/6J background; n=25), heterozygous (n=27), and TRH-DE knock out (n=14) genotypes were exposed to Elevated Plus Maze (EPM), Light-Dark box (LD), and Forced Swim (FST) behavioral tests. Videotaped behavior was scored naive to genotype and analyzed by ANOVA. Adult female and male mice of WT (n=16) and TRH-DE KO genotypes (n=16) were then compared for operant self-administration of food+water and a sucrose (3%)-saccharin(0.125%) solution. The time spent in the open arm and light box for EPM and LD, respectively, did not differ by genotype. A main effect of Genotype was observed for forced swim immobility (F(2,60)=4.36,p<0.02), whereby KO (p=0.01) and heterozygote (p=0.02) mice were significantly less immobile than WT littermates. A main effect of Sex for climbing reflected that males climbed more than females (F(1,60)=8.926,p<0.005). Sex x Genotype interactions reflected that male, but not female, TRH-DE KO mice self-administered more food and water than WT controls following acquisition. Knocking out TRH-DE function had an antidepressant-like effect in the FST, but did not show an anxiolytic-like effect or impair learning and memory in self-administration testing. | ||
| Advisor : | MICHAEL DAVID | ||
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| Abstract Title : | The Characterization of Schlafen11's Ability to Inhibit HIV Viral Synthesis | ||
| Abstract : | Our innate immune system employs several defense mechanisms against invading pathogens. Once detected, immune cells secrete messenger proteins (cytokines) to signal the invader's presence. Upon Human Immunodeficiency Virus (HIV) infection, dendritic cells release a specific type of cytokine known as interferon-1 (IFN-1) , which activate interferon-stimulated early response genes (ISGs). Schlafen (SLFN) is part of a family of mammalian ISGs that are induced by pathogens that activate the interferon regulatory 3 (IRF3) pathway. It has been shown that SLFN11, a human isoform of SLFN, disrupts HIV viral protein synthesis by exploiting HIV's use of low-abundance tRNAs. The regulation of ISGs such as SLFN11 are not well understood; therefore, I propose several regulatory sites of SLFN11 that are necessary for its function of inhibiting HIV viral synthesis in vitro. I also propose that DNA-dependent Protein Kinase (DNAPK) is a positive regulator of SLFN11. Furthermore, my studies suggest that a single nucleotide polymorphism (SNP) of SLFN11 could be contributing to the HIV/AIDS epidemic in Sub-Saharan Africa. | ||
| Advisor : | NICOLE PURCELL | ||
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| Abstract Title : | Physiological activation of Akt by PHLPP1 deletion protects against pathological hypertrophy | ||
| Abstract : | The serine/threonine kinase Akt is involved in many cellular processes including growth, survival, metabolism, protein synthesis, and angiogenesis. In particular, the activation of Akt induces cardiac hypertrophy, a process in which the heart undergoes cell enlargement in order to increase or maintain cardiac function. Akt activation causes physiological hypertrophy whereas prolonged Akt activation contributes to pathological hypertrophy and the development of heart failure. Extensive research has focused on regulating Akt activation; however, the mechanism of inactivation by phosphatases is largely unknown. A newly discovered phosphatase, PHLPP1 (PH domain leucine-rich repeat protein phosphatase) was found to dephosphorylate Akt. To determine the effect of PHLPP1 removal in the heart, we used global PHLPP1 knockout (KO) mice. At baseline, wild-type (WT) and PHLPP1 KO exhibit no differences in heart size up to one year of age. However, PHLPP1 deletion increased Akt activity in the heart and cardiomyocytes. In a model for exercise-induced hypertrophy, PHLPP1 removal resulted in increased heart size and myocyte cell area compared to WT. In contrast, in a model of pathological hypertrophy induced by transverse aortic constriction (TAC), compared to WT, PHLPP1 KO exhibited an attenuated increase in heart size, myocyte cell area, hypertrophic gene expression, fibrosis, and cell death. Furthermore, KO mice had a sustained increase in angiogenic marker expression and capillary density compared to WT. We demonstrate that removal of PHLPP1, which increases Akt activity in the heart to physiological levels without affecting cell size, increases angiogenesis and attenuates pathological hypertrophy following TAC. | ||
| Advisor : | DAVID A. HOLWAY | ||
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| Abstract Title : | The effects of removing an introduced pollinator on the reproductive success of California native clustered tarweed | ||
| Abstract : | My project investigates the reproductive effect of removing pollination services by honey bees (Apis mellifera) from California native plants. An exotic species introduced to California less than two hundred years ago, they provide crucial pollination services for human agriculture and horticulture. Honey bees living in feral colonies are widespread in southern California, making up 85 to 95 percent of floral visits to certain native plant species. But very little research has been done to assess the ecological impact of this non-native pollinator. Honey bees, while highly efficient at collecting pollen and nectar for their own purposes, have a less clear relationship with the native plants they visit. Introduced bee species can interact with native communities in unpredictable ways: they can act as nectar robbers, their visits can vary in efficiency and frequency, and they often compete with native bees for floral resources. I plan to discover the effect that experimental honey bee removal has on reproduction of a California native plant, clustered tarweed (Deinandra fasciculata), through the lens of California's severe drought. In a landscape of declining native bee diversity and abundance, can floral visits from Apis mellifera serve as "emergency pollination" for threatened coastal plant communities? | ||
| Advisor : | DAVID TRAVER | ||
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| Abstract Title : | Molecular Mechanisms of GATA2 in HSC Development | ||
| Abstract : | Treatment of hematological diseases such as leukemia and lymphoma is dependent on transplantation of hematopoietic stem cells (HSCs) derived from limited numbers of immune-compatible donors. Recent advances in stem-cell biology have enabled the generation of pluripotent stem cells (iPSCs) from terminally differentiated cells of healthy patient tissue. This would circumvent the current limitation of transplantation therapies; however, inadequate knowledge of the innate molecular mechanisms hinders progress toward this end. A key hematopoietic regulator in mammals, GATA2, functions to specify both endothelial and hematopoietic cell differentiation. A recent study in zebrafish has identified a paralog, gata2b, retaining the hematopoietic functions of GATA2. Coupled with gata2a, which retains the endothelial functions of GATA2, we have dissected the molecular mechanisms of GATA2 to gain novel insights into the formation of HSCs. | ||
| Advisor : | JENS LYKKE-ANDERSEN | ||
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| Abstract Title : | Characterizing the interaction between the translational repressor complex 4EHP-GYF2 and the ARE-binding protein TTP | ||
| Abstract : | Precise control of gene expression involves multiple steps beyond transcription, including mRNA turnover and translational repression. One pathway in particular involves the RNA-binding protein tristetraprolin (TTP), which binds to AU-rich elements (AREs) in the 3? untranslated region of proinflammatory- and cancer-associated mRNAs and promotes their decay by recruiting degradation factors. Though TTP is well known to be involved in mRNA decay, its role in translational repression is poorly understood. Recently, the Lykke-Andersen lab (by mass spectrometry in collaboration with the Bennett Lab) revealed a novel interaction between TTP and the translational repressor complex 4EHP-GYF2. This finding also suggests TTP-mediated mRNA decay and translational repression could be interdependent. To better understand the functional implications of this novel interaction between TTP and 4EHP-GYF2, first the domains of TTP needed for binding GYF2 and 4EHP were mapped out by mutagenesis of TTP in 293T cells. Co-immunoprecipitation of WT and deletion mutants of TTP revealed the N-terminal domain of TTP to be sufficient and necessary for binding to the 4EHP-GYF2 complex, whereas the C-terminal domain and RNA-binding domain were not. Further mapping of TTP revealed conserved PPPPG motifs, that when mutated, results in almost complete loss of binding to the 4EHP-GYF2 complex. We further tested for the direct protein-protein interaction by in vitro pull-down experiments using recombinant TTP, 4EHP, and GYF2, which revealed weak binding of 4EHP to TTP, but an enrichment for binding upon the addition of GYF2, indicating GYF2 is important in forming this complex. We are currently studying the functional implication of these interactions by in vitro translation experiments, in which we?re measuring the luciferase activity of an ARE-containing reporter RNA after the addition of different combinations of recombinant TTP, 4EHP, and GYF2, in order to test whether TTP can mediate translational repression via its interaction with 4EHP-GYF2 in vitro. | ||
| Advisor : | JENNIFER SMITH | ||
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| Abstract Title : | Abundance and spatial distribution of juvenile corals on Palmyra Atoll | ||
| Abstract : | Scleractinian corals are fundamental to structuring coral reef ecosystems, however the processes that drive their abundance and spatial distribution are largely unknown. Using photomosaic images created by stitching together thousands of individual images, we can expand our view of the reef from 1 m2 quadrats to 100 m2 plots of the benthic habitat, allowing the opportunity for new spatial analyses to be conducted on these reef systems. This study uses mosaics from Palmyra Atoll located in the Central Pacific, which due to its remote location and restricted human presence provides insight as to how these systems operate under little to no anthropogenic influence. Specifically we will look at the early life stages of corals, or juveniles (<5 cm diameter) in order to determine how settlement preferences or reproductive strategies are influencing the spatial distribution of different species. In addition, by comparing the juvenile distributions to adult distributions, we can understand what the influence of choices made during the early life stages has on the distribution of corals in relation to competition forces acting on these long-lived adult populations. | ||
| Advisor : | JACK D. BUI, MD, PHD | ||
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| Abstract Title : | Heterologous Cell-Cell Fusion Promotes Chemoresistance in Cancer | ||
| Abstract : | Cancer relapse is the leading cause of mortality among cancer patients. Despite positive prognosis of complete remission following conventional treatment regimes, cancer can return in more aggressive manners with increased metastatic potential and resistance to chemotherapy. Repeated observations of giant multinucleated cells in cancer biopsies suggest the existence of hybrid cells derived from cell fusion. However, the physiological significance of cell fusion in the context of cancer remains largely unexplored. Several studies have shown that cell fusion can increase the metastatic potential of cancer cells and increase resistance to chemotherapy by increasing the genetic (and subsequent phenotypic) diversity of hybrid cells and their progeny. However, these studies relied on artificially induced fusion methods, and therefore may not reflect true physiology. We recently developed a model system to study spontaneous cell-cell fusion in the context of cancer. Using a Cre-lox reporter system, we observed spontaneous cell fusion events occur both in vitro and in vivo. We used this model system to test whether cell-cell fusion could augment chemoresistance in two different cancer models. Here we show that fusion between cancer cells and fibroblasts promotes resistance against two chemotherapy drugs in B16 melanoma and fibrosarcoma. In addition, we found that in vivo derived B16 hybrids are more resistant to chemotherapy than parental B16 melanoma cells. These findings suggest that spontaneous cell-cell fusion could be a potential mechanism by which cancer evades chemotherapeutic treatment. | ||
| Advisor : | MELANIE GAREAU, KIM BARRETT | ||
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| Abstract Title : | Nod1/Nod2 Receptors Modulate the Microbiota-Gut-Brain Axis | ||
| Abstract : | The association between intestinal diseases, mood disorders and cognitive deficits is increasingly recognized. Previous studies from our lab suggest that chronic intestinal diseases, such as infection with an enteric pathogen, in combination with an acute psychological stressor (water avoidance stress [WAS]), can induce anxiety-like behavior and memory defects in mice. In our current study, we hypothesized that nucleotide binding oligomerization domain (Nod) receptors, as important modulators of homeostasis between the host immune system and the gut microbiota, are integral regulators of the microbiota-gut-brain axis. Using Nod1/Nod2 double knockout (NodDKO) mice, we performed behavioral testing, qPCR analysis of stool bacterial DNA, and serum corticosterone analysis. Compared to wild type (WT) controls (C57BL/6), NodDKO mice displayed anxiety-like behaviors (light/dark box test, p<0.001) and deficits in recognition memory (novel object recognition [NOR] test, p<0.001) following exposure to a single session of WAS. WT and NodDKO mice differed in the composition of their microbiota in 4 of 7 bacterial groups studied by qPCR, indicating the presence of intestinal dysbiosis in NodDKO mice. WAS-induced elevated levels of serum corticosterone were also observed in NodDKO mice. To evaluate a potential role for the microbiota in mediating these effects, given the presence of dysbiosis in NodDKO mice, WT and NodDKO mice were co-housed at weaning and behavior assessed in adulthood. Co-housing confirmed that Nod1/Nod2 receptors are important for recognition memory and anxiety-like behavior, with defects remaining despite microbiota normalization. Interestingly, co-housing also ameliorated the WAS-induced spike in corticosterone levels in co-housed WT and NodDKO mice. Therefore, our study indicates that Nod receptors serve as key signaling molecules, potentially acting via the hypothalamic pituitary adrenal (HPA) axis, to modulate the microbiota-gut-brain axis in mice. | ||
| Advisor : | DANIEL GIBBS | ||
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| Abstract Title : | Generating inducible neurotrophic gradients in SCI using pharmacogenetics | ||
| Abstract : | Brain derived neurotrophic factor (BDNF) is a potent and multifunctional neurotrophin in both central and peripheral nervous systems; promoting neuronal survival and synaptic plasticity, as well as stimulating axonal regeneration and guidance following injury. In models of spinal cord injury, delivery of BDNF has demonstrated great promise for promoting neuronal survival as well as enhancing axonal regeneration, plasticity and re-myelination (reviewed in Weishaupt, Blesch and Fouad, Exp. Neurol. 2012). However, constitutive delivery of BDNF without regulated spatial and temporal control of expression levels and duration can have significant adverse side effects. These include spasticity, aberrant plasticity and increased neuropathic pain. In this study, we describe a novel approach to develop an AAV-based viral vector platform that provides drug dependent control of endogenous BDNF expression in a rat model of SCI. We demonstrate that AAV2-mediated expression of the rM3Ds GaS-coupled Designer Receptor Exclusively Activated by Designer Drugs (Gs-DREADD) can significantly increase endogenous BDNF expression in vitro and in vivo, in a spatially and temporally restricted manner. Gs-DREADD is a synthetic GPCR engineered to be activated exclusively by clozapine -N-oxide (CNO), leading to elevated intracellular cAMP. Intra-peritoneal delivery of CNO four weeks post AAV2 administration to C7/8 grey matter significantly increased endogenous BDNF production in vivo in AAV2-GsDREADD treated animals as compared to control animals. Following a single IP administration of CNO, BDNF levels peaked at 24 hours post delivery, and expression was spatially restricted to the injection site. We present additional data describing the time course of Gs-DREADD dependent BDNF expression in response to CNO. Future studies will assess the effect of AAV2-Gs-DREADD mediated control of endogenous BDNF expression on axon regeneration and targeting when combined with neural stem cell grafts in a rat cervical dorsal column lesion model of SCI. | ||
| Advisor : | SUSAN GOLDEN | ||
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| Abstract Title : | Prophage Controls Biofilm Formation and Photosynthesis in the cyanobacterium Synechococcus elongatus PCC7942 | ||
| Abstract : | Biofilms are surface-associated bacterial communities embedded within self-produced extracellular polymeric substances. Understanding mechanisms regulating biofilm formation in photosynthetic cyanobacteria will enable improvements in the harvesting, dewatering, and protecting of biomass for production of renewable bioproducts including biofuels. We identified a complete prophage integrated into the genome of the cyanobacterium Synechococcus elongatus PCC 7942 that represses biofilm formation and modulates photosystem concentrations. Genetic removal of the prophage or specific prophage genes from the host?s genome causes cells to form biofilms and increase photosystem production. This implies that, in natural environments, the prophage controls the ecological niche of the cyanobacteria and provides a new technology for controlling phenotypes that enhance industrial production of bioproducts. | ||
| Advisor : | JOSHUA KOHN | ||
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| Abstract Title : | Long-term effects of beach nourishment on intertidal invertebrates | ||
| Abstract : | Although beach nourishment is becoming an increasingly popular means to remediate coastal erosion, no consensus exists regarding how long the addition of sand to eroded beaches will affect intertidal invertebrates, key components of sandy beach ecosystems. We monitored the intertidal invertebrate community for fifteen months following a nourishment project at eight beaches across San Diego County. Nearly all taxa showed major declines in abundance immediately following nourishment. While some invertebrates recovered within the year, the polychaete community, consisting of Scolelepis spp. and several other numerically important taxa, showed a strong nourishment-induced reduction in abundance that persisted through the end of the study. The large negative effect of nourishment on polychaetes, coupled with their overall importance to the invertebrate community, resulted in a more than twofold reduction in overall invertebrate abundance on nourished beaches at 15 months. Such reductions may have far reaching consequences for sandy beach ecosystems, as community declines can reduce prey availability for shorebirds and fish. As this and other recent studies have revealed longer times for the recovery of intertidal invertebrates than previously observed, more cautious estimates regarding the magnitude and duration of impacts of beach nourishment should be applied to management practices. | ||
| Advisor : | JOAN HELLER BROWN | ||
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| Abstract Title : | Selective coupling of the S1P3 receptor subtype to S1P-mediated RhoA activation and cardioprotection | ||
| Abstract : | Sphingosine-1-phoshpate (S1P) is a bioactive lysophospholipid that signals through a variety of G-protein coupled receptor subtypes. S1P is generated and released at sites of tissue injury and acts on three major subtypes, S1P1, S1P2, and S1P3, to mediate cardiovascular responses. We previously demonstrated that S1P confers cardioprotection against ischemia/reperfusion and that S1P activates RhoA and its downstream effector PKD1 to lead to cardioprotection. Which S1P receptor subtype is responsible for these responses has not been determined. We knocked down the three major S1P receptors using siRNA and assayed for RhoA activation induced by S1P in neonatal rat ventricular myocytes (NRVMs). Knockdown of S1P3 ¬¬markedly reduced RhoA activation and subsequent phosphorylation of PKD1 while knockdown of S1P1 and S1P2 did not. Using siRNA or pertussis toxin to inhibit different G-proteins, we further established that S1P regulates RhoA activation through Gα13, but not Gα12, Gαq, or Gαi. To investigate the role of S1P3 receptors in the adult heart, we subjected hearts isolated from wild-type (WT) or S1P3 knockout (KO) mice to ex vivo ischemia/reperfusion in the Langendorff mode. Addition of S1P prior to ischemia/reperfusion reduced infarct size by 31% in WT hearts but this protection was abolished in the S1P3 KO mouse heart. To further confirm the role of S1P3 in cardioprotection we perfused WT mouse hearts with a S1P3-specific agonist CYM-51736. Infarct development was attenuated to a similar degree as that observed with nonselective S1P receptor subtype activation. Our findings reveal that the actions of S1P on the S1P3 receptor and its coupling to Gα13 to activate RhoA are responsible for cardioprotection against ischemia/reperfusion. Accordingly, specific drug targeting of S1P3 receptors could provide therapeutic benefits in ischemic heart disease without the undesirable effects of global activation of other cardiac S1P receptors. | ||