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Scholarly Works (2 results)

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UC San Diego Electronic Theses and Dissertations (2011)

Damage caused by lack of oxygen is a key factor in many serious disease states ranging from stroke and heart attack to asthma and high altitude mountain sickness. Determining the pathways that can ameliorate injuries caused by hypoxia is key to developing treatments and prevention of hypoxic damage. This dissertation examines the role of Notch signaling in potentiating Drosophila survival under chronic low oxygen conditions.

Pathway-level analysis of micro-array data of hypoxia-selected flies, the Notch signaling pathway was significantly up-regulated. Using the UAS-GAL4 system, the temporal and spatial specificity of Notch signaling was determined. The most robust results were found with glia-specific GAL4 drive, hence they were chosen for further characterization. Expression patterns of the GAL-4 glial drivers were confirmed by crossing them to a UAS-GFP transgenic fly line. Immunohistochemical analysis confirmed NICD (Notch Intracellular Domain) over-expression in glia cells. The developmental importance of Eaat1 glia was shown by crossing them to the UAS-reaper line; the results were embryonic lethal. Transcriptional up-regulation of Notch signaling was demonstrated by crossing flies stably over-expressing NICD with a reporter stock.

To address the question of what mechanism Notch utilizes to potentiate survival during hypoxia, several hypotheses were considered. First, Notch signaling may allow Eaat1-expressing glia to form a stem cell niche. This niche, in turn, allows the replacement of damaged/dead neurons injured during hypoxia.

Alternatively, other pathways may mediate the survival of these glial cells, which have been shown to be necessary to the survival of the whole organism. The metabolism of these glia could be altered via pyruvate dehydrogenase (PDH). Akt and NF-&kappaB are also known to interact with the Notch pathway. Perhaps canonical downstream target genes of Notch signaling, such as m-&alpha act as mechanism to allow survival of these crucial glia and thus the whole organism.

To study Notch interacting with other pathways, flies stably over-expressing NICD under the Eaat1 driver were crossed to UAS-RNAi flies targeting genes involved in pathways known to potentiate survival during hypoxia. Both Relish and m-&alpha act downstream of Notch signaling to mediate survival, demonstrating novel means of Notch up-regulation leading to hypoxic survival.

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Cover page: The Role of Notch in Survival During Chronic Hypoxia
  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2021)
Hypoxia is a critical pathological element in many human diseases, including ischemic stroke, myocardial infarction, and solid tumors. Of particular significance and interest of ours are the cellular and molecular mechanisms that underlie susceptibility or tolerance to low O2. Previous studies have demonstrated that Notch signaling pathway regulates hypoxia tolerance in both Drosophila melanogaster and humans. However, the mechanisms mediating Notch-conferred hypoxia tolerance are largely unknown. In this study, we delineate the evolutionarily conserved mechanisms underlying this hypoxia tolerant phenotype. We determined the role of a group of conserved genes that were obtained from a comparative genomic analysis of hypoxia-tolerant D.melanogaster populations and human highlanders living at the high-altitude regions of the world (Tibetans, Ethiopians, and Andeans). We developed a novel dual-UAS/Gal4 system that allows us to activate Notch signaling in the Eaat1-positive glial cells, which remarkably enhances hypoxia tolerance in D.melanogaster, and, simultaneously, knock down a candidate gene in the same set of glial cells. Using this system, we discovered that the interactions between Notch signaling and bnl (fibroblast growth factor), croc (forkhead transcription factor C), or Mkk4 (mitogen-activated protein kinase kinase 4) are important for hypoxia tolerance, at least in part, through regulating neuronal development and survival under hypoxic conditions. Becausethese genetic mechanisms are evolutionarily conserved, this group of genes may serve as novel targets for developing therapeutic strategies and have a strong potential to be translated to humans to treat/prevent hypoxia-related diseases.
    Cover page: Genetic interactions regulate hypoxia tolerance conferred by activating Notch in excitatory amino acid transporter 1-positive glial cells in Drosophila melanogaster
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