Grewal, Savraj S.Barretto, Elizabeth2020-12-222020-12-222020-12Barretto, E. (2020). FOXO as a regulator of hypoxia tolerance in Drosophila (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.http://hdl.handle.net/1880/112895Animals often live in conditions where environmental oxygen levels fluctuate. When oxygen is abundant, growth is promoted, but when oxygen is scarce, metabolic processes are altered to limit growth and promote survival. One important mechanism controlling responses in hypoxia is the regulation of metabolic gene expression. The conserved hypoxia-inducible factor (HIF) is a transcriptional regulator of genes important for hypoxia-responses. However, less is known about other transcription factors important in hypoxia adaptation. We have explored this question in Drosophila melanogaster. Drosophila can tolerate low oxygen conditions. At 5% oxygen, larvae slow their growth and development, but viability remains unaffected. At 1% oxygen, larvae and adults exhibit a state of ‘suspended animation’ but can survive for up to 12 or 30 hours respectively. We found that upon switching larvae from normoxia to hypoxia, the transcription factor Forkhead Box O (FOXO) was rapidly relocalized from the cytoplasm to the nucleus in larval tissues even though animals maintain normal feeding. Moreover, we saw that many known FOXO target genes were induced in animals exposed to hypoxia. FOXO is important for regulating starvation and stress responses and can regulate aging in Drosophila and Caenorhabditis elegans. We found that foxo null mutant larvae and adults show reduced survival in hypoxia. We also identified two downstream FOXO target genes involved in hypoxia tolerance. The first is the translational repressor 4e-bp. Upon exposure to hypoxia, 4e-bp expression is increased in a FOXO-dependent manner, while 4e-bp mutants showed a modest decrease in hypoxia survival. The second factor is the NF-kB transcription factor relish, a mediator of innate immune responses. We found that expression of relish and antimicrobial peptides was increased in a FOXO-dependent manner in hypoxia, and that relish null mutant animals have reduced survival in hypoxia. To better understand the breadth of FOXO responses, we examined metabolites and found that FOXO is necessary for maintenance of glycogen and lipid stores during hypoxia. foxo null mutants also have deregulated expression of lipases and glycolytic genes. Transcriptomic analyses further revealed that FOXO may modulate expression of genes involved in Notch and Hippo signaling, oocyte development, and translational effectors such as Ribosomal Proteins. Together, these data indicate that FOXO is a hypoxia-inducible factor that mediates tolerance to hypoxia by controlling protein synthesis, immune signaling, and metabolism.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.Education--SciencesAnimal PhysiologyBiology--CellGeneticsBiology--MolecularPhysiologyBiochemistrydoctoral thesis10.11575/PRISM/38489