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    The Unexpected Role of Uric Acid in Lifecycle Synchronicity and Symbiosis

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    Jessica Menzies Thesis.pdf
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    Jessica Menzies Thesis
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    Type
    Thesis
    Authors
    Menzies, Jessica cc
    Advisors
    Aranda, Manuel cc
    Committee members
    Cui, Guoxin cc
    Peixoto, Raquel S cc
    Program
    Bioscience
    KAUST Department
    Biological and Environmental Science and Engineering (BESE) Division
    Date
    2021-07
    Embargo End Date
    2023-01-22
    Permanent link to this record
    http://hdl.handle.net/10754/670181
    
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    Access Restrictions
    At the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis will become available to the public after the expiration of the embargo on 2023-01-22.
    Abstract
    Functionality of Cnidarian symbiosis with Symbiodiniaceae is fundamental to reef ecosystem success. Symbiodiniaceae cells have a complex life history, which, in hospite, is controlled by the host. In addition to the endosymbiotic lifestyle, they can exist free-living cells which diurnally alternate between a coccoid, vegetative night-time form to a day-time motile, flagellated cell. Their cell division cycle is gated by external light cues, and correlates with transitions in cell morphology. In contrast, endosymbiotic cells have an elongated G1 phase – demonstrating a de-coupling of cell cycle from 24-hour cycle in response to symbiosis. Furthermore, daughters of dividing endosymbiotic Symbiodiniaceae remain as coccoid cells, de-coupling morphological and cell division cycles. How this occurs remains unknown. The answer may lie in crystalline uric acid deposits, which are present only in motile, daytime cells, correlating with G1 and S phase. These store excess nitrogen and are quickly metabolized in low nitrogen availability. They also function as an eyespot. The influence of uric acid on the life cycle of free-living and endosymbiotic Symbiodiniaceae is unknown. In this study, I treated cultures of B. minutum with allopurinol, an inhibitor of uric acid synthesis. Flow cytometry showed that allopurinol the reduced growth rate and ratio of coccoid:motile cell cultures. RNA sequencing and differential gene expression analysis identified biological processes enriched in allopurinol treatment. I hypothesize that an intracellular lack of nitrogen imposed lack of uric acid crystals stimulates the General Amino Acid Control pathway. This represses translation, explaining the downregulation of ribosomal proteins, and upregulates amino acid and purine de novo biosynthesis pathways. Repression of translation may slow cellular growth and the G1 phase of the cell cycle, reducing number of cells meeting the size threshold for G1/S transition. Without uric acid deposits, cells may lack a functioning eyespot and not receive light cues which usually trigger morphological transitioning. This may suppress the motile morphology of free-living Symbiodiniaceae and cells in hospite even though the cell division cycle progresses, albeit more slowly. Genes involved in biosynthesis of flagella, thecal plates and the eyespot are upregulated, suggesting suppression of the motile form may act downstream of transcription.
    Citation
    Menzies, J. (2021). The Unexpected Role of Uric Acid in Lifecycle Synchronicity and Symbiosis. KAUST Research Repository. https://doi.org/10.25781/KAUST-P0Y8O
    DOI
    10.25781/KAUST-P0Y8O
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-P0Y8O
    Scopus Count
    Collections
    Biological and Environmental Science and Engineering (BESE) Division; Bioscience Program; MS Theses

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