Honors Program

Honors in Biology

Date of Award

5-2022

Thesis Professor(s)

Lev Yampolsky

Thesis Professor Department

Biological Sciences

Thesis Reader(s)

Richard T. Carter, Dhirendra Kumar

Abstract

Hypoxia is a significant low oxygen state that has complex and diverse impacts on organisms. In aerobes, hypoxia causes numerous physiological changes and adaptive responses that vary depending on the level of oxygen depletion and on previous adaptation, hence its continued attention as an important abiotic stressor. Adaptive responses to hypoxia are primarily governed by the hypoxia-inducible-factors (HIFs), which activate downstream genetic pathways responsible for metabolic adjustments and homeostasis maintenance. In aquatic organisms, hypoxia is an important ecological constraint, as oxygen availability within waterbodies can vary greatly over time and space. Therefore, adaptation to hypoxia is likely pervasive, especially in genotypes originating from waterbodies prone to experiencing hypoxia. Here we report the transcriptional response to severe hypoxia in the freshwater crustacean Daphnia magna. We observe improved survival in media containing elevated calcium ion (Ca2+) concentrations. Additionally, we observe changes in lactate and pyruvate concentrations within tissues. To elucidate the transcriptome basis of these effects, we examine transcripts with known gene ontologies indicating roles in Ca2+ homeostasis and signaling, and in pyruvate metabolism, including gluconeogenesis (GNG). We observe the up-regulation of numerous transcripts encoding GNG pathway enzymes, including the rate-limiting enzyme phosphoenolpyruvate carboxykinase (PEPCK-C) and fructose-1,6-bisphosphatase (FBP). In contrast, no transcripts involved in Ca2+ homeostasis or signaling showed any significant differential expression. Many GNG transcripts are more up-regulated in clones from permanent waterbodies not prone to hypoxia, inconsistent with the hypothesis about its protective effects. One exception is the FBP transcript, identified to be up-regulated in some hypoxia-tolerant aquatic organisms.

Publisher

East Tennessee State University

Document Type

Honors Thesis - Open Access

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

Copyright

Copyright by the authors.

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