Carbonic anhydrase function and evolution in the respiratory gas exchange system of marine fishes

dc.contributor.advisorEsbaugh, Andrew
dc.contributor.committeeMemberThomas, Peter
dc.contributor.committeeMemberBrandl, Simon J
dc.contributor.committeeMemberBrauner, Colin J
dc.creatorDichiera, Angelina Maria
dc.creator.orcid0000-0002-9635-0229
dc.date.accessioned2022-09-26T22:19:58Z
dc.date.available2022-09-26T22:19:58Z
dc.date.created2021-08
dc.date.issued2021-08-15
dc.date.submittedAugust 2021
dc.date.updated2022-09-26T22:19:59Z
dc.description.abstractMany marine fishes have adaptive respiratory strategies to enable sufficient oxygen (O₂) uptake, as well as the excretion of metabolically-produced carbon dioxide (CO₂). A central figure in the intertwined systems of CO₂ excretion and tissue O₂ delivery is the metalloenzyme carbonic anhydrase (CA). In my dissertation I expand, and in some cases challenge, the classical role of CA in CO₂ excretion and its emerging role in tissue O₂ extraction in both the red blood cell (RBC) and tissue membranes. I investigated the role of RBC CA in a diverse group of fishes, and demonstrated basal fishes with a membrane-bound CA isoform in their gills (branchial CA-IV) possess a low-activity RBC CA. Using site-directed mutagenesis, I restored increased function to a basal fish RBC CA to demonstrate that a single amino acid is critical for CA function. Furthermore, phylogenetic analysis suggested high-activity RBC CA may have coevolved with enhanced hemoglobin (Hb) pH sensitivity in teleosts. I explored this relationship and demonstrated RBC CA activity dictated Hb-O₂ offloading rate in almost a 1:1 manner in red drum (Sciaenops ocellatus). RBC CA is best known for its role in CO₂ excretion so this study is the first to demonstrate RBC CA may be rate-limiting for O₂ offloading as well. An additional CA isoform has recently been implicated in tissue O₂ extraction: membrane-bound CA-IV found in the red muscle, heart, and eye. With the plethora of CA-IV isoforms that function in other physiological systems (e.g. acid-base and ion regulation), I sought to define which isoforms should be studied for respiration, using publicly available membrane-bound CA sequences for a comprehensive phylogeny, and paired with tissue distribution analyses. I demonstrated functional divergence in CA-IV isoforms in which some species possess multiple CA-IV isoforms for disparate physiological functions. This highlighted CA-IVa as the primary isoform to target for future respiratory gas exchange studies. Finally, I challenged fish with low O₂ exposure (hypoxia) to understand the role CA-IV may play under environmental stress, and in contribution to whole-animal performance. While fish did not recruit CA-IV under hypoxia acclimation as predicted, they maintained CA-IV protein synthesis to theoretically sustain tissue O₂ extraction. Furthermore, hypoxia acclimation improved swim performance under control conditions; however, anaerobic rather than aerobic processes seem to be driving this performance. Overall, my work presents critical information regarding the emerging roles of CA in tissue O₂ extraction in marine fishes, providing mechanistic and evolutionary insight on the enzyme’s function in respiratory gas exchange.
dc.description.departmentMarine Science
dc.format.mimetypeapplication/pdf
dc.identifier.urihttps://hdl.handle.net/2152/115935
dc.identifier.urihttp://dx.doi.org/10.26153/tsw/42832
dc.language.isoen
dc.subjectOxygen
dc.subjectCarbon dioxide
dc.subjectPhylogenetics
dc.subjectHypoxia
dc.subjectAcclimation
dc.titleCarbonic anhydrase function and evolution in the respiratory gas exchange system of marine fishes
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentMarine Science
thesis.degree.disciplineMarine science
thesis.degree.grantorThe University of Texas at Austin
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy
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