Date of Graduation

8-2022

Document Type

Thesis

Degree Name

Master of Science in Cell & Molecular Biology (MS)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Tipsmark, Christian K.

Committee Member

Pinto, Ines

Second Committee Member

Greene, Nicholas P.

Keywords

Claudins; Euryhaline; Gill; Killifish; Opercular membrane; Osmoregulation

Abstract

Atlantic killifish (Fundulus heteroclitus) are euryhaline teleosts, which means they can thrive in environments with varying salinities, ranging from concentrated seawater (SW) to dilute fresh water (FW) and thus survive in estuaries. To be able to maintain ionic and osmotic homeostasis in these diverse salinities, osmoregulatory organs like gill and opercular membrane must be able to adjust the permeability and transport of water and ions. The surface epithelia in these organs need to prevent the passive flux of ions and water in a drastically changing environment, while being able to switch between active ion secretion or uptake dependent upon environmental salinity. The tight junctions between the epithelial cells are critical to this phenotypic plasticity. The claudin (Cldn) proteins define tight junction permeability and molecular variants predicted to be important in gill and opercular membranes (cldn30c, cldn32a, cldn10c, cldn10d, cldn10e, cldn10f) are the focus of this thesis. The studies tested the organs distribution of these cldns and examined their regulation in gill and opercular membranes by salinity, prolactin, and cortisol. Analysis of the organ distribution largely confirmed that they are highly expressed in gill and opercular membranes when compared with muscle, liver, intestine, kidney and brain. While salinity acclimation generally did not affect mRNA levels, Cldn30c protein expression was elevated in FW compared to SW. Hormone ex vivo gill explant experiments showed that the FW hormone prolactin specifically stimulated cldn30c and cldn32a , both hypothesized to be critical to salt retention in freshwater. In contrast, cortisol affected cldn10c and cldn10f with a putative role in salt secretion in seawater. The thesis demonstrated the specific hormonal control of cldns and the significance of post-translational mechanisms was emphasized by the difference in salinity induced Cldn30c mRNA and protein levels.

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