Date of Award
Robert M. Dores
Cartilaginous fish, MC2R, MRAP1, MRAP2, Whale shark
Among bony vertebrates, the melanocortin-2 receptor ortholog is unique among the family of five melanocortin receptors on the basis that it is dependent on its accessory protein, MRAP1, for trafficking and activation, and is selective for activation by ACTH alone. Previous studies on the MC2R orthologs of select cartilaginous fish, the elephant shark (Callorhinchus milii) and the red stingray (Dasyatis akajei), revealed divergent traits in a less obligatory relationship on MRAP1 and its ability to be activated by ACTH or the MSH-sized peptides. However, observed traits were not consistent between these two cartilaginous fish species, posing the question as to whether there is another divergence of traits between subclasses of cartilaginous fish. Nascent availability of another cartilaginous fish genome, that of the whale shark (Rhincodon typus), provided the opportunity for classification of another cartilaginous fish MC2R ortholog. This new information allowed for the possibility of more thoroughly determining the phylogeny of MC2R traits in vertebrates. Initial characterization of the wsMC2R ortholog showed that it was able to be activated by either ACTH or the MSH-sized peptides. While this ortholog did not show a full dependence on MRAP1 for basal function, co-expression of wsMRAP1 or wsMRAP2 improved function overall. Analysis of the activation mechanism of the wsMC2R ortholog suggested a hybrid mechanism between the proposed one-step activation mechanism for the elephant shark MC2R ortholog and the proposed two-step activation mechanism for the bony vertebrate MC2R orthologs. In addition to analysis of the activation of wsMC2R, attention was focused to the relationship of the wsMC2R ortholog and wsMC2R, specifically to the region of their interaction. Analysis of the extracellular regions of wsMC2R utilizing a chimeric receptor approach revealed that it is unlikely the N-terminal of wsMRAP1 is interacting with an extracellular region of wsMC2R. A similar chimeric receptor approach extended to the TM4 and TM5 regions of the wsMC2R ortholog revealed that the likely region of interaction between wsMC2R and wsMRAP1 to facilitate trafficking of the receptor to the plasma membrane is specific to residues within TM5. The present thesis contributes to the body of knowledge which develops a picture of the phylogenetic relationship between MC2R orthologs and MRAP orthologs of extant vertebrates.
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Hoglin, Brianne, "Characterization of the Whale Shark (Rhincodon Typus) Melanocortin-2 Receptor" (2021). Electronic Theses and Dissertations. 1942.
Received from ProQuest
Molecular biology, Endocrinology, Evolution & development