Date of Award

Spring 2015

Degree Name

Bachelor of Science

Major

Biology

First Advisor

Robert Fleming

Second Advisor

Kent Dunlap

Third Advisor

Terri Williams

Abstract

The Notch signaling pathway is a crucial means by which organisms differentiate cells during development. Notch is regulated primarily through the interaction of a Notch receptor protein and a ligand protein, in two specific ways. Cis-inhibition occurs when both a ligand and receptor are present on the same cellular membrane. This results in the cis-ligand binding to the receptor and preventing the ligand on an adjacent cell from binding and activating the receptor. Alternatively, trans-activation occurs when the ligand and receptor are on adjacent cells, and results in the activation of the Notch pathway. Both the receptor and ligand proteins are transmembrane proteins that are cleaved first extracellularly by a metalloprotease, and then intracellularly by a γ-secretase. While the cleavages in the receptor protein have been found to be crucial for proper Notch activation, the role of the ligand cleavages is much less well defined. Previous studies have found that the cleavage rate of the ligand may be inversely correlated to Notch activation. We postulated that the extracellular cleavage of Serrate, a ligand for Notch, by a metalloprotease serves as a means of inhibiting Notch activation, possibly by affecting the endocytosis of the ligand molecule. To test this hypothesis, we replaced the transmembrane domain of a truncated form of Serrate with that region from non-cleavable human tyrosine kinase receptor DDR2 (discoidin domain-receptor 2), and show that preventing this cleavage is insufficient to restore Notch activation. These findings suggest that an additional extracellular 65 amino acid segment near the transmembrane domain may be necessary to restore wild-type levels of Notch activation.

Comments

Senior thesis completed at Trinity College for the degree of Bachelor of Science in Biology.

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