Date of Award

Winter 3-21-2026

Document Type

Dissertation

Degree Name

Ph.D. in Biological Sciences

Organizational Unit

College of Natural Science and Mathematics, Biological Sciences

First Advisor

Cedric S. Asensio

Copyright Statement / License for Reuse

All Rights Reserved
All Rights Reserved.

Keywords

Insulin secretion, Synaptotagmins, Cleavage, Trafficking

Abstract

Understanding the traffic and function of proteins found on large dense core vesicles is crucial in determining how neuroendocrine cells regulate secretion of peptides and peptide hormones. A family of transmembrane proteins called Synaptotagmins, which consist of a short N-terminal luminal domain, a single transmembrane domain, and two C2 cytoplasmic domains, many of which function as calcium (Ca2+) sensors, are directly involved in regulated secretion. In INS-1 832/13 cells, Syt-7 and Syt-9 are the two Ca2+--sensing synaptotagmins expressed and involved in Ca2+-dependent exocytosis. We identify that Syt-7 is cleaved within its transmembrane domain by γ-secretase, and that this cleavage is required for proper regulated secretion. In the absence of Syt-7 cleavage, WT INS-1 832/13 cells behave functionally the same as Syt-7 KO INS-1 832/13 cells. We have also determined that Syt-7 is cleaved by γ-secretase by directly trafficking from the TGN to the plasma membrane, followed by endocytosis to a γ- secretase-positive early endosome, before sorting onto insulin granules. Furthermore, we have identified that cleaved Syt-7 can interact with t-SNARE protein Syntaxin-1, while uncleaved Syt-7 cannot, offering an explanation for why Syt-7 cleavage is important. Subsequent investigation into Syt-9 resulted in identification of a similar trafficking route consisting of the TGN to the plasma membrane, followed by the endocytic pathway prior to sorting onto insulin granules. While we report preliminary data on potential cleavage of Syt-9, we have been unable to determine the mechanism of cleavage since γ-secretase is not involved. Additionally, we have begun to investigate the phosphorylation of Syt-9 by PKC and its impact on Syt-9 traffic to insulin granules. Finally, despite conflicting reports in established literature for Syt-9’s role in Ca2+-dependent exocytosis, we report that Syt-9 appears to be either uninvolved or inhibitory during short-term high K+ secretion, while being important for sustained glucose-stimulated secretion.

Copyright Date

3-2026

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Theodore Carter

Provenance

Received from ProQuest

File Format

application/pdf

Language

English (eng)

Extent

135 pgs

File Size

23.8 MB

Download

Available for download on Friday, April 14, 2028



Included in

Cell Biology Commons

Share

COinS