Author ORCID Identifier

https://orcid.org/0009-0000-3707-4925

Date of Graduation

12-2025

Document Type

Thesis (MS)

Program Affiliation

Neuroscience

Degree Name

Masters of Science (MS)

Advisor/Committee Chair

Ruth Heidelberger, MD, PhD

Committee Member

Michael Beierlein, PhD

Committee Member

Shin Nagayama, PhD

Committee Member

Qingchun Tong, PhD

Committee Member

Kartik Venkatachalam, PhD

Abstract

Calcium binding protein 5 (CaBP5) is a retina-specific protein, specifically expressed in rod bipolar cells and in type 3 OFF and type 5 ON cone bipolar cells. Rod bipolar cells (RBCs) are essential for rod pathway signaling in the vertebrate retina, and they form ribbon style synapses that enable the continuous transmission of visual information. These synapses rely on SNARE complexes formed between SNAP25, synaptobrevin, and the retina-specific syntaxin isoform, syntaxin-3B. Syntaxin-3B can be phosphorylated at T14 via calcium/calmodulin dependent protein kinase II (CaMKII) in a calcium-dependent manner. Given its structural similarities to calmodulin (CaM), CaBP5 may act on CaM effectors and substitute functionally. Notably, CaBP5⁻/⁻ mice exhibited reduced sensitivity in rod-mediated responses in ganglion cells, suggesting a role in regulating neurotransmitter release at the presynaptic RBC terminals. Using membrane capacitance measurements in the acutely isolated RBCs, we found that the total number of fusion-competent vesicles in RBCs was not different between CaBP5⁻/⁻ and wild-type mice. However, CaBP5-/- RBCs showed a greater rise in membrane capacitance in response to a train of depolarization pulses and faster refilling of the rapidly releasable pool compared to the wild-type. Together, these findings provide an insight into the role of CaBP5 in regulating synaptic vesicle dynamics at the ribbon-style synapses of the RBC.

Keywords

exocytosis, ribbon synapse, SNARE proteins, retina

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