Calcium Binding Protein (CaBP5) on Synaptic Vesicle Dynamics in Rod Bipolar Cells in the Retina

Qingying (Cathy) Jiang (Advisor: Ruth Heidelberger, MD, PhD) 

          Calcium binding protein 5 (CaBP5) is a retina-specific protein, specifically expressed in the rod bipolar cells, 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 synapse that enable continuous transmission of visual information. These synapses rely on the SNARE complex formed between SNAP25, synaptobrevin, and the retina-specific 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 reduction in the light sensitivity in the downstream rod-mediated ganglion cells, suggesting a role in regulating neurotransmitter release at the presynaptic RBC terminals. Using membrane capacitance measurement in the acutely isolated RBCs, we found that the total number of ribbon-associated vesicles was not different between CaBP5?/? and wild-type. However, CaBP5^-/- RBCs had greater cumulative release during a train stimulation and faster refilling rate of the rapidly releasable pool compared to the wild-type. Together, these findings provide an insight on the role of CaBP5 in regulating synaptic vesicle dynamics at the ribbon-style synapse of the RBC terminal.

Advisory Committee:

• Ruth Heidelberger, MD, PhD, Chair
• Michael Beierlein, PhD
• Shin Nagayama, PhD
• Qingchun Tong, PhD
• Kartik Venkatachalam, PhD

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