Synaptic ribbons in the terminals of sensory neurons such as hair cells, photoreceptors, and bipolar cells are specialized for continuous transmitter release and analog signal transmission. The proper function of ribbons is essential for the perception of both light and sound. While the mechanisms that regulate vesicle fusion at the ribbon synapse are increasingly well understood, the mechanisms that regulate the flow of vesicle traffic to ribbons in support of continuous release are less well known. Marshalin is a microtubule minus-end binding protein that was originally discovered by its interaction with Usher syndrome protein cadherin23 in cochleae. Antibodies to marshalin additionally show colocalization with the ribbon region of both cone photoreceptor and hair cell synaptic terminals. The close association between marshalin and synaptic ribbons suggests a role in transmitter release or vesicle mobilization. We will use marshalin conditional knockout (CKO) mice, newly obtained by Dr Jing Zheng, to test for a role of marshalin in both vision and hearing by investigating synaptic vesicle turnover. Experiments will first examine the overall morphology of auditory hair cells and cone photoreceptors in the marshalin-CKO, and then focus on the terminal region. Terminal morphology will be studied at the light microscopic level using antibodies to ribbon proteins (eg, ribeye), ribbon associated proteins (eg, Cav1.3 or 1.4), and postsynaptic glutamate receptors. Due to ease of investigation, cone photoreceptor ribbon function will be assayed in retinal slices. In slices, transmitter release is typically monitored by recording from postsynaptic Off bipolar cells which express AMPA/kainate receptors. Release will be gated either by applying light to the dark-adapted slice, or by using mice that selectively express the light sensitive protein channelrhodopsin2 in cone photoreceptors. Our prediction is that marshalin enhances the supply of vesicles to ribbons.
|Effective start/end date||7/1/14 → 9/30/16|
- American Academy of Otolaryngology-Head and Neck Surgery Foundation, Inc. (Agmt 7/10/14)
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