2023 Fiscal Year Research-status Report
Synaptic vesicle transport revealed by electrophysiological and imaging studies
| Project/Area Number |
21K06445
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| Research Institution | Okinawa Institute of Science and Technology Graduate University |
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Principal Investigator |
MAHAPATRA Satyajit 沖縄科学技術大学院大学, 細胞分子シナプス機能ユニット, スタッフサイエンティスト (40832861)
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| Co-Investigator(Kenkyū-buntansha) |
DUTTA Soumyajit 沖縄科学技術大学院大学, 細胞分子シナプス機能ユニット, ポストドクトラルスカラー (20899372) [Withdrawn]
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| Project Period (FY) |
2021-04-01 – 2025-03-31
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| Keywords | Vesicle transport / the calyx of Held / hippocampal CA1 synapse / endocytosis / release site clearance / synaptic depression / recovery from STD / physiological condition |
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| Outline of Annual Research Achievements |
To understand the synaptic vesicle (SV) transport mechanism, we first tested the proteins/molecules that delay the recovery from STD kinetics of EPSCs at functionally diverse mature synapses in physiological conditions. However, we found neither the endocytic block nor the presynaptic scaffold machinery inhibition had any delaying effect on the recovery from STD kinetics, in clear contrast to previous reports carried out in non-physiological conditions and at immature calyx (Hosoi et al., Neuron 2009; Sakaba et al., PNAS 2013).
This work revealed an unexpected role of release site clearance to counter rapid synaptic depression at the calyx, carried out exclusively by fast endocytosis that was unknown at the mammalian central synapses. At the calyx, in addition to the endocytic release-site clearance, we found endocytosis-independent scaffold machinery is also necessary for rapid vesicular recruitment, and these two mechanisms cooperate to maintain synaptic strength particularly at the early phase of neurotransmission. However, at the relatively slow hippocampal CA1 synapse, only endocytosis is necessary to boost synaptic facilitation, and scaffold machinery has no effect. These findings suggest endocytic site clearance can be a universal phenomenon supporting vesicular replenishment at both fast and slow synapses, whereas the scaffold machinery plays a specialized role in vesicle replenishment, particularly at fast synapses (Mahapatra S and Takahashi T, eLife, reviewed pre-print currently).
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Unlike previous reports, at mature synapses and in physiological conditions, we didn’t observe the phenomenon we set to dissect the SV transport mechanism. This finding led us to delve further into the physiology of vesicular replenishment by endocytic site-clearance and presynaptic scaffold mechanisms at two distinct central synapses, fast calyx of Held and relatively slow hippocampal CA1 synapses.
We have concluded this work, which is currently in the final publication stage (https://elifesciences.org/reviewed-preprints/90497v3).
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| Strategy for Future Research Activity |
Our recent work (Mahapatra S and Takahashi T, eLife, reviewed pre-print currently), raises new questions that I would like to address next.
In 1.3 mM [Ca2+] under physiological conditions, we observed short-term facilitation at the hippocampal CA1 synapse, masking synaptic depression. However, no established method is available to test the recovery from depression at a facilitatory synapse to assess the vesicular recycling mechanism. Therefore, I would first develop a method to test this in physiological conditions and examine the underlying role of endocytic and scaffold proteins. This would provide a crucial insight about the mechanism underlying vesicular recycling at this bouton type slow synapse, intrinsically linked to memory formation and retention.
Additionally, we observed that physiologically, vesicular recruitment at the calyx presynaptic active zone starts as fast as within 10 milliseconds. However, how the calyx release machinery adapted to respond so fast to support rapid neurotransmission remains unknown, which I would start investigating.
As Prof. Takahashi, where I was working on this project, has retired recently, I’ve joined Prof. Wickens lab at OIST from April 2024.
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| Causes of Carryover |
Due to medical reasons, couldn't attend the international conferences last year and the saved money would be used for the reagents, attending conferences, and publication costs for the upcoming project.
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