Quantifying the synaptic Ca2+-binding kinetics of Synaptotagmin-1, the Ca2+ sensor for transmitter release in the forebrain
Final Report Abstract
Neurons of the central nervous system communicate with each other via calciummediated release of chemical neurotransmitters from presynaptic terminals. Calcium enters a presynaptic terminal through voltage-gated channels, binds to a specialized calcium sensor protein (synaptotagmin, Syt), which is bound to the transmitter-filled vesicles and triggers their fusion. The spatial relationship between the calcium channels and the vesicles as well as the calcium binding kinetics of the sensor protein are essential determinants for the reliability and plasticity of the synaptic transmission process. Quantitative details on this were previously lacking for synapses in the cerebral cortex and were the subject of this project. In the project, we focused on synapses between pyramidal cells of the neocortex. We found a surprisingly high reliability of these synapses. We could largely explain this high reliability by elucidating the structure of the calcium signaling domains and the positional relationships between different channel subtypes and the transmitter-filled vesicles in the course of postnatal maturation of the synapses. We also found a developmental transition from loose microdomain coupling to very tight nanodomain coupling. Finally, our results showed that in the immature cortex, N- and P/Q-subtype channels trigger release, whereas in the mature cortex, only P/Q-type channels remain. These structural changes were accompanied by functional changes, particularly in synaptic plasticity. Regarding the release sensors, Syt1 and Syt2 are the main isoforms for fast calcium-mediated neurotransmission in the brain. However, the calcium binding kinetics had previously only been studied for Syt2, the hindbrain sensor. In contrast, the synaptic binding kinetics of Syt1, the dominant isoform of the cerebral cortex, had not yet been quantified. In the project, we succeeded in quantifying the calcium binding kinetics of Syt1-mediated transmitter release, finding significant differences to Syt2-mediated transmitter release. Together with the above findings, these differences are suitable to explain the high reliability of neocortical synapses. Overall, the project has thus elucidated important unknowns for our understanding of synaptic information flow and its regulation by plasticity at a synapse in the cerebral cortex.
Publications
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Neocortical High Probability Release Sites Are Formed by Distinct Ca2+ Channel-to-Release Sensor Topographies during Development. Cell Reports, 28(6), 1410-1418.e4.
Bornschein, Grit; Eilers, Jens & Schmidt, Hartmut
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Synaptotagmin Ca2+ Sensors and Their Spatial Coupling to Presynaptic Cav Channels in Central Cortical Synapses. Frontiers in Molecular Neuroscience, 11.
Bornschein, Grit & Schmidt, Hartmut
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Developmental Increase of Neocortical Presynaptic Efficacy via Maturation of Vesicle Replenishment. Frontiers in Synaptic Neuroscience, 11.
Bornschein, Grit; Brachtendorf, Simone & Schmidt, Hartmut
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Calcium dependence of neurotransmitter release at a high fidelity synapse. eLife, 10.
Eshra, Abdelmoneim; Schmidt, Hartmut; Eilers, Jens & Hallermann, Stefan
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The intracellular Ca2+sensitivity of transmitter release from neocortical boutons. Cold Spring Harbor Laboratory.
Bornschein, Grit; Brachtendorf, Simone; Eshra, Abdelmoneim; Kraft, Robert; Eilers, Jens; Hallermann, Stefan & Schmidt, Hartmut
