Physiology and plasticity of the active zone in vivo
Final Report Abstract
The Emmy Noether project “Physiology and plasticity of the active zone in vivo” set out to investigate information transfer at chemical synapses, the sub-cellular contact sites between neurons and their partner cells. Particular focus was placed on the highly specialised presynaptic region where neurotransmitter is released from synaptic vesicles, the so-called active zone (AZ). Specifically, experiments were devised to investigate structural and functional properties of the AZ and to test for their activity-dependent modulation in vivo. To this end, the study was conducted at the developing neuromuscular junction (NMJ) of Drosophila melanogaster – a synaptic system offering unique molecular, optical, and electrophysiological access. To begin with, a mechanistic interpretation was developed, which describes how the cytoskeletal matrix associated with the AZ (CAZ) contributes to the organisation of synaptic vesicle pools. Based on this work, it was identified that tethering vesicles to the filamentous core CAZ component Bruchpilot (Brp) influences short-term plasticity by preventing synaptic depression. To further improve our quantitative understanding of structure-function relationships at the AZ, super-resolution microscopy was engaged. By correlating the nanoscopic organisation of Brp with electrophysiological synaptic properties, functional signatures were identified in the CAZ ultrastructure, which deliver mechanistic information on neurotransmitter release. Importantly, a method was developed for using localisation-based light microscopy to extract protein counts from macromolecular assemblies at single molecule resolution, illustrating the potential of quantitative localisation microscopy in the Neurosciences. In parallel, the light-gated ion channel Channelrhodopsin-2 (ChR2) was employed to control neuronal activity in the intact organism. Surprising observations shifted the focus from the AZ to postsynaptic signal reception, where activity-dependent glutamate receptor dynamics were identified. This discovery can be summarised in a comprehensive physiological model, whereby Hebbian synaptic plasticity guides the molecular maturation, and sparse transmitter release controls the stabilization of individual postsynaptic receptor fields. Finally, novel ChR variants were introduced to Drosophila to characterise their functional properties in vivo. The extremely high sensitivity of these actuators offers unique possibilities for studies of synaptic plasticity in the intact organism and provides an ideal entry point to investigate how molecular mechanisms of AZ function are connected to animal behaviour.
Publications
- (2010) Mechanisms of short-term plasticity at neuromuscular active zones of Drosophila. HFSP J 4:72-84
Hallermann S, Heckmann M, Kittel RJ
- (2013) Hebbian plasticity guides maturation of glutamate receptor fields in vivo. Cell Rep 3:1407–1413
Ljaschenko D, Ehmann N, Kittel RJ
(See online at https://doi.org/10.1016/j.celrep.2013.04.003) - (2014) Channelrhodopsin-2-XXL, a powerful optogenetic tool for low light applications. Proc Natl Acad Sci USA 111:13972–13977
Dawydow A, Gueta R, Ljaschenko D, Ullrich S, Hermann M, Ehmann N, Gao S, Fiala A, Langenhan T, Nagel G, Kittel RJ
(See online at https://doi.org/10.1073/pnas.1408269111) - (2014) Quantitative super-resolution imaging of Bruchpilot distinguishes active zone states. Nat Commun 5:4650–4661
Ehmann N, van de Linde S, Alon A, Ljaschenko D, Keung XZ, Holm T, Rings A, DiAntonio A, Hallermann S, Ashery U, Heckmann M, Sauer M, Kittel RJ
(See online at https://doi.org/10.1038/ncomms5650) - (2014) Quantitatives Imaging durch molekulare Auflösung. BIOspektrum 6:618–621
van de Linde S, Ehmann N, Kittel RJ, Sauer M
(See online at https://doi.org/10.1007/s12268-014-0495-1) - (2015) Bruchpilot and Synaptotagmin collaborate to drive rapid glutamate release and active zone differentiation. Front Cell Neurosci 9:29
Paul MM, Pauli M, Ehmann N, Hallermann S, Sauer M, Kittel RJ, Heckmann M
(See online at https://doi.org/10.3389/fncel.2015.00029) - (2015) Loss of the Coffin-Lowry syndrome-associated gene RSK2 alters ERK activity, synaptic function and axonal transport in Drosophila motoneurons. Dis Model Mech 11:1389-1400
Beck K, Ehmann N, Andlauer TF, Ljaschenko D, Strecker K, Fischer M, Kittel RJ, Raabe T
(See online at https://doi.org/10.1242/dmm.021246) - (2015) Super-resolution microscopy of the synaptic active zone. Front Cell Neurosci 9:7
Ehmann N, Sauer M, Kittel RJ
(See online at https://doi.org/10.3389/fncel.2015.00007) - (2015) The Adhesion GPCR Latrophilin/CIRL shapes mechanosensation. Cell Rep 11:866–874
Scholz N, Gehring J, Guan C, Ljaschenko D, Fischer R, Lakshmanan V, Kittel RJ, Langenhan T
(See online at https://doi.org/10.1016/j.celrep.2015.04.008) - (2010) Naked dense bodies provoke depression. J Neurosci 30:14340-14345
Hallermann S, Kittel RJ, Wichmann C, Weyhersmüller A, Fouquet W, Mertel S, Owald D, Eimer S, Depner H, Schwärzel M, Sigrist SJ, Heckmann M
(See online at https://doi.org/10.1523/JNEUROSCI.2495-10.2010) - (2016) Optogenetics in Drosophila Neuroscience. Methods Mol Biol 1408:167-175
Riemensperger T, Kittel RJ, Fiala A
(See online at https://doi.org/10.1007/978-1-4939-3512-3_11) - (2016) Synaptic vesicle proteins and active zone plasticity. Front Synaptic Neurosci 8:8
Kittel RJ, Heckmann M
(See online at https://doi.org/10.3389/fnsyn.2016.00008)
