Functional nanoscopy of the synaptic active zone

• Applicant: Professor Dr. Robert J. Kittel
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 286415047

• Final Report Year: 2021

Final Report Abstract

Information processing by the nervous system depends on neurotransmitter release from synaptic vesicles (SVs) at the highly specialized presynaptic active zone (AZ). The precise molecular architecture of AZs gives rise to different structural and functional AZ states, which shape chemical neurotransmission and fundamentally influence brain function. Despite a gradually emerging comprehensive AZ protein catalogue, we still lack basic mechanistic information describing how the nanoscopic organisation and functional interactions of proteins determine AZ physiology. To a large extent, this is due to the diffraction-limited resolution of conventional light microscopy, which has hindered access to the spatial nanodomain in a physiologically relevant context and to experimental difficulties of studying AZ function in vivo. The present research project set out to study how function is encoded in the ultrastructure of AZs. Focusing on Drosophila melanogaster, the experiments took advantage of the powerful tools for manipulating the fruit fly genome and exploited the experimental accessibility of the larval peripheral nervous system. The technology-driven research program focussed on two central work packages. (i) A genetic screen was combined with electrophysiology and superresolution microscopy to characterize molecular mechanisms of AZ plasticity. (ii) New optogenetic approaches were introduced to manipulate synaptic activity in the intact, freely moving organism. The main results identified the conserved SNARE regulator Complexin (Cpx) as a functional interaction partner of the core AZ component Bruchpilot (Brp). Cpx and Brp promote SV recruitment to the filamentous AZ cytomatrix and counteract short-term synaptic depression. Combined with a comparative analysis of mouse ribbon synapses, these findings support an evolutionarily conserved role of Cpx upstream of SNARE complex assembly. In terms of technological advances, highly efficient optogenetic effectors based on Channelrhodopsin-2 derivatives and the photoactivated adenylyl cyclase bPAC were developed. Together with innovative photostimulation strategies, these tools provide new opportunities for studying AZ physiology in a behavioural context.

Publications

• (2017) Drosophila active zones: from molecules to behaviour. Neurosci Res 127:14-24
  Ehmann N, Owald D, Kittel RJ
  
• 2017) Mechano-dependent signaling by Latrophilin/CIRL quenches cAMP in proprioceptive neurons. eLife 6:e28360
  Scholz N, Guan C, Nieberler M, Grotemeyer A, Maiellaro I, Gao S, Beck S, Pawlak M, Sauer M, Asan E, Rothemund S, Winkler J, Prömel S, Nagel G, Langenhan T, Kittel RJ
  
• (2018) Synthetic light-activated ion channels for optogenetic activation and inhibition. Front Neurosci 12:643
  Beck S, Yu-Strzelczyk J, Pauls D, Constantin OM, Gee CE, Ehmann N, Kittel RJ, Nagel G, Gao S
  
• (2019) Complexin cooperates with Bruchpilot to tether synaptic vesicles to the active zone cytomatrix. J Cell Biol 218:1011-1026
  Scholz N, Ehmann N, Sachidanandan D, Imig C, Cooper BH, Jahn O, Reim K, Brose N, Meyer J, Lamberty M, Altrichter S, Bormann A, Hallermann S, Pauli M, Heckmann M, Stigloher C, Langenhan T, Kittel RJ
  
• (2019) Implications of the Sap47 null mutation for synapsin phosphorylation, longevity, climbing proficiency and behavioural plasticity in adult Drosophila. J Exp Biol 222:19
  Blanco-Redondo B, Nuwal N, Kneitz S, Nuwal T, Halder P, Liu Y, Ehmann N, Scholz N, Mayer A, Kleber J, Kähne T, Schmitt D, Sadanandappa MK, Funk N, Albertova V, Helfrich-Förster C, Ramaswami M, Hasan G, Kittel RJ, Langenhan T, Gerber B, Buchner E
  
• (2020) Active zone compaction in presynaptic homeostatic potentiation. bioRxiv
  Mrestani A, Kollmannsberger P, Pauli M, Repp F, Kittel RJ, Eilers J, Doose S, Sauer M, Sirén A-L, Heckmann M, Paul MM
  
• (2020) Antinociceptive modulation by the adhesion GPCR CIRL promotes mechanosensory signal discrimination. eLife 9:e56738
  Dannhäuser S, Lux TJ, Hu C, Selcho M, Chen JT-C, Ehmann N, Sachidanandan D, Stopp S, Pauls D, Pawlak M, Langenhan T, Soba P, Rittner HL, Kittel RJ
  
• (2020) Smartphone optogenetics: Controlling the behaviour of Drosophila melanogaster using smartphone displays. Sci Rep 10:17614
  Meloni I, Sachidanandan D, Thum AS, Kittel RJ, Murawski C