Erich Buchner group
Synaptic proteins of Drosophila: Identification, gene structure, functional characterization.
Network analysis with DNA-encoded probes: Classical and operant conditioning
Staff: Beatriz Blanco (PhD student)
We are interested in mechanisms of synaptic transmission and its modulation during learning and memory, and in the processes that lead to synapse malfunction during ageing and neurodegeneration. In addition we use genetic tools to analyze neuronal networks involved in olfactory and locomotor conditioning.
The release of neurotransmitters from the presynaptic nerve terminal involves complex molecular mechanisms effecting the directed movement and docking of transmitter-loaded vesicles to the presynaptic membrane, a maturation process (priming), and the calcium-triggered exocytotic fusion of the vesicles with the presynaptic membrane to secrete the transmitter into the synaptic cleft. The fine regulation of these processes presumably is essential for higher brain function including feature abstraction, learning and memory, and cognition. We use monoclonal antibodies (MABs) from an extensive hybridoma library generated against Drosophila brain (Hofbauer, 1991; Hofbauer et al., 2009; Halder et al., 2011) to identify proteins that are specifically located at synapses in the Drosophila nervous system (Fig. 1).
Main research projects
Synapsins are abundant synaptic vesicle-associated phosphoproteins which have been extensively investigated in vertebrates. The mammalian genome contains three synapsin genes that generate multiple isoforms. Several studies implicate that synapsins may be involved in neurotransmitter release and synaptic plasticity by segregating the synaptic vesicles to a reserve pool and an active, releasable pool. Mice lacking synapsin I, II, III or all three genes are viable, fertile and develop rather normally but show specific alterations in synaptic ultrastructure and functional plasticity. We have cloned the single synapsin gene in Drosophila melanogaster and generated mutants (Fig. 2) in order to study its function (Godenschwege et al., 2004; Michels et al., 2005). Null mutants are viable and fertile and display no obvious structural defects but are disturbed in various forms of behavioural plasticity (with B. Gerber and H. Tanimoto). We have shown that the N-terminal protein kinase A (PKA) phosphorylation motif RRxS present in all known synapsins is encoded in Drosophila by the genome but is edited in most mRNAs by the ADAR enzyme to RGxS. An undeca-peptide representing the genomic N-terminal sequence (containing RRFS) constitutes an excellent substrate for bovine PKA, whereas a peptide with the mRNA encoded sequence (containing RGFS) is not significantly phosphorylated by bovine PKA (Diegelmann et al., 2006). In collaboration with the group of G. Lubec (Vienna) we have recently analyzed the phosphorylation of Drosophila synapsins by mass spectrometry and identified seven novel phosphorylation sites. By using phospho-specific antisera we are presently studying distribution and function of two sites.
B) Synapse-associated protein of 47kD (SAP47):
The Sap47 gene codes for a novel conserved synaptic protein identified by MAB nc46 (Fig. 3). The SAP47 protein and its vertebrate homologues contain a novel domain found also in transcription factors and several hypothetical proteins of a wide range of species extending from protozoans to human (Doerks et al., 2002). No information on the function of the SAP47 protein family is presently available either in insects or in mammals. We have generated null mutants which are viable and fertile (Funk et al., 2004) but show defects in synaptic plasticity at the behavioural and electrophysiological level (Saumweber et al. 2011). At present we are investigating interaction partner candidates in order to obtain information on the role of SAP47 and its mammalian homologue SYAP1 in synaptic plasticity and neurodegeneration (with N. Funk and M. Sendtner).
C) Bruchpilot (BRP)
The Bruchpilot protein (BRP) has been localized at the presynaptic active zone by MAB nc82 (Fig. 4) and was identified by 2D-gel electrophoresis and MALDI-TOF mass spectrometry as a homologue of the mammalian active zone protein ELKS/CAST. Reduction of the protein “Bruchpilot” (BRP) by RNAi causes defects in synaptic transmission and ultrastructure (missing T-bars) and leads to severe locomotor deficiencies (in collaboration with E. Asan, Würzburg, and the group of S. Sigrist) (Wagh et al., 2006; Kittel et al., 2006).
D) SR protein kinase 79D (SRPK79D)
When a so far uncharacterized gene coding for a protein with homology to serine/threonine protein kinases from vertebrates is mutated, conspicuous accumulations of BRP are observed in motor axons (Fig. 5). These correlate with reduced longevity (neurodegeneration?) (Nieratschker et al., 2009).
E) Optogenetics (in collaboration with A. Fiala, Göttingen)
We use DNA-encoded molecular probes for calcium and cAMP or transgenes encoding light-activated ion channels or adenylate cyclase to analyze neuronal circuitry for olfactory classical conditioning and locomotor operant learning (Riemensperger et al., 2005; Schroll et al., 2006; Bucher and Buchner, 2009).
Current external funding: GK-1156 (DFG)