The conserved protein kinase-A target motif in synapsin of Drosophila is effectively modified by pre-mRNA editing

Sören Diegelmann^*¹ , Vanessa Nieratschker^*¹ , Ursula Werner^{^}, Jürgen Hoppe² , Troy Zars³ and Erich Buchner¹

¹Lehrstuhl für Genetik und Neurobiologie, Theodor Boveri Institut für Biowissenschaften der, Universität Würzburg, Würzburg, Germany

²Lehrstuhl für Physiologische Chemie, Theodor Boveri Institut für Biowissenschaften der, Universität Würzburg, Würzburg, Germany

³Division of Biological Sciences, University of Missouri-Columbia, Columbia, USA

author email corresponding author email^Deceased * Contributed equally

BMC Neuroscience 2006, 7:76doi:10.1186/1471-2202-7-76


Published:	14 November 2006

Abstract

Background

Synapsins are abundant synaptic vesicle associated phosphoproteins that are involved in the fine regulation of neurotransmitter release. The Drosophila member of this protein family contains three conserved domains (A, C, and E) and is expressed in most or all synaptic terminals. Similar to mouse mutants, synapsin knock-out flies show no obvious structural defects but are disturbed in complex behaviour, notably learning and memory.

Results

We demonstrate that the N-terminal phosphorylation consensus motif RRxS that is conserved in all synapsins investigated so far, is modified in Drosophila by pre-mRNA editing. In mammals this motif represents the target site P1 of protein kinase A (PKA) and calcium/calmodulin dependent protein kinase I/IV. The result of this editing, by which RRFS is modified to RGFS, can be observed in cDNAs of larvae and adults and in both isolated heads and bodies. It is also seen in several newly collected wild-type strains and thus does not represent an adaptation to laboratory culture conditions. A likely editing site complementary sequence is found in a downstream intron indicating that the synapsin pre-mRNA can form a double-stranded RNA structure that is required for editing by the adenosine deaminase acting on RNA (ADAR) enzyme. A deletion in the Drosophila Adar gene generated by transposon remobilization prevents this modification, proving that the ADAR enzyme is responsible for the pre-mRNA editing described here. We also provide evidence for a likely function of synapsin editing in Drosophila. The N-terminal synapsin undeca-peptide containing the genomic motif (RRFS) represents an excellent substrate for in-vitro phosphorylation by bovine PKA while the edited peptide (RGFS) is not significantly phosphorylated. Thus pre-mRNA editing by ADAR could modulate the function of ubiquitously expressed synapsin in a cell-specific manner during development and adulthood.

Conclusion

Similar to several other neuronal proteins of Drosophila, synapsin is modified by ADAR-mediated recoding at the pre-mRNA level. This editing likely reduces or abolishes synapsin phosphorylation by PKA. Since synapsin in Drosophila is required for various forms of behavioural plasticity, it will be fascinating to investigate the effect of this recoding on learning and memory.