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

• Main Authors: Buchner Erich, Zars Troy, Werner Ursula, Hoppe Jürgen, Nieratschker Vanessa, Diegelmann Sören
• Format: Article
• Language: English
• Published: BMC 2006-11-01
• Series: BMC Neuroscience
• Online Access: http://www.biomedcentral.com/1471-2202/7/76

<p>Abstract</p> <p>Background</p> <p>Synapsins are abundant synaptic vesicle associated phosphoproteins that are involved in the fine regulation of neurotransmitter release. The <it>Drosophila </it>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.</p> <p>Results</p> <p>We demonstrate that the N-terminal phosphorylation consensus motif RRxS that is conserved in all synapsins investigated so far, is modified in <it>Drosophila </it>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 <it>Drosophila Adar </it>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 <it>Drosophila</it>. 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.</p> <p>Conclusion</p> <p>Similar to several other neuronal proteins of <it>Drosophila</it>, 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 <it>Drosophila </it>is required for various forms of behavioural plasticity, it will be fascinating to investigate the effect of this recoding on learning and memory.</p>