Abstract
BackgroundSynapsins 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.ResultsWe 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.ConclusionSimilar 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.
Highlights
Synapsins are abundant synaptic vesicle associated phosphoproteins that are involved in the fine regulation of neurotransmitter release
Examination of the boundaries of intron 4 in the Drosophila synapsin gene When the Drosophila genome became available from the Berkeley Drosophila Genome Project (BDGP) [29] a clear single base discrepancy between the genomic sequence and the previously published sequence of a cDNA from a head cDNA library [26] was noted
(page number not for citation purposes) http://www.biomedcentral.com/1471-2202/7/76 which predicts an open reading frame containing an RRFS motif compatible with the consensus pattern for phosphorylation by protein kinase A (PKA), [RK](2)-x-[ST] (Prosite). It seemed that the pattern RRxS, which is found in the N-terminal A-domain of all known synapsin isoforms of both vertebrates and invertebrates, is conserved in the Drosophila synapsin
Summary
Synapsins are abundant synaptic vesicle associated phosphoproteins that are involved in the fine regulation of neurotransmitter release. After the discovery of RNA editing in the kinetoplastid of typanosomes nearly two decades ago [1], similar processes have been observed for a large number of genes from different species. Most examples of nuclear pre-mRNA editing in higher eukaryotes employ adenosine to inosine (A-to-I) conversion which is generally discovered by an adenosine vs guanosine discrepancy between genomic and cDNA sequences because inosine and guanosine both pair with cytidine during cDNA synthesis by reverse transcriptase. In Drosophila melanogaster deletions in the only gene (Adar) with homology to ADARs cause severe behavioural abnormalities and neurological symptoms including temperature-sensitive paralysis, uncoordinated movements, and tremors [7]. Many known target genes of ADAR in Drosophila are involved in fast electrical and chemical neurotransmission, indicating that RNA editing by ADAR in this species may be of particular relevance for nervous system function [8,9]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
