Title

Post-transcriptional modification of Drosophila synaptotagmin 1: A calcium sensor for neurotransmitter release

Date of Completion

January 2006

Keywords

Biology, Genetics

Degree

Ph.D.

Abstract

Synaptic transmission between neurons involves fast synchronous neurotransmitter release, triggered by calcium influx into the nerve termini. Synaptotagmin 1 (Syt 1), a phospholipid-binding protein, was identified as the intermediate calcium sensor responsible for such release. Post-transcriptional modification of syt 1 involves alternative RNA splicing and RNA editing. Syt 1 undergoes alternative splicing to either include or exclude a short six base pair exon VQ, which codes for valine and glutamine amino-acid residues. The C2B domain of Drosophila Syt 1 contains four editing sites (Sites A, B, C and D) located in invariant and conserved regions of exon 9. I report here that both RNA editing and alternative splicing of syt 1 are developmentally regulated in Drosophila melanogaster, such that RNA editing and the exclusion of alternatively spliced exon VQ are adult-specific; suggesting possible roles of RNA editing and exon VQ exclusion in fly development. Using targeted transgenic expression of fully edited (G4) and fully unedited (A4) syt 1 constructs with or without the inclusion of exon VQ (+VQ or -VQ) in D. melanogaster. I attempt to determine possible effects of RNA editing and alternative splicing on Syt 1 function. ^ Ubiquitous expression of both A4 and G4 transgenes with Tubulin Ga14 driver, in either +VQ or -VQ background, is lethal in wild type files. However, lethality occurs at the L1 and L2 stages in A4 transgenic flies, whereas, G4 transgenic flies die as pharate adults unable to eclose. We speculate from this result that editing regulates Syt 1 function by reducing Syt 1 activity. I also report the first complete rescue of lethality and viability in Syt 1 null mutant flies using targeted neuronal expression of G4 and A4 syt 1 transgenes. There are significant differences in courtship/mating behavior among flies carrying G4 and A4 Syt 1 transgenes, with the A4 rescued males showing aberrant courtship behavior. I propose that editing of Drosophila syt 1 may control complex behavioral phenotypes such as courtship/mating behavior. ^