Date/Time: Tuesday, April 11^th from 9-10AM

Location: The Picower Seminar Room 46-3310

Title: Stochastic RNA editing of the Complexin C-terminus within single neurons regulates neurotransmitter release in Drosophila

Abstract: Neurotransmitter release requires assembly of the SNARE complex machinery, with multiple SNARE-binding proteins regulating this process to control when and where synaptic vesicle fusion occurs. The synaptic protein Complexin (Cpx) controls spontaneous and evoked neurotransmitter release through its ability to bind SNARE complexes and arrest SNARE zippering. Although the central SNARE-binding helix of Cpx is essential for controlling fusion, post-translational modifications to its C-terminal membrane-binding amphipathic helix modulate Cpx activity. Drosophila cpx undergoes alternative splicing of exon 7 to produce two isoforms differing in their C-terminal ~20 amino acids termed Cpx7A and Cpx7B. PKA phosphorylation of residue S126 within the Cpx7B C-terminal domain enhances spontaneous release and synaptic growth. In contrast, the more abundant Cpx7A does not undergo PKA phosphorylation but is subject to RNA editing with the C-terminus that generates three potential amino acid substitutions (N130S, N130D, N130G). Here, we used CRISPR and transgenic rescue to examine the functional significance of Cpx alternative splicing and RNA editing. Either Cpx7A or Cpx7B could support baseline synaptic transmission despite significant differences in their expression levels. RNAseq from single motoneurons revealed multiple Cpx7A edit variants are co-expressed within a cell, indicating RNA editing acts stochastically to generate a range of edited Cpx proteins within individual neurons. Cpx7A^N130S variants displayed reduced clamping function and acted dominantly when co-expressed with unedited Cpx, suggesting RNA editing can fine-tune presynaptic output from single neurons. Together, these data indicate Cpx7A and Cpx7B both support synaptic transmission, with differential RNA editing of Cpx7A altering its clamping properties to adjust neurotransmitter release and presynaptic output.