Retrograde regulation of activity-dependent synaptic growth by Synaptotagmin 4

Ca2+ influx into pre- and post-synaptic compartments during neuronal activity is a key mediator of neurotransmitter release and synaptic plasticity. Although the role of presynaptic Ca2+ in triggering vesicle fusion is established, molecular mechanisms that underlie responses to postsynaptic Ca2+ remain unknown. The Synaptotagmin family of Ca2+ sensors includes several evolutionarily conserved neuronal isoforms that are predicted to regulate vesicle fusion, including the synaptic vesicle Ca2+ sensor Synaptotagmin 1. Recently, the Synaptotagmin 4 (Syt 4) isoform was localized to postsynaptic vesicles at Drosophila neuromuscular junctions (NMJs), suggesting a role in Ca2+-dependent release of retrograde signals. Here we demonstrate that fusioncompetent Syt 4 vesicles localize postsynaptically in Drosophila central nervous system (CNS) neurons, suggesting Syt 4 may be a general regulator of postsynaptic vesicle trafficking. Syt 4 mRNA and protein levels are bi-directionally regulated by neuronal activity, with seizure induction increasing Syt 4 levels and decreased activity reducing Syt 4 expression. Bi-directional manipulations of postsynaptic Syt 4 levels in vivo demonstrate that it regulates synaptic growth at NMJs, with Syt 4 mutants showing reduced varicosity number. Postsynaptic over-expression of Syt 4 enhances synaptic growth and requires Ca2+ binding by both the C2A and C2B domains, as well as serine 284, an evolutionarily conserved substitution for a key C2A Ca2+-binding aspartic acid found in other synaptotagmin isoforms. In addition, Syt 4 is required for activitydependent structural plasticity at NMJs, including seizure-induced and temperaturedependent synaptic growth. These findings suggest retrograde vesicular trafficking mediated by Syt 4 contributes to activity-dependent growth of neuronal connections.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Biology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Barber, Cynthia F

Advisor dc:contributor.advisor

• J. Troy Littleton.

• Biology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/46653

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/46653