Drosophila synaptotagmin I null mutants survive to early adulthood

Synaptotagmin is a synaptic vesicle protein required for efficient neurotransmitter release, yet its exact role in the synaptic vesicle cycle is unclear. Drosophila presents an ideal organism for studies aimed at determining the in vivo functions of proteins. However, synaptotagmin studies have been limited by the early (embryonic or first instar) lethality previously reported for Drosophila synaptotagmin I null (syt(null)) mutants. Here we report a new culturing technique that enhances survival of severely uncoordinated mutants thereby permitting Drosophila syt(null) mutants to survive through early adulthood. We examined synapses in syt(null) third instar larvae by electrophysiology and found that they exhibit severely decreased and asynchronous evoked neurotransmitter release, as well as an increased rate of spontaneous neurotransmitter release, as previously seen in first instar syt(null) larvae. The ability to examine severe synaptotagmin mutants as third instar larvae, a stage where electrophysiological and morphological analyses are more easily accomplished, will facilitate structure/function studies.