Mutations in synapsin IIa reveal ATP- dependent regulation of synaptic vesicle clustering and recruitment

Y. P. Shulman, D. Gitler

Research output: Contribution to journalMeeting Abstract

Abstract

The capability of synapses to maintain neurotransmission
during intense activity depends on the replenishment of the
active zone with ready vesicles. The availability of primed
vesicles is dynamically determined by their usage and subsequent reconstitution, the latter occurring either by endocytosis
or by the recruitment of stored pre-existing vesicles. Consequently, a reasonable assumption is that enlargement of the
total vesicle store should enhance transmission, especially
during periods of heavy use. Supporting this expectation is
the past observation that knocking out the synapsin genes both
perturbs the cluster of vesicles near the active zone and accelerates synaptic depression. Likewise, over-expressing
synapsins IIa enlarges the vesicle cluster and retards synaptic
depression. Here we describe mutations in synapsin IIa which
do not concur with this hypothesis. Semi-quantitative
synaptobrevin 2 immunostaining of cultured hippocampal
neurons revealed that a mutation that annuls ATP-binding to
the "C" domain of synapsin IIa (K270Q) substantially enhances its capability to cluster vesicles, without affecting
vesicle mobility, as evidenced by FRAP measurements. Although more vesicles are present, electrophysiological recordings of synaptic currents in autaptic neurons revealed faster
synaptic depression during high-frequency stimulation, without evidence for a change in the initial release probability. This
suggests a deficit in vesicle resupply. A contrasting result was
obtained with a phosphomimetic mutation (S10E) of the wellconserved PKA phosphorylation site in synapsin IIa, which
enhanced vesicle clustering without affecting synaptic depression, whereas a mutation annulling phosphorylation (S10A)
accelerated depression without enhancing clustering. Therefore, the mere presence of vesicles is insufficient to predict
vesicle availability; our results implicate the dynamics of ATP
within individual terminals in locally regulating vesicle
recruitment.
Original languageEnglish
Pages (from-to)S116-S116
JournalJournal of Molecular Neuroscience
Volume53
Issue number1
DOIs
StatePublished - Aug 2014

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