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Poster Full Abstracts - Neurophysiology and Behavior
Poster board number is above title. The first author is the presenter
306
Angelman syndrome is caused by maternal loss of the ubiquitin ligase gene
UBE3A
, while maternally derived duplications encompassing
UBE3A
can
cause autism. We studied the elecrophysiological effects of
Drosophila UBE3A
(
Dube3a
) loss and over-expression using the larval neuromuscular junction
(NMJ). We measured spontaneous, mini-excitatory junction potentials (mEJPs) and evoked excitatory junction potentials (EJPs) using the A3 region of third
instar larvae. Over-expression of Dube3a using the neuronal driver
elav
-GAL4 increased mEJP amplitude, while flies deficient for
Dube3a
(i.e.
Dube3a
15b
homozygotes) had fewer mEJPs of a lower amplitude when compared to wild type. In addition, we found that a Dube3a construct that was not able to
ubiquitinate substrates (
Dube3a
-C/A) did not result in high amplitude mEJPs and the number again approached wild type levels indicating that the ubiquitin
ligase function of Dube3a is required for the high amplitude mEJP phenotype. The total number of synaptic active zones per bouton and number of boutons
per muscle area were not affected by increased Dube3a levels, and an analysis of presynaptic terminal vesicle size suggests that the increased mEJPs may
result from increased synaptic vesicle diameter. The average amplitude of rapidly evoked EJPs (15 Hz) decreased more rapidly after the beginning of
stimulation in Dube3a over-expressing larvae compared to controls. The significant rapid decline in average EJP amplitude primarily resulted from an
increase in the failure rate of evoked responses. Occasionally in control animals, large spontaneous depolarizations similar in amplitude to evoked EJPs were
observed. These were blocked by TTX and thus may have resulted from spontaneous motor neuron firing. In Dube3a over expressing larvae, there was a
significant increase in this putative spontaneous neuronal firing. Our findings suggest that Dube3a may regulate neurotransmitter release and neuronal
excitability in a ubiquitin dependent manner.
655A
The synaptic vesicle-associated Ca
2+
channel Flower couples synaptic exo-endocytosis cycle and regulates synaptic growth.
Chi-Kuang Yao
1,2,3
, Yong
Qi Lin
2,3
, Claire Haueter
2,3
, Hugo J Bellen
2,3
. 1) Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan; 2) Department of Molecular and Human
genetics, Baylor college of medicine, Houston, TX, USA; 3) HHMI.
Synaptic function and growth are two key components for synaptic plasticity that has been implicated in learning and memory. Synaptic function is
achieved by synaptic vesicle (SV) exocytosis that, in response to action potentials, elicits a fusion of SV with the presynaptic membrane, leading to the
release of neurotransmitters to provoke postsynaptic responses. SVs must then be properly endocytosed to sustain repeated transmission. Hence, a tight
coupling of exo- to endocytosis is critical for synaptic function. Yet how this coupling is controlled remains poorly understood. Our previous work (Yao et
al., Cell 2009, 138(5):947-60) has shown that the SV-associated Ca
2+
channel Flower (Fwe) promotes synaptic endocytosis and thereby couples exo- to
endocytosis. Intriguingly, loss of
fwe
also leads to synaptic outgrowth at larval neuromuscular junctions (NMJs), characterized as a increased number of
satellite boutons, similar to those observed in many endocytic mutants, including
shi
,
synj
,
endo
,
dap160
, and
lap
. The similarity in phenotype suggests that
these endocytic proteins may govern a common cellular machinery underlying SV endocytosis and synaptic growth. However, what these cellular
mechanisms are is still unclear. More recently, we have been focusing on understanding the mechanisms underlying Fwe-mediated synaptic growth. Our
results indicate that the Ca
2+
influx triggered by Fwe is required for synaptic endocytosis but not growth, suggesting that Fwe has two distinct cellular
functions. We are attempting to explore mechanisms underlying these two processes.