F. Kawasaki et al., Synaptic physiology and ultrastructure in comatose mutants define an in vivo role for NSF in neurotransmitter release, J NEUROSC, 18(24), 1998, pp. 10241-10249
N-Ethylmaleimide-sensitive fusion protein (NSF) is a cytosolic protein thou
ght to play a key role in vesicular transport in all eukaryotic cells. Alth
ough NSF was proposed to function in the trafficking of synaptic vesicles r
esponsible for neurotransmitter release, only recently have in vivo experim
ents begun to reveal a specific function for NSF in this process. Our previ
ous work showed that mutations in a Drosophila NSF gene, dNSF1, are respons
ible for the temperature-sensitive paralytic phenotype in comatose (comt) m
utants. In this study, we perform electrophysiological and ultrastructural
analyses in three different comt alleles to investigate the function of dNS
F1 at native synapses in vivo. Electrophysiological analysis of postsynapti
c potentials and currents at adult neuromuscular synapses revealed that in
the absence of repetitive stimulation, comt synapses exhibit wild-type neur
otransmitter release at restrictive (paralytic) temperatures. In contrast,
repetitive stimulation at restrictive temperatures revealed a progressive,
activity-dependent reduction in neurotransmitter release in comt but not in
wild type. These results indicate that dNSF1 does not participate directly
in the fusion of vesicles with the target membrane but rather functions in
maintaining the pool of readily releasable vesicles competent for fast cal
cium-triggered fusion. To define dNSF1 function further, we used transmissi
on electron microscopy to examine the distribution of vesicles within synap
tic terminals, and observed a marked accumulation of docked vesicles at res
trictive temperatures in comt. Together, the results reported here define a
role for dNSF1 in the priming of docked synaptic vesicles for calcium-trig
gered fusion.