R. Ranjan et al., CYSTEINE STRING PROTEIN IS REQUIRED FOR CALCIUM SECRETION COUPLING OFEVOKED NEUROTRANSMISSION IN DROSOPHILA BUT NOT FOR VESICLE RECYCLING, The Journal of neuroscience, 18(3), 1998, pp. 956-964
The entire deletion of the cysteine string protein (CSP) gene causes a
temperature-sensitive (ts) block of evoked neurotransmission in Droso
phila. CSP has been found to interact in vitro with the clathrin-uncoa
ting ATPase HSC70, suggesting a potential role of CSP in vesicle recyc
ling. Using FM1-43 imaging, we analyzed whether the ts block of neurot
ransmission in csp mutants is caused by a defect in vesicle exocytosis
or vesicle recycling. We determined that FM1-43-labeled synaptic bout
ons of csp mutant neuromuscular junctions fail to destain at 32 degree
s C after K+ depolarization, and that FM1-43 dye uptake cannot be evok
ed by K+ stimulation at 32 degrees C. However, when we stimulated dye
uptake independent of depolarization by using black widow spider venom
(BWSV), we observed endocytotic uptake of FM1-43. This suggests that
endocytosis exhibits no primary ts defect. In addition, we found no ts
defect of vesicle recycling at 32 degrees C that would correlate with
the ts block of neurotransmission. We also discovered that BWSV and t
he calcium ionophore calcimycin stimulate FM1-43 destaining and quanta
l release in csp mutants at 32 degrees C when depolarization fails to
evoke any response. The wild-type-like, calcimycin-induced response in
csp null mutants indicates that some aspect of the depolarization-dep
endent calcium signaling pathway must be impaired, either calcium entr
y, calcium action, or both. Collectively, our results indicate that th
e csp mutation affects calcium secretion coupling of evoked exocytosis
but not vesicle recycling. This supports the hypothesis that CSP link
s synaptic vesicles to calcium secretion coupling.