Presynaptic dysfunction in drosophila csp mutants

Cysteine string proteins are synapse-specific proteins. In Drosophila, csp deletion mutants exhibit temperature-sensitive paralysis and early death. Here, we report that neuromuscular transmission is impaired presynaptically in these csp mutant larvae. At 22°C, evoked transmitter release is depressed relative to wild type and rescued controls, and high frequency stimulation of the nerve leads to sporadic failures. At 30°C, stimulus-evoked responses decline gradually before failing completely. When the temperature is returned to 22°C, evoked responses recover. Spontaneous release events persist at both 22°C and 30°C. Since nerve conduction and postsynaptic sensitivity are unaffected, these data indicate that csp mutations disrupt depolarization-secretion coupling. This disruption explains the cellular basis of the temperature-sensitive paralysis of these organisms.