Morphological and functional effects of altered cysteine string protein at the Drosophila larval neuromuscular junction |
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Authors: | Dawson-Scully Ken Lin Yongqi Imad Mays Zhang Jinhui Marin Leo Horne Jane A Meinertzhagen Ian A Karunanithi Shanker Zinsmaier Konrad E Atwood Harold L |
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Affiliation: | Department of Biology, University of Toronto, Mississauga, Ontario L5L 1C6, Canada. k.dawson.scully@utoronto.ca |
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Abstract: | The synaptic vesicle-associated cysteine string protein (CSP) is critical for neurotransmitter release at the neuromuscular junction (NMJ) of Drosophila, where the approximately 4% of mutant flies lacking CSP that survive to adulthood exhibit spastic jumping and shaking, temperature-sensitive paralysis, and premature death. Previously, it has been shown that CSP is also required for nerve terminal growth and the prevention of neurodegeneration in Drosophila and mice. At larval csp null mutant NMJs of Drosophila, intracellular recordings from the muscle showed that evoked release is significantly reduced at room temperature. However, it remained unclear whether the reduction in evoked release might be due to a loss of synaptic boutons, loss of synapses, and alterations in trafficking of vesicles to synapses. To resolve these issues, we have examined synaptic structure and function of csp null mutant NMJs at the level of single boutons. csp null mutations proportionally reduce the number of synaptic boutons of both motor neurons (1s and 1b) innervating larval muscles 6 and 7, while the number of synapses per bouton remains normal. However, focal recordings from individual synaptic boutons show that nerve-evoked neurotransmitter release is also impaired in both 1s and 1b boutons. Further, our ultrastructural analyses show that the reduction in evoked release at low stimulation frequencies is not due to a loss of synapses or to alterations in docked vesicles at synapses. Together, these data suggest that CSP promotes synaptic growth and evoked neurotransmitter release by mechanistically independent signaling pathways. |
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Keywords: | CSP synaptic vesicle Hsp70 synaptic vesicle reserve pool nerve terminal growth neurotransmitter release synaptic growth active zone vesicle trafficking |
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