A slowed classical pathway rather than kiss-and-run mediates endocytosis at synapses lacking synaptojanin and endophilin.
The extent to which a "kiss-and-run" mode of endocytosis contributes to synaptic-vesicle recycling remains controversial. The only genetic evidence for kiss-and-run at the synapse comes from mutations in the genes encoding synaptojanin and endophilin, proteins that together function to uncoat vesicles in classical clathrin-mediated endocytosis. Here we have characterized the endocytosis that persists in null alleles of Drosophila synaptojanin and endophilin. In response to high-frequency stimulation, the synaptic-vesicle pool can be reversibly depleted in these mutants. Recovery from this depletion is slow and indicates the persistence of an impaired form of classical endocytosis. Steady-state exocytosis rates reveal that endocytosis saturates in mutant neuromuscular terminals at approximately 80 vesicles/s, 10%-20% of the wild-type rate. Analyses of quantal size, FM1-43 loading, and dynamin function further demonstrate that, even in the absence of synaptojanin or endophilin, vesicles undergo full fusion and re-formation. Therefore, no genetic evidence remains to indicate that synaptic vesicles undergo kiss-and-run.
Dickman
Dion K
DK
Division of Neuroscience, Children,s Hospital and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Horne
Jane Anne
JA
Meinertzhagen
Ian A
IA
Schwarz
Thomas L
TL
D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D004330:Drosophila / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D034281:Dynamins / Q000378:metabolism; D004558:Electric Stimulation; D004705:Endocytosis / Q000502:physiology; D005456:Fluorescent Dyes; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000502:physiology; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D013572:Synaptic Vesicles / Q000502:physiology / Q000648:ultrastructure
D029721:Drosophila Proteins; C073804:FM1 43; D005456:Fluorescent Dyes; D009419:Nerve Tissue Proteins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D000217:Acyltransferases; C456023:endophilin A, Drosophila; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases; D034281:Dynamins