The dual phosphatase activity of synaptojanin1 is required for both efficient synaptic vesicle endocytosis and reavailability at nerve terminals.
Phosphoinositides have been implicated in synaptic vesicle recycling largely based on studies of enzymes that regulate phosphoinositide synthesis and hydrolysis. One such enzyme is synaptojanin1, a multifunctional protein conserved from yeast to humans, which contains two phosphoinositol phosphatase domains and a proline-rich domain. Genetic ablation of synaptojanin1 leads to pleiotropic defects in presynaptic function, including accumulation of free clathrin-coated vesicles and delayed vesicle reavailability, implicating this enzyme in postendocytic uncoating of vesicles. To further elucidate the role of synaptojanin1 at nerve terminals, we performed quantitative synaptic vesicle recycling assays in synj1(-/-) neurons. Our studies show that synaptojanin1 is also required for normal vesicle endocytosis. Defects in both endocytosis and postendocytic vesicle reavailability can be fully restored upon reintroduction of synaptojanin1. However, expression of synaptojanin1 with mutations abolishing catalytic activity of each phosphatase domain reveals that the dual action of both domains is required for normal synaptic vesicle internalization and reavailability.
Mani
Meera
M
Department of Biochemistry, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA.
Lee
Sang Yoon
SY
Lucast
Louise
L
Cremona
Ottavio
O
Di Paolo
Gilbert
G
De Camilli
Pietro
P
Ryan
Timothy A
TA
D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D004558:Electric Stimulation / Q000379:methods; D004705:Endocytosis / Q000502:physiology* / Q000528:radiation effects; D051379:Mice; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000378:metabolism*; D009474:Neurons / Q000166:cytology* / Q000528:radiation effects; D010744:Phosphoric Monoester Hydrolases / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology*; D011392:Proline / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013572:Synaptic Vesicles / Q000502:physiology* / Q000528:radiation effects; D013997:Time Factors; D014162:Transfection; D018909:src Homology Domains / Q000502:physiology
D009419:Nerve Tissue Proteins; D011392:Proline; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases