Distribution of proteins associated with synaptic vesicle endocytosis in the mouse and goldfish retina.
Current models of synaptic transmission require retrieval of membrane from the presynaptic terminal following neurotransmitter exocytosis. Dynamin, a GTPase, is thought to be critical for this retrieval process. At ribbon synapses of retinal bipolar neurons, however, compensatory endocytosis does not require GTP hydrolysis, suggesting that endocytosis mechanisms may differ among synapses. To understand better the synaptic vesicle recycling at conventional and ribbon synapses, the distributions of dynamin and two associated proteins, amphiphysin and clathrin, were examined in the retinas of goldfish and mouse by using immunocytochemical methods. Labeling for dynamin, clathrin, and amphiphysin was distributed differentially among conventional and ribbon synapses in retinas of both species. Ribbon synapses of photoreceptors and most bipolar cells labeled only weakly for dynamin relative to conventional synapses. Amphyiphysin labeling was strong at many ribbon synapses, and labeling in rod terminals was stronger than in cone terminals in the mouse retina. Clathrin labeling was heterogeneous among ribbon synapses. Similarly to the case with amphiphysin, mouse rod terminals showed stronger clathrin labeling than cone terminals. Among conventional synapses, there was heterogeneous labeling for all three endocytic proteins. Some labeling for each protein might have been associated with postsynaptic terminals. The differential distribution of labeling for these proteins among identified synapses in the retina suggests considerable heterogeneity in the molecular mechanisms underlying synaptic membrane retrieval, even among synapses with similar active zone ultrastructure. Thus, as with exocytosis, mechanisms of synaptic membrane retrieval may be tuned by the precise complement of proteins expressed within the synaptic terminal.
Sherry
David M
DM
University of Houston College of Optometry, Houston, Texas 77204-2020, USA. dsherry@uh.edu
Heidelberger
Ruth
R
D000818:Animals; D015153:Blotting, Western; D002966:Clathrin / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D006054:Goldfish; D007150:Immunohistochemistry; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D009435:Synaptic Transmission; D013572:Synaptic Vesicles / Q000378:metabolism*
D002966:Clathrin; D009419:Nerve Tissue Proteins; C075637:amphiphysin; D034281:Dynamins