Non-polarized distribution of synaptotagmin IV in neurons: evidence that synaptotagmin IV is not a synaptic vesicle protein.
Synaptotagmin IV (Syt IV) expression is regulated by neuronal development and by depolarization in the brain and in neuronal cell cultures. In cultures, immunocytochemical analysis has shown that Syt IV is localized at the Golgi and at the tips of growing neurites, but little was known about associations between Syt IV and vesicles or organelles [J. Neurochem. 74 (2000) 518]. In this study we performed an electron microscopic (EM) analysis of developing mouse neocortex to determine the exact localization of Syt IV in native mouse tissues. In neurons of layer II/III, Syt IV was found to be localized in the dendrites and axons, and at the Golgi in the cell body. Some Syt IV signals were clearly associated with vesicles and/or organelles, but EM and cell fractionation studies showed no Syt IV signals at synaptic vesicles. Detection of fluorescence protein-tagged Syt IV (Syt IV-EGFP) in hippocampal neurons also showed the presence of Syt IV-EGFP vesicles or organelles in the axons and dendrites. These results suggest that Syt IV regulates non-polarized membrane trafficking in neurons, which may be involved in synaptic plasticity or neuronal development.
Laboratory for Developmental Neurobiology, Brain Science Institute, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Keiji
K
Ibata
Tsutomu
T
Hashikawa
Takashi
T
Tsuboi
Susumu
S
Terakawa
Fengyi
F
Liang
Akihiro
A
Mizutani
Mitsunori
M
Fukuda
Katsuhiko
K
Mikoshiba
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D002135:Calcium-Binding Proteins; D002478:Cells, Cultured; D049452:Green Fluorescent Proteins; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D007150:Immunohistochemistry; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008854:Microscopy, Electron; D019579:Neocortex / Q000378:metabolism* / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism; D050857:Synaptotagmins; D014018:Tissue Distribution
D002135:Calcium-Binding Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C494293:Syt4 protein, mouse; D050857:Synaptotagmins; D049452:Green Fluorescent Proteins