TY - JOUR
T1 - Genetic analysis of synaptotagmin-7 function in synaptic vesicle exocytosis
AU - Maximov, Anton
AU - Lao, Ye
AU - Li, Hongmei
AU - Chen, Xiaocheng
AU - Rizo-Rey, Jose
AU - Sørensen, Jakob B.
AU - Südhof, Thomas C.
PY - 2008/3/25
Y1 - 2008/3/25
N2 - Synaptotagmin-7 is a candidate Ca2+ sensor for exocytosis that is at least partly localized to synapses. Similar to synaptotagmin-1, which functions as a Ca2+ sensor for fast synaptic vesicle (SV) exocytosis, synaptotagmin-7 contains C2A and C2B domains that exhibit Ca2+-dependent phospholipid binding. However, synaptotagmin-7 cannot replace synaptotagmin-1 as a Ca2+ sensor for fast SV exocytosis, raising questions about the physiological significance of its Ca 2+-binding properties. Here, we examine how synaptotagmin-7 binds Ca2+ and test whether this Ca2+ binding regulates Ca 2+-triggered SV exocytosis. We show that the synaptotagmin-7 C 2A domain exhibits a Ca2+-binding mode similar to that of the synaptotagmin-1 C2A domain, suggesting that the synaptotagmin-1 and -7 C2 domains generally employ comparable Ca2+-binding mechanisms. We then generated mutant mice that lack synaptotagmin-7 or contain point mutations inactivating Ca2+ binding either to both C 2 domains of synaptotagmin-7 or only to its C2B domain. Synaptotagmin-7-mutant mice were viable and fertile. Inactivation of Ca 2+ binding to both C2 domains caused an ≈70% reduction in synaptotagmin-7 levels, whereas inactivation of Ca2+ binding to only the C2B domain did not alter synaptotagmin-7 levels. The synaptotagmin-7 deletion did not change fast synchronous release, slow asynchronous release, or short-term synaptic plasticity of release of neurotransmitters. Thus, our results show that Ca2+ binding to the synaptotagmin-7 C2 domains is physiologically important for stabilizing synaptotagmin-7, but that Ca2+ binding by synaptotagmin-7 likely does not regulate SV exocytosis, consistent with a role for synaptotagmin-7 in other forms of Ca2+-dependent synaptic exocytosis.
AB - Synaptotagmin-7 is a candidate Ca2+ sensor for exocytosis that is at least partly localized to synapses. Similar to synaptotagmin-1, which functions as a Ca2+ sensor for fast synaptic vesicle (SV) exocytosis, synaptotagmin-7 contains C2A and C2B domains that exhibit Ca2+-dependent phospholipid binding. However, synaptotagmin-7 cannot replace synaptotagmin-1 as a Ca2+ sensor for fast SV exocytosis, raising questions about the physiological significance of its Ca 2+-binding properties. Here, we examine how synaptotagmin-7 binds Ca2+ and test whether this Ca2+ binding regulates Ca 2+-triggered SV exocytosis. We show that the synaptotagmin-7 C 2A domain exhibits a Ca2+-binding mode similar to that of the synaptotagmin-1 C2A domain, suggesting that the synaptotagmin-1 and -7 C2 domains generally employ comparable Ca2+-binding mechanisms. We then generated mutant mice that lack synaptotagmin-7 or contain point mutations inactivating Ca2+ binding either to both C 2 domains of synaptotagmin-7 or only to its C2B domain. Synaptotagmin-7-mutant mice were viable and fertile. Inactivation of Ca 2+ binding to both C2 domains caused an ≈70% reduction in synaptotagmin-7 levels, whereas inactivation of Ca2+ binding to only the C2B domain did not alter synaptotagmin-7 levels. The synaptotagmin-7 deletion did not change fast synchronous release, slow asynchronous release, or short-term synaptic plasticity of release of neurotransmitters. Thus, our results show that Ca2+ binding to the synaptotagmin-7 C2 domains is physiologically important for stabilizing synaptotagmin-7, but that Ca2+ binding by synaptotagmin-7 likely does not regulate SV exocytosis, consistent with a role for synaptotagmin-7 in other forms of Ca2+-dependent synaptic exocytosis.
KW - Asynchronous release
KW - Calcium-binding protein
KW - Neurotransmitter release
KW - Synaptic plasticity
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U2 - 10.1073/pnas.0712372105
DO - 10.1073/pnas.0712372105
M3 - Article
C2 - 18308933
AN - SCOPUS:41649087823
SN - 0027-8424
VL - 105
SP - 3986
EP - 3991
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 10
ER -