Genetic analysis of synaptotagmin-7 function in synaptic vesicle exocytosis.
Synaptotagmin-7 is a candidate Ca(2+) sensor for exocytosis that is at least partly localized to synapses. Similar to synaptotagmin-1, which functions as a Ca(2+) sensor for fast synaptic vesicle (SV) exocytosis, synaptotagmin-7 contains C(2)A and C(2)B domains that exhibit Ca(2+)-dependent phospholipid binding. However, synaptotagmin-7 cannot replace synaptotagmin-1 as a Ca(2+) sensor for fast SV exocytosis, raising questions about the physiological significance of its Ca(2+)-binding properties. Here, we examine how synaptotagmin-7 binds Ca(2+) and test whether this Ca(2+) binding regulates Ca(2+)-triggered SV exocytosis. We show that the synaptotagmin-7 C(2)A domain exhibits a Ca(2+)-binding mode similar to that of the synaptotagmin-1 C(2)A domain, suggesting that the synaptotagmin-1 and -7 C(2) domains generally employ comparable Ca(2+)-binding mechanisms. We then generated mutant mice that lack synaptotagmin-7 or contain point mutations inactivating Ca(2+) binding either to both C(2) domains of synaptotagmin-7 or only to its C(2)B domain. Synaptotagmin-7-mutant mice were viable and fertile. Inactivation of Ca(2+) binding to both C(2) domains caused an approximately 70% reduction in synaptotagmin-7 levels, whereas inactivation of Ca(2+) binding to only the C(2)B 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 Ca(2+) binding to the synaptotagmin-7 C(2) domains is physiologically important for stabilizing synaptotagmin-7, but that Ca(2+) binding by synaptotagmin-7 likely does not regulate SV exocytosis, consistent with a role for synaptotagmin-7 in other forms of Ca(2+)-dependent synaptic exocytosis.
Maximov
Anton
A
Departments of Neuroscience, Molecular Genetics, Pharmacology, and Biochemistry and Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, TX 75390-9111, USA.
Lao
Ye
Y
Li
Hongmei
H
Chen
Xiaocheng
X
Rizo
Josep
J
Sørensen
Jakob B
JB
Südhof
Thomas C
TC
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005089:Exocytosis; D018390:Gene Targeting; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D009154:Mutation / Q000235:genetics; D009474:Neurons / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D009435:Synaptic Transmission; D013572:Synaptic Vesicles / Q000378:metabolism*; D050863:Synaptotagmin I / Q000378:metabolism; D050857:Synaptotagmins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*
D050863:Synaptotagmin I; D050857:Synaptotagmins; D002118:Calcium