Synaptotagmin VII restricts fusion pore expansion during lysosomal exocytosis.
Synaptotagmin is considered a calcium-dependent trigger for regulated exocytosis. We examined the role of synaptotagmin VII (Syt VII) in the calcium-dependent exocytosis of individual lysosomes in wild-type (WT) and Syt VII knockout (KO) mouse embryonic fibroblasts (MEFs) using total internal reflection fluorescence microscopy. In WT MEFs, most lysosomes only partially released their contents, their membrane proteins did not diffuse into the plasma membrane, and inner diameters of their fusion pores were smaller than 30 nm. In Syt VII KO MEFs, not only was lysosomal exocytosis triggered by calcium, but all of these restrictions on fusion were also removed. These observations indicate that Syt VII does not function as the calcium-dependent trigger for lysosomal exocytosis. Instead, it restricts the kinetics and extent of calcium-dependent lysosomal fusion.
Jaiswal
Jyoti K
JK
Department of Cellular Biophysics, Rockefeller University, New York, New York, USA.
Chakrabarti
Sabyasachi
S
Andrews
Norma W
NW
Simon
Sanford M
SM
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D005089:Exocytosis; D005347:Fibroblasts / Q000166:cytology; D007091:Image Processing, Computer-Assisted; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D051907:Lysosomal Membrane Proteins / Q000737:chemistry; D008247:Lysosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D009419:Nerve Tissue Proteins / Q000737:chemistry; D050857:Synaptotagmins / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors
D007476:Ionophores; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D050857:Synaptotagmins; D002118:Calcium