Journal of Cell Science 116, e104-e104 (2003)
Copyright © 2003 The Company of Biologists Limited
A trafficking role for synaptotagmin III
Among the numerous different protein families implicated in control of
membrane trafficking are the synaptotagmins. These are large integral membrane
proteins that bind to phospholipids and the t-SNAREs syntaxins. Synaptotagmin
I and synaptotagmin II are thought to function in neurotransmitter release and
lysosomal exocytosis, respectively, but precious little is known about what
the other 11 members of this family do. Ronit Sagi-Eisenberg and co-workers
have now studied the role of synaptotagmin III, which is expressed in mast
cells (see p. 145).
Colocalizing the protein with markers proteins such as EEA1 and histamine,
they show that it is present on early endosomes and secretory granules. They
then use an antisense cDNA approach to reduce synaptotagmin III levels:
although this has no effect on uptake of cargo (transferrin) into early
endosomes, it does block transport from early endosomes to the perinuclear
endocytic recycling compartment (ERC) and also generates enlarged secretory
granules. The authors therefore conclude that synaptotagmin III is critical
for transport of cargo from early endosomes to the ERC. Furthermore, given the
effect on secretory granules, they suggest it is part of a novel mechanism for
recycling of material from immature secretory granules to the ERC during their
maturation.
Related articles in JCS:
- Synaptotagmin III is a critical factor for the formation of the perinuclear endocytic recycling compartment and determination of secretory granules size
- Elena Grimberg, Ze Peng, Ilan Hammel, and Ronit Sagi-Eisenberg
JCS 2003 116: 145-154.
[Abstract]
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