Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Poster Abstracts

49-POS Board 17 SYNAPTOTAGMIN-7 SPLICE VARIANTS ARE DIFFERENTLY INVOLVED IN DENSE-CORE VESICLE SECRETION IN MOUSE CHROMAFFIN CELLS

Joana Martins 1 ; Sebastien Houy 1 ; Mário Carvalho 1 ; Ralf Mohrmann 2 ; Jakob Sørensen 1 ; 1 University of Copenhagen, Department of Neuroscience, København, Denmark 2 Otto-von-Guericke Universität, Institute of Physiology, Magdeburg, Germany

Synaptotagmin-7 (Syt-7) is one of the main calcium sensors for large dense-core vesicle fusion in adrenal chromaffin cells, and it is involved in facilitation in central neurons. This protein consists of a single transmembrane domain and two Ca 2+ and phospholipid-binding C2 domains, C2A and C2B, separated by a linker region. This linker is alternatively spliced in several isoforms of Syt-7. Two splice variants are expressed in mouse chromaffin cells: synaptotagmin 7β (Syt - 7β) and the more abundant shorter isoform synaptotagmin- 7α (Syt - 7α). Syt - 7β differs by having an insertion of 44 amino acids within the linker region. We report that Syt- 7β supports a larger primed pool and more total secretion than Syt- 7α. We verified this by performing electrophysiological measurements on adrenal chromaffin cells from Syt-7 knockout mice virally expressing Syt- 7α and Syt - 7β. These differences cannot be explained by changes in linker size or calcium-dependence of secretion. Nevertheless, we observed that the Syt- 7β -mediated increase in secretion is sensitive to the inhibition of protein kinases. Indeed, the alternatively spliced linker region contains putative phosphorylation sites. These data indicate that vesicle priming/unpriming may be regulated by the alternative splicing of Syt-7, and that this process may depend on the phosphorylation of Syt-7 linker region.

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