title: The SNARE protein vti1a functions in dense-core vesicle biogenesis.
abstract: The SNARE protein vti1a is proposed to drive fusion of intracellular organelles, but recent data also implicated vti1a in exocytosis. Here we show that vti1a is absent from mature secretory vesicles in adrenal chromaffin cells, but localizes to a compartment near the trans-Golgi network, partially overlapping with syntaxin-6. Exocytosis is impaired in vti1a null cells, partly due to fewer Ca(2+)-channels at the plasma membrane, partly due to fewer vesicles of reduced size and synaptobrevin-2 content. In contrast, release kinetics and Ca(2+)-sensitivity remain unchanged, indicating that the final fusion reaction leading to transmitter release is unperturbed. Additional deletion of the closest related SNARE, vti1b, does not exacerbate the vti1a phenotype, and vti1b null cells show no secretion defects, indicating that vti1b does not participate in exocytosis. Long-term re-expression of vti1a (days) was necessary for restoration of secretory capacity, whereas strong short-term expression (hours) was ineffective, consistent with vti1a involvement in an upstream step related to vesicle generation, rather than in fusion. We conclude that vti1a functions in vesicle generation and Ca(2+)-channel trafficking, but is dispensable for transmitter release.
authors.affiliation: Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark Department of Functional Genomics and Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, Amsterdam, The Netherlands.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Walter
authors.affiliation: Department of Functional Genomics and Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, Amsterdam, The Netherlands.
authors.forename: Julia
authors.initials: J
authors.lastname: Kurps
authors.affiliation: Department of Functional Genomics and Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, Amsterdam, The Netherlands.
authors.forename: Heidi
authors.initials: H
authors.lastname: de Wit
authors.affiliation: Biochemie III, Fakultät für Chemie, Universität Bielefeld, Bielefeld, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Schöning
authors.affiliation: Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Trine L
authors.initials: TL
authors.lastname: Toft-Bertelsen
authors.affiliation: Department of Functional Genomics and Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, Amsterdam, The Netherlands.
authors.forename: Juliane
authors.initials: J
authors.lastname: Lauks
authors.affiliation: Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Iwona
authors.initials: I
authors.lastname: Ziomkiewicz
authors.affiliation: Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Annita N
authors.initials: AN
authors.lastname: Weiss
authors.affiliation: Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Alexander
authors.initials: A
authors.lastname: Schulz
authors.affiliation: Biochemie III, Fakultät für Chemie, Universität Bielefeld, Bielefeld, Germany.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Fischer von Mollard
authors.affiliation: Department of Functional Genomics and Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, Amsterdam, The Netherlands.
authors.forename: Matthijs
authors.initials: M
authors.lastname: Verhage
authors.affiliation: Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark jakobbs@sund.ku.dk.
authors.forename: Jakob B
authors.initials: JB
authors.lastname: Sørensen
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D022003:Cell Nucleus Structures / Q000378:metabolism; D019439:Chromaffin Cells / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D050765:Qa-SNARE Proteins / Q000378:metabolism; D050766:Qb-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050988:Vesicle-Associated Membrane Protein 2; C491418:Vti1a protein, mouse; C491415:Vti1b protein, mouse
keywords: Ca2+‐channels; SNARE; adrenal chromaffin cells; exocytosis; vesicle biogenesis