title: Probing the functional equivalence of otoferlin and synaptotagmin 1 in exocytosis.
abstract: Cochlear inner hair cells (IHCs) use Ca(2+)-dependent exocytosis of glutamate to signal sound information. Otoferlin (Otof), a C(2) domain protein essential for IHC exocytosis and hearing, may serve as a Ca(2+) sensor in vesicle fusion in IHCs that seem to lack the classical neuronal Ca(2+) sensors synaptotagmin 1 (Syt1) and Syt2. Support for the Ca(2+) sensor of fusion hypothesis for otoferlin function comes from biochemical experiments, but additional roles in late exocytosis upstream of fusion have been indicated by physiological studies. Here, we tested the functional equivalence of otoferlin and Syt1 in three neurosecretory model systems: auditory IHCs, adrenal chromaffin cells, and hippocampal neurons. Long-term and short-term ectopic expression of Syt1 in IHCs of Otof (-/-) mice by viral gene transfer in the embryonic inner ear and organotypic culture failed to rescue their Ca(2+) influx-triggered exocytosis. Conversely, virally mediated overexpression of otoferlin did not restore phasic exocytosis in Syt1-deficient chromaffin cells or neurons but enhanced asynchronous release in the latter. We further tested exocytosis in Otof (-/-) hippocampal neurons and in Syt1(-/-) IHCs but found no deficits in vesicle fusion. Expression analysis of different synaptotagmin isoforms indicated that Syt1 and Syt2 are absent from mature IHCs. Our data argue against a simple functional equivalence of the two C(2) domain proteins in exocytosis of IHC ribbon synapses, chromaffin cells, and hippocampal synapses.
authors: Molecular Biology of Cochlear Neurotransmission, Department of Otolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany.
authors: Ellen
authors: E
authors: Reisinger
authors: Chris
authors: C
authors: Bresee
authors: Jakob
authors: J
authors: Neef
authors: Ramya
authors: R
authors: Nair
authors: Kirsten
authors: K
authors: Reuter
authors: Anna
authors: A
authors: Bulankina
authors: Régis
authors: R
authors: Nouvian
authors: Manuel
authors: M
authors: Koch
authors: Johanna
authors: J
authors: Bückers
authors: Lars
authors: L
authors: Kastrup
authors: Isabelle
authors: I
authors: Roux
authors: Christine
authors: C
authors: Petit
authors: Stefan W
authors: SW
authors: Hell
authors: Nils
authors: N
authors: Brose
authors: Jeong-Seop
authors: JS
authors: Rhee
authors: Sebastian
authors: S
authors: Kügler
authors: John V
authors: JV
authors: Brigande
authors: Tobias
authors: T
authors: Moser
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000818:Animals; D000831:Animals, Newborn; D016057:Evoked Potentials, Auditory, Brain Stem / Q000235:genetics / Q000502:physiology; D005089:Exocytosis / Q000235:genetics / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology / Q000502:physiology; D008561:Membrane Fusion / Q000235:genetics; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051379:Mice; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D009433:Neural Inhibition / Q000235:genetics; D009474:Neurons / Q000378:metabolism; D009924:Organ Culture Techniques; D013569:Synapses / Q000235:genetics / Q000502:physiology; D050863:Synaptotagmin I / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
chemical_list: D008565:Membrane Proteins; D050863:Synaptotagmin I; C516233:otoferlin protein, mouse