Otoferlin acts as a Ca 2+ sensor for vesicle fusion and vesicle pool replenishment at auditory hair cell ribbon synapses

Elife. 2017 Nov 7;6:e31013. doi: 10.7554/eLife.31013.

Abstract

Hearing relies on rapid, temporally precise, and sustained neurotransmitter release at the ribbon synapses of sensory cells, the inner hair cells (IHCs). This process requires otoferlin, a six C2-domain, Ca2+-binding transmembrane protein of synaptic vesicles. To decipher the role of otoferlin in the synaptic vesicle cycle, we produced knock-in mice (OtofAla515,Ala517/Ala515,Ala517) with lower Ca2+-binding affinity of the C2C domain. The IHC ribbon synapse structure, synaptic Ca2+ currents, and otoferlin distribution were unaffected in these mutant mice, but auditory brainstem response wave-I amplitude was reduced. Lower Ca2+ sensitivity and delay of the fast and sustained components of synaptic exocytosis were revealed by membrane capacitance measurement upon modulations of intracellular Ca2+ concentration, by varying Ca2+ influx through voltage-gated Ca2+-channels or Ca2+ uncaging. Otoferlin thus functions as a Ca2+ sensor, setting the rates of primed vesicle fusion with the presynaptic plasma membrane and synaptic vesicle pool replenishment in the IHC active zone.

Keywords: deafness; inner hair cell; mouse; neuroscience; neurotransmitter release; synaptic exocytotic machinery; synaptopathy; temporal precision.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Gene Knock-In Techniques
  • Hair Cells, Auditory / physiology*
  • Membrane Fusion*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Protein Binding
  • Receptors, Calcium-Sensing / genetics
  • Receptors, Calcium-Sensing / metabolism*
  • Synapses / physiology*
  • Synaptic Vesicles / metabolism*

Substances

  • Membrane Proteins
  • Receptors, Calcium-Sensing
  • otoferlin protein, mouse
  • Calcium