Synaptic Ribbons Require Ribeye for Electron Density, Proper Synaptic Localization, and Recruitment of Calcium Channels

• Published in: Cell reports (Cambridge) Vol. 15; no. 12; pp. 2784 - 2795
• Main Authors: Lv, Caixia, Stewart, William J., Akanyeti, Otar, Frederick, Courtney, Zhu, Jie, Santos-Sacchi, Joseph, Sheets, Lavinia, Liao, James C., Zenisek, David
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21.06.2016; Elsevier
• Subjects: Animals; Calcium Channels - metabolism; Danio rerio; Electric Capacitance; Electrons; Exocytosis; Eye Proteins - metabolism; hair cell; Hair Cells, Auditory - metabolism; hearing; Homozygote; Ion Channel Gating; Mutation - genetics; Nerve Tissue Proteins - metabolism; Neurons, Afferent - metabolism; Patch-Clamp Techniques; Photoreceptor Cells, Vertebrate - metabolism; Photoreceptor Cells, Vertebrate - ultrastructure; retina; Synapses - metabolism; Synapses - ultrastructure; synaptic ribbon; vestibular system; Zebrafish - metabolism; Zebrafish Proteins - metabolism; hearing; exocytosis; retina; synaptic ribbon; hair cell; vestibular system
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2016.05.045

Synaptic ribbons are structures made largely of the protein Ribeye that hold synaptic vesicles near release sites in non-spiking cells in some sensory systems. Here, we introduce frameshift mutations in the two zebrafish genes encoding for Ribeye and thus remove Ribeye protein from neuromast hair cells. Despite Ribeye depletion, vesicles collect around ribbon-like structures that lack electron density, which we term “ghost ribbons.” Ghost ribbons are smaller in size but possess a similar number of smaller vesicles and are poorly localized to synapses and calcium channels. These hair cells exhibit enhanced exocytosis, as measured by capacitance, and recordings from afferent neurons post-synaptic to hair cells show no significant difference in spike rates. Our results suggest that Ribeye makes up most of the synaptic ribbon density in neuromast hair cells and is necessary for proper localization of calcium channels and synaptic ribbons. [Display omitted] •Ribeye is needed for electron density to form at hair cell synaptic ribbons•Ribeye mutants have smaller synaptic vesicles and mislocalized ribbons•Ribeye is required for synaptic ribbon association with calcium channels•Continuous exocytosis is enhanced in ribeye mutants despite ribbon mislocalization Synaptic ribbons are features of the auditory, vestibular, and visual systems that hold vesicles close to release sites in sensory cells. Lv et al. now find that genetic reduction of Ribeye levels in zebrafish results in the disruption of synaptic ribbon localization and morphology with minor effects on kinetics or levels of vesicle exocytosis.