The mariner (myo7aa−/−) mutant is a zebrafish model for Usher syndrome type 1 (USH1). To further characterize hair cell synaptic elements in myo7aa−/− mutants, we focused on the ribbon synapse and evaluated ultrastructure, number and distribution of immunolabeled ribbons, and postsynaptic densities. By transmission electron microscopy, we determined that myo7aa−/− zebrafish have fewer glutamatergic vesicles tethered to ribbon synapses, yet maintain a comparable ribbon area. In myo7aa−/− hair cells, immunolocalization of Ctbp2 showed fewer ribbon-containing cells in total and an altered distribution of Ctbp2 puncta compared to wild-type hair cells. myo7aa−/− mutants have fewer postsynaptic densities - as assessed by MAGUK immunolabeling - compared to wild-type zebrafish. We quantified the circular swimming behavior of myo7aa−/− mutant fish and measured a greater turning angle (absolute smooth orientation). It has previously been shown that L-type voltage-gated calcium channels are necessary for ribbon localization and occurrence of postsynaptic density; thus, we hypothesized and observed that L-type voltage-gated calcium channel agonists change behavioral and synaptic phenotypes in myo7aa−/− mutants in a drug-specific manner. Our results indicate that treatment with L-type voltage-gated calcium channel agonists alter hair cell synaptic elements and improve behavioral phenotypes of myo7aa−/− mutants. Our data support that L-type voltage-gated calcium channel agonists induce morphological changes at the ribbon synapse - in both the number of tethered vesicles and regarding the distribution of Ctbp2 puncta - shift swimming behavior and improve acoustic startle response.
Bibliographical noteFunding Information:
We thank Dr Teresa Nicolson for providing us with the tc320b allele of mariner. We are grateful to Mark Curry and Patrick Jochim in the Mayo Clinic Media Services. We also thank Dr Gabriel Martinez Galvez and Dr Timothy Wiggins for help with Adobe Illustrator, MATLAB and the behavior assessment. We are also grateful to Dr Lavinia Sheets for her helpful discussions. Last, we thank the staff members in the zebrafish core facilities at Mayo Clinic and the University of Minnesota, Twin Cities. A.K. was supported by the National Center for Advancing Translational Sciences (NCATS; grant number: UL1 TR000135), a component of the National Institutes of Health (NIH). M.A.M was supported by the NIH (grant number: R01NS094176). L.A.S. was supported by funding from the Mayo Clinic Center for Individualized Medicine, Philanthropic support from the Nelson Family Fund and from the Mayo Clinic Department of Otorhinolaryngology.
A.K. was supported by the National Center for Advancing Translational Sciences (NCATS; grant number: UL1 TR000135), a component of the National Institutes of Health (NIH). M.A.M was supported by the NIH (grant number: R01NS094176). L.A.S. was supported by funding from the Mayo Clinic Center for Individualized Medicine, Philanthropic support from the Nelson Family Fund and from the Mayo Clinic Department of Otorhinolaryngology.
© 2020 Company of Biologists Ltd. All rights reserved.
- Hair cell
- Hearing loss
- Ribbon synapse
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural
- Research Support, Non-U.S. Gov't