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.

中文翻译：

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在 Usher 综合征 1 型斑马鱼模型中，L 型电压门控钙通道激动剂可减轻听力损失并改变带状突触形态。

水手( myo7aa ^-/- ) 突变体是 Usher 综合征 1 型 (USH1)的斑马鱼模型。为了进一步表征myo7aa ^-/-突变体中的毛细胞突触元件，我们专注于带状突触并评估免疫标记带的超微结构、数量和分布以及突触后密度。通过透射电子显微镜，我们确定myo7aa ^-/-斑马鱼与带状突触相连的谷氨酸能小泡较少，但仍保持相当的带状区域。在myo7aa ^-/-毛细胞中，与野生型毛细胞相比，Ctbp2 的免疫定位显示含带状细胞总数较少，Ctbp2 puncta 分布改变。与野生型斑马鱼相比，myo7aa ^{-/-突变体的突触后密度（通过 MAGUK 免疫标记评估）更少。}我们量化了myo7aa ^-/-突变鱼的圆形游泳行为，并测量了更大的转角（绝对平滑方向）。先前已经表明，L 型电压门控钙通道对于带状定位和突触后密度的发生是必需的。因此，我们假设并观察到 ​​L 型电压门控钙通道激动剂会改变myo7aa的行为和突触表型^-/-以药物特异性方式突变。我们的结果表明，用 L 型电压门控钙通道激动剂治疗会改变毛细胞突触元件并改善myo7aa ^-/-突变体的行为表型。我们的数据支持 L 型电压门控钙通道激动剂诱导带状突触的形态学变化——在栓系囊泡的数量和 Ctbp2 puncta 的分布方面——改变游泳行为并改善听觉惊吓反应。