Control of exocytosis by synaptotagmins and otoferlin in auditory hair cells.
Control of exocytosis by synaptotagmins and otoferlin in auditory hair cells.
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DOI：
10.1523/jneurosci.2528-10.2010
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发表时间：
2010-10-06
期刊：
影响因子：
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通讯作者：
Dulon D
中科院分区：
文献类型：
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作者：
Beurg M;Michalski N;Safieddine S;Bouleau Y;Schneggenburger R;Chapman ER;Petit C;Dulon D
在听前小鼠中，耳蜗内毛细胞（IHC）带状突触处的囊泡胞吐由自发性Ca 2+尖峰触发。在听力开始时，IHC胞吐作用然后完全由分级电位驱动，并且其特征在于更高的Ca 2+效率和囊泡释放的改善的同步。参与这一转变的分子参与者仍然是未知的。在这里，我们解决了参与synaptotagmins和otoferlin推定的Ca 2+传感器在IHC胞吐在出生后成熟的耳蜗。使用细胞电容测量，我们表明，钙离子诱发的胞吐在小鼠IHC开关从一个otoferlin独立的otoferlin依赖的机制在出生后第4天。在此早期胞吐期间，几个突触结合蛋白（Syts），包括Syt 1，Syt 2和Syt 7，检测到IHC。然而，在缺乏Syt 1、Syt 2或Syt 7的新生突变小鼠（Syt 1 −/−、Syt 2 −/−和Syt 7 −/−小鼠）中，胞吐反应以及易释放囊泡池（RRP）的释放没有变化。我们只在Syt 1 −/−小鼠中发现了RRP恢复的缺陷，这明显表现为对重复刺激的反应强烈减弱。在听力后Syt 2 −/−和Syt 7 −/−突变小鼠中，IHC突触胞吐不受影响。Syt 1和Syt 2的瞬时表达，这是不再检测到在IHC的听力发作后，表明这两个最常见的Ca 2 +-传感器在中枢神经系统突触不参与成熟的IHC。我们认为，otoferlin的基础是高效的Ca 2+依赖的膜-膜融合，这一过程可能是必不可少的，以增加在成熟的IHC带状突触囊泡融合事件的概率和同步性。
In pre-hearing mice, vesicle exocytosis at cochlear inner hair cell (IHC) ribbon synapses is triggered by spontaneous Ca2+ spikes. At the onset of hearing, IHC exocytosis is then exclusively driven by graded potentials, and is characterized by higher Ca2+ efficiency and improved synchronization of vesicular release. The molecular players involved in this transition are still unknown. Here we addressed the involvement of synaptotagmins and otoferlin as putative Ca2+ sensors in IHC exocytosis during postnatal maturation of the cochlea. Using cell capacitance measurements, we showed that Ca2+-evoked exocytosis in mouse IHCs switches from an otoferlin-independent to an otoferlin-dependent mechanism at postnatal day 4. During this early exocytotic period, several synaptotagmins (Syts), including Syt1, Syt2 and Syt7, were detected in IHCs. The exocytotic response as well as the release of the readily releasable vesicle pool (RRP) was, however, unchanged in newborn mutant mice lacking Syt1, Syt2 or Syt7 (Syt1−/−,Syt2−/− and Syt7−/− mice). We only found a defect in RRP recovery in Syt1−/− mice which was apparent as a strongly reduced response to repetitive stimulations. In post-hearing Syt2−/− and Syt7−/− mutant mice, IHC synaptic exocytosis was unaffected. The transient expression of Syt1 and Syt2, which were no longer detected in IHCs after the onset of hearing, indicates that these two most common Ca2+-sensors in CNS synapses are not involved in mature IHCs. We suggest that otoferlin underlies highly efficient Ca2+-dependent membrane-membrane fusion, a process likely essential to increase the probability and synchrony of vesicle fusion events at the mature IHC ribbon synapse.