Department of Biochemistry, Faculty of Medicine, University of Yamanashi, Yamanashi, Japan.
Department of Pharmacology, Kurume University School of Medicine, Fukuoka, Japan.
J Cell Biol. 2018 Nov 5;217(11):3993-4006. doi: 10.1083/jcb.201704076. Epub 2018 Sep 6.
At the presynaptic active zone (AZ), the related cytomatrix proteins CAST and ELKS organize the presynaptic release machinery. While CAST is known to regulate AZ size and neurotransmitter release, the role of ELKS and the integral system of CAST/ELKS together is poorly understood. Here, we show that CAST and ELKS have both redundant and unique roles in coordinating synaptic development, function, and maintenance of retinal photoreceptor ribbon synapses. A CAST/ELKS double knockout (dKO) mouse showed high levels of ectopic synapses and reduced responses to visual stimulation. Ectopic formation was not observed in ELKS conditional KO but progressively increased with age in CAST KO mice with higher rates in the dKO. Presynaptic calcium influx was strongly reduced in rod photoreceptors of CAST KO and dKO mice. Three-dimensional scanning EM reconstructions showed structural abnormalities in rod triads of CAST KO and dKO. Remarkably, AAV-mediated acute ELKS deletion after synapse maturation induced neurodegeneration and loss of ribbon synapses. These results suggest that CAST and ELKS work in concert to promote retinal synapse formation, transmission, and maintenance.
在突触前活性区 (AZ)，相关的细胞基质蛋白 CAST 和 ELKS 组织了突触前释放机制。虽然 CAST 已知可以调节 AZ 的大小和神经递质的释放，但 ELKS 的作用以及 CAST/ELKS 的整体系统的作用还知之甚少。在这里，我们表明 CAST 和 ELKS 在协调视网膜光感受器 ribbon 突触的突触发育、功能和维持方面都具有冗余和独特的作用。CAST/ELKS 双敲除 (dKO) 小鼠表现出高水平的异位突触和对视觉刺激的反应减少。ELKS 条件性 KO 中没有观察到异位形成，但在 CAST KO 小鼠中随年龄逐渐增加，dKO 中的比率更高。CAST KO 和 dKO 小鼠的 rod 光感受器中的钙内流明显减少。三维扫描 EM 重建显示 CAST KO 和 dKO 中的 rod 三联体存在结构异常。值得注意的是，突触成熟后通过 AAV 介导的急性 ELKS 删除会诱导神经退行性变和 ribbon 突触的丧失。这些结果表明 CAST 和 ELKS 协同作用以促进视网膜突触的形成、传递和维持。
