Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, IA, 52242, USA.
Key Laboratory of Medical Electrophysiology of Ministry of Education, Medical Electrophysiological Key Lab of Sichuan Province, Institute of Cardiovascular Research of Southwest Medical University, Luzhou, 646000, China.
J Physiol. 2020 Jun;598(12):2431-2452. doi: 10.1113/JP279736. Epub 2020 May 19.
CAST/ELKS are positive regulators of presynaptic growth and are suppressors of active zone expansion at the developing mouse calyx of Held. CAST/ELKS regulate all three Ca 2 subtype channel levels in the presynaptic terminal and not just Ca 2.1. The half-life of ELKS is on the timescale of days and not weeks. Synaptic transmission was not impacted by the loss of CAST/ELKS. CAST/ELKS are involved in pathways regulating morphological properties of presynaptic terminals during an early stage of circuit maturation.
Many presynaptic active zone (AZ) proteins have multiple regulatory roles that vary during distinct stages of neuronal circuit development. The CAST/ELKS protein family are evolutionarily conserved presynaptic AZ molecules that regulate presynaptic calcium channels, synaptic transmission and plasticity in the mammalian CNS. However, how these proteins regulate synapse development and presynaptic function in a developing neuronal circuit in its native environment is unclear. To unravel the roles of CAST/ELKS in glutamatergic synapse development and in presynaptic function, we used CAST knockout (KO) and ELKS conditional KO (CKO) mice to examine how their loss during the early stages of circuit maturation impacted the calyx of Held presynaptic terminal development and function. Morphological analysis from confocal z-stacks revealed that combined deletion of CAST/ELKS resulted in a reduction in the surface area and volume of the calyx. Analysis of AZ ultrastructure showed that AZ size was increased in the absence of CAST/ELKS. Patch clamp recordings demonstrated a reduction of all presynaptic Ca 2 channel subtype currents that correlated with a loss in presynaptic Ca 2 channel numbers. However, these changes did not impair synaptic transmission and plasticity and synaptic vesicle release kinetics. We conclude that CAST/ELKS proteins are positive regulators of presynaptic growth and are suppressors of AZ expansion and Ca 2 subtype currents and levels during calyx of Held development. We propose that CAST/ELKS are involved in pathways regulating presynaptic morphological properties and Ca 2 channel subtypes and suggest there is developmental compensation to preserve synaptic transmission during early stages of neuronal circuit maturation.
CAST/ELKS 是突触前生长的正调控因子，也是发育中的小鼠耳石突触前囊中活性区扩张的抑制剂。CAST/ELKS 调节突触前末梢中所有三种 Ca 2 亚型通道的水平，而不仅仅是 Ca 2.1。ELKS 的半衰期在数天的时间尺度上，而不是数周。突触传递不受 CAST/ELKS 缺失的影响。CAST/ELKS 参与调节突触前末梢形态特性的途径，在神经元回路成熟的早期阶段。
许多突触前活性区 (AZ) 蛋白具有多种调节作用，这些作用在神经元回路发育的不同阶段有所不同。CAST/ELKS 蛋白家族是进化上保守的突触前 AZ 分子，调节哺乳动物中枢神经系统中的突触前钙通道、突触传递和可塑性。然而，这些蛋白如何在其天然环境中调节发育中的神经元回路中突触的发育和突触前功能尚不清楚。为了揭示 CAST/ELKS 在谷氨酸能突触发育和突触前功能中的作用，我们使用 CAST 敲除 (KO) 和 ELKS 条件性敲除 (CKO) 小鼠来研究它们在回路成熟的早期阶段缺失如何影响耳石突触前末梢的发育和功能。共聚焦 z 堆栈的形态分析显示，CAST/ELKS 的联合缺失导致耳石表面积和体积减小。AZ 超微结构分析显示，在缺乏 CAST/ELKS 的情况下，AZ 大小增加。膜片钳记录显示所有突触前 Ca 2 通道亚型电流减少，与突触前 Ca 2 通道数量减少相关。然而，这些变化并没有损害突触传递和可塑性以及突触囊泡释放动力学。我们得出结论，CAST/ELKS 蛋白是突触前生长的正调控因子，是耳石发育过程中 AZ 扩张和 Ca 2 亚型电流和水平的抑制剂。我们提出 CAST/ELKS 参与调节突触前形态特性和 Ca 2 通道亚型的途径，并表明在神经元回路成熟的早期阶段存在发育补偿以维持突触传递。
