Department of Food Science and Human Nutrition, Iowa State University, Ames, IA, USA.
Department of Cell Biology and Program in Neuroscience, Blavatnik Institute, Harvard Medical School, Boston, MA, USA.
Neural Dev. 2020 Mar 17;15(1):4. doi: 10.1186/s13064-020-00141-x.
Recent studies of synapse form and function highlight the importance of the actin cytoskeleton in regulating multiple aspects of morphogenesis, neurotransmission, and neural plasticity. The conserved actin-associated protein Enabled (Ena) is known to regulate development of the Drosophila larval neuromuscular junction through a postsynaptic mechanism. However, the functions and regulation of Ena within the presynaptic terminal has not been determined.
Here, we use a conditional genetic approach to address a presynaptic role for Ena on presynaptic morphology and ultrastructure, and also examine the pathway in which Ena functions through epistasis experiments.
We find that Ena is required to promote the morphogenesis of presynaptic boutons and branches, in contrast to its inhibitory role in muscle. Moreover, while postsynaptic Ena is regulated by microRNA-mediated mechanisms, presynaptic Ena relays the output of the highly conserved receptor protein tyrosine phosphatase Dlar and associated proteins including the heparan sulfate proteoglycan Syndecan, and the non-receptor Abelson tyrosine kinase to regulate addition of presynaptic varicosities. Interestingly, Ena also influences active zones, where it restricts active zone size, regulates the recruitment of synaptic vesicles, and controls the amplitude and frequency of spontaneous glutamate release.
We thus show that Ena, under control of the Dlar pathway, is required for presynaptic terminal morphogenesis and bouton addition and that Ena has active zone and neurotransmission phenotypes. Notably, in contrast to Dlar, Ena appears to integrate multiple pathways that regulate synapse form and function.
最近对突触形态和功能的研究强调了细胞骨架在调节形态发生、神经传递和神经可塑性的多个方面的重要性。保守的肌动蛋白相关蛋白 Enabled（Ena）已知通过突触后机制调节果蝇幼虫神经肌肉接头的发育。然而，Ena 在突触前末梢中的功能和调节尚未确定。
在这里，我们使用条件遗传方法来确定 Ena 在突触前形态和超微结构上的突触前作用，并通过上位实验检查 Ena 作用的途径。
我们发现 Ena 需要促进突触前末梢和分支的形态发生，这与它在肌肉中的抑制作用形成对比。此外，虽然突触后 Ena 受 microRNA 介导的机制调节，但突触前 Ena 传递高度保守的受体蛋白酪氨酸磷酸酶 Dlar 的输出以及相关蛋白，包括硫酸乙酰肝素蛋白聚糖 Syndecan 和非受体 Abelson 酪氨酸激酶，以调节突触前囊泡的添加。有趣的是，Ena 还影响活性区，在那里它限制活性区的大小，调节突触小泡的募集，并控制自发谷氨酸释放的幅度和频率。
因此，我们表明，在 Dlar 途径的控制下，Ena 是突触前末梢形态发生和末梢添加所必需的，并且 Ena 具有活性区和神经传递表型。值得注意的是，与 Dlar 不同，Ena 似乎整合了调节突触形态和功能的多个途径。
