Trans-synaptic coupling of phosphorylation signalling for central synapse development

正常的脑功能依赖于神经递质的兴奋性或抑制性物质在神经元之间的传递，这些物质位于称为突触的特殊粘附结构中。兴奋性突触在结构上是不对称的，神经递质从一侧（突触前侧）释放，在另一侧（突触后侧）接收，从而实现单向信息交流。这种不对称突触的发展需要突触两侧之间的粘附，然后是两侧不同但协调的蛋白质积累。需要许多蛋白质来驱动突触前和突触后的特化。特别是，一些可以通过磷酸化过程修饰其他蛋白质的蛋白质存在于发育中的突触的一侧或另一侧。为了协调突触组装，参与磷酸化的突触前蛋白和突触后蛋白的作用必须通过突触间隙连接起来。在这里，我们提出了一个新的研究计划，通过研究跨突触偶联磷酸化途径来揭示兴奋性突触结构和功能不对称的分子机制。

Normal brain function relies on the transfer of excitatory or inhibitory substances called neurotransmitters between neurons at specialized adhesion structures called synapses. Excitatory synapses are structurally asymmetric with neurotransmitter released from one side (the presynaptic side) and received at the other (the postsynaptic side), enabling uni-directional information communication. The development of such asymmetric synapses requires adhesion between the two sides of the synapse followed by differential but coordinated accumulation of proteins on either side. Many proteins are needed to drive this pre- and post-synaptic specialization. In particular, several proteins that can modify other proteins through a process called phosphorylation are present on one side or the other of the developing synapse. In order to coordinate synapse assembly, the actions of the pre- and post-synaptic proteins involved in phosphorylation must be linked across the synaptic cleft. Here we propose to develop a new research program to uncover molecular mechanisms underlying structural and functional asymmetry of excitatory synapses by investigating trans-synaptically-coupled phosphorylation pathways. Based on our preliminary data, we will focus on the actions of one particular protein pair: TrkC-PTP. TrkC is present post-synaptically and is a kinase that can phosphorylate other proteins. TrkC binds to PTP which is present pre-synaptically and can de-phosphorylate substrates. This protein interaction promotes formation of excitatory synapses but it is not known through which phosphorylation signalling pathways this occurs. Using genetically modified mice in which TrkC and PTP interaction is abolished and advanced techniques in molecular and cellular biology and biochemistry, we will identify the signalling pathways invoked by the TrkC-PTP complex at synapses and then examine how manipulation of these pathways alters synapse formation and function. We will also use the genetically modified mice to investigate how TrkC-PTP interaction is involved in synapse development in a whole-organism setting. This program will test a novel concept in synapse development: how coordinated trans-synaptic phosphorylation drives synapse asymmetry. Also, because some of the proteins that we will study are also involved in other tissues, the characterization of the genetically modified mice may address more general questions about how biological asymmetry is determined. Therefore, this program will have a strong impact in multiple biological science fields. Furthermore, since the proposed study will employ state-of-the-art experimental approaches in molecular and cellular biology, biochemistry, genetic engineering and electrophysiology, this program will also provide an innovative multidisciplinary training environment for graduate and undergraduate students in Canada.