G蛋白信號路徑與PCT-1在調控突觸小泡定位的關係

Abstract

突觸（synapse）是神經細胞建立彼此聯結的特化結構。突觸活化區蛋白（active zone protein）和突觸小泡（synaptic vesicle）的這些突觸部件必需運送到應該形成突觸的區域組成一個有功能的結構讓神經進行訊息傳導。突觸部件的運送可藉由在微管（microtubule）上移動的分子馬達來達成。先前的研究指出，Gαs蛋白信號路徑中的蛋白激酶A（PKA）參與調控動力馬達（dynein）對於細胞內分子和胞器的運輸。然而PKA在突觸部件運輸和突觸形成中的作用尚不清楚。我的研究顯示，在線蟲的神經內Gαs信號調控突觸部件運送和突觸形成。活化Gαs路徑的突變體會有突觸小泡和活化區蛋白錯誤地分佈至樹突區域以及軸突突觸數目顯著的減少。我發現Gαs/GSA-1作用於DA9神經元內並且透過腺苷酸環化酶（adenylyl cyclase）和PKA來控制突觸形成。此外，我證明了PKA和PCTAIRE激酶1（PCT-1）在突觸小泡分佈和突觸形成的調控上相互拮抗，遺傳分析顯示PKA會作用在PCT-1的下游。我進一步的研究發現gsa-1(gf)的功能需要動力馬達的組件DHC-1以及其功能調節子NUD-2的參與。總結以上結果，Gαs信號調控負責逆向運輸的動力馬達去運送突觸小泡，以及該信號會被PCT-1激酶抑制以形成正確的突觸結構和神經迴路。

Synapse requires synaptic vesicles and active zone proteins to conduct neurotransmission. Molecular motor proteins are responsible for synaptic component transport to synaptic regions on microtubules. Previous studies reported that protein kinase A (PKA), the component of Gαs protein signaling pathway, is implicated in regulating dynein-dependent cargo trafficking of intracellular molecules and organelles. However, the role of PKA in synaptic component transport and synapse formation remains unclear. Here, I showed that the Gαs signaling regulates the localization of synaptic components and synapse formation in the C. elegans. Gαs pathway activation mutants had the synaptic vesicles and active zone proteins mislocalized to the dendrites, and the number of axonal synapses was significantly reduced. I found that Gαs/GSA-1 functions cell-autonomously in DA9 neurons and acts through adenylyl cyclase and PKA to control synapse formation. Furthermore, I demonstrated that PKA and cyclin-dependent kinase PCT-1/PCTK1 antagonize each other in regulating synaptic vesicle distribution and synapse formation, and PKA likely functions downstream to PCT-1. Finally, I showed that the dynein motor component DHC-1 and its functional regulator NUD-2 are both required for gsa-1(gf) mutant phenotypes. Together, these results suggested that Gαs signaling requires dynein-mediated retrograde transport to localize synaptic vesicles to the dendrites, and this signaling is controlled by PCT-1 for correct synapse assembly and neural circuits.