前突觸Integrin訊息傳遞在突觸結構可塑性中的角色分析

Abstract

Integrin訊息傳遞參與在多種細胞的行為中，包含細胞移動、細胞附著、細胞存活及細胞生長；在神經細胞發育過程中，integrin在神經細胞表面突起之生長、軸突生長之引導、突觸之行成或是突觸可塑性中都扮演著重要的角色，以突觸的發育與維持來說，之前的研究顯示，integrin主要作用在後突觸中來對突觸進行調節；在本論文中，我們發現integrin在前突觸中對突觸結構可塑性上扮演著重要的調節角色 ；藉由Fak56基因突變株的選殖與分析，我們發現在果蠅的Fak56基因突變株中 ，其神經肌肉結點會不正常增生，且此表現形是由於前途觸失去了FAK訊息所致，在進一步的遺傳分析中顯示，integrin αPS3βν及Src激酶對前途觸中 的FAK訊息是很重要的，除此之外，在Fak56突變株中神經肌肉結點會不正常增生，是由於其前途觸中Erk激酶活性的不正常上升所致，而Erk激酶訊息下游的Fas2細胞黏蛋白也隨之下降，在Fak56突變株的遺傳修飾者的篩選中，我們進一步篩選到兩個包含RasGAP domain的基因，其為vap及NF1，其中我們發現只有NF1會與FAK56形成複合體，但有趣的是，NF1下游的cAMP訊息路徑對其扮演Fak56下游是重要的，而非其下游的Ras訊息路徑，次外我們還發現，intergin訊息傳遞的活性是受到經驗所誘發的突觸增益所調節的，再者，我們更進一步發現，黏蛋白LanA對於活化前途觸的intergin訊息是很重要的，後突觸表現及分泌的LanA才會被送到位於非活化區的突觸間隙，進而活化前途觸的intergin訊息抑制突 觸生長，然而，很多種的神經細胞活性都可調節此一黏蛋白LanA在突觸間隙的量以進一步控制突觸之生長，由此以上數據，我們認為來自後突觸的逆行訊息LanA會被送到突觸間隙中以誘發前途觸的intergin訊息活性進而使突觸生長受到抑制，此一調節會受到神經活性所控制。此份研究主要讓我們 對於前途觸的intergin訊息有全新的了解，且此一研究不論是對於經驗誘導之神經可塑性或是神經纖維瘤病人中學習記憶障礙其背後分子機轉，都使我們有更進一步的認識。

Integrin signaling involves in several different cellular processes, including migration, adhesion, survival and proliferation. In neurons, integrin participates in neurite outgrowth, axonal guidance, synaptic formation and synaptic plasticity. During hippocampus neuron synaptic development and maintenance, postsynaptic expressed integrin functions a critical role to set the synaptic property. In this dissertation, I identify the function and regulation mechanism of presynaptic integrin singaling in synaptic structural plasticity. Through the isolation of Drosophila fak, Fak56, mutants, I find FAK signaling is specifically required in presynaptic cell to confine synaptic growth at Drosophila neuromuscular junctions (NMJs). In genetic analyses, integrin αPS3βν and Src kinases are suggested to participate in this presynaptic FAK signaling. To dissect the mechanism, Erk activity is upregulated at NMJs of Fak56 mutants. Consistently, Fas2, Erk downstream target gene, is also affected in Fak56 mutants. Following that, both RasGAP domain containing genes, vap and NF1, are identified in Fak56 genetic modifier screening. Fak56 forms complex with NF1, but not Vap. Surprisingly, NF1 downstream cAMP pathway, but not Ras signaling, is required for its function in synaptic structural plasticity under Fak56 regulation. Under experience-induced synaptic potentiation condition, I find this intergin/Fak56/NF1 signaling activity modulates the structural plasticity. Furthermore, LanA, Laminin α subunit, localizes at synaptic clefts of peri-active zone and triggers presynaptic integrin signaling activation at NMJs. Only postsynaptic expressed LanA can localize at synaptic clefts and modulate presynaptic integrin signaling. Interestingly, LanA levels at synaptic clefts depend on neuronal activity. These data suggests that retrograde LanA triggers presynaptic integrin signaling in confining synaptic structural plasticity. As all above, my studies provide a new insight of integrin signaling in synaptic structural plasticity that may contribute to both experience-induced neuronal dynamic and molecular regulation mechanism of NF1 synaptic defects and learning disability.