Investigating the Role of Nephronectin in Establishing Retinotectal Circuit Specificity

项目摘要 神经系统的一个令人印象深刻的特征是它的突触连接的专一性。在大脑中，一个 单个神经元能够正确地识别并突触到其适当的信号伙伴上，而不是数十亿个其他神经元 神经元。如何达到这种程度的专一性是深入研究的主题。虽然取得了巨大的进步，但 在识别参与远程轴突引导和地形定位的分子方面取得了进展， 当轴突到达预定的目标区域时，是什么分子引导它们进入合适的板层，目前还知之甚少。 通过筛选广域神经元差异表达的细胞外基质蛋白 上丘(SC)的视网膜浅灰质层(SGS)，我鉴定为肾连结蛋白(Npnt)。 作为视网膜顶盖回路中调节突触特异性的候选者。NPNT属于EGF样超家族 细胞外基质糖蛋白，并已被很好的生化特征，强烈结合和 具体为整合素α8β1(ITGα8β1)。 我的初步数据显示：1)Npnt仅由SC的广域神经元表达，其细胞 下部SGS内有一层；2)Npnt沉积在宽体细胞和近端的树突上。 野神经元，3)孤束核中Npnt的丢失导致上孤束核内异位的αRGC轴突，以及4)α 视网膜神经节细胞(αRGC)表达ITGα8β1 在开发过程中， 与ITGα8β1作为 α视网膜节细胞上的NPNT受体。综上所述，我假设NPNT指示αRGC轴突在 α-8-β-1通过与α视网膜节细胞结合，使α视网膜节细胞具有突触特异性。 野战神经元。这项提案将解决RGC如何与它们的神经元伙伴形成精确的连接 通过研究Npnt如何调节轴突板层靶向和突触的形成。在目标1中，我将确定 Npnt如何通过关注其与αα8β1的相互作用来介导轴突板层靶向RGC。在目标2中，我将 确定NPNT如何影响SC内αRGC突触伙伴的选择。完成拟议的 实验将揭示独特的分子和细胞机制关于Npnt在 从α视网膜节细胞到广域神经元的神经元配对，将有助于阐明NpnT在哺乳动物中的功能 神经系统。

PROJECT ABSTRACT An impressive feature of the nervous system is the specificity of its synaptic connections. Within the brain, a single neuron is able to correctly identify and synapse onto its proper signaling partner over billions of other neurons. How this degree of specificity is achieved is the subject of intense research. While great progress has been made in identifying molecules that participate in long-range axon guidance and topographic positioning, little is known in what molecules guide axons into their proper lamina once they reach their destined target region. Through screening for extracellular matrix proteins differentially expressed by wide-field neurons in the retinorecipient stratum griseum superficiale (SGS) of the superior colliculus (SC), I identified nephronectin (Npnt) as a candidate for mediating synaptic specificity in retinotectal circuits. Npnt belongs to the EGF-like superfamily of extracellular matrix glycoproteins and has been biochemically well-characterized to bind strongly and specifically to integrin α8β1 (Itgα8β1). My preliminary data show that 1) Npnt is exclusively expressed by wide-field neurons of the SC, whose cell bodies define a lamina within the lower SGS; 2) Npnt deposits on the somata and proximal dendrites of wide- field neurons, 3) loss of Npnt in the SGS results in ectopic αRGC axons within the upper SGS, and 4) alpha retinal ganglion cells (αRGCs) express Itgα8β1 during development, consistent with Itgα8β1 acting as the receptor for Npnt on αRGCs. Taken altogether, I hypothesize that Npnt instructs αRGC axons to laminate within the lower SGS through binding Itgα8β1 on αRGCs, thereby conferring synaptic specificity of αRGCs onto wide- field neurons. This proposal will address how RGCs form precise connections to their neuronal partners within the SC by studying how Npnt regulates axon laminar targeting and synapse formation. In Aim 1, I will determine how Npnt mediates axon laminar targeting of αRGCs by focusing on its interactions with Itgα8β1. In Aim 2, I will determine how Npnt affects αRGC synaptic partner choice within the SC. Completion of the proposed experiments will reveal unique molecular and cellular mechanisms regarding the role of Npnt in specifying neuronal pairing from αRGCs to wide-field neurons and will shed light on the function of Npnt in the mammalian nervous system.