MOLECULAR MECHANISMS OF RETINAL CIRCUIT ASSEMBLY

轴突和树突的形态塑造了神经元回路的连通性和功能; 畸形轴突和树突是神经发育障碍的共同特征。为了建立细胞类型特异性的形态，发育中的神经突需要（1）朝向正确的位置生长并形成分支（即神经突 （2）具有不同分支模式和几何形状（即神经突形状）的精心制作的乔木，以及（3） 占据适当的区域（即神经突大小）。轴突和树突如何生长到一个确切的大小， 调节连接性，以及它如何影响特定的电路计算还没有很好地理解。初步 在研究中，我们鉴定了四种细胞粘附分子（CAM; Amigo 1，Amigo 2，netrin-G1和NGL 1）， 视网膜的两个回路中神经元的树突和轴突大小：方向选择（DS）回路，其提取 运动信息的内部视网膜，和杆双极通路，其传输昏暗的光信号从 外层到内层视网膜。星爆细胞具有径向对称的乔木，相邻细胞之间广泛重叠 Amigo 2快递每个心轴的中心三分之二接收输入，外围三分之一提供输出。 来自星状细胞的抑制性输入对于神经节细胞的DS反应是至关重要的。星爆细胞的神经突大小是 在Amigo 2敲除（Amigo 2-/-）小鼠中增加，同时维持功能区室化。在目标1中， 我们将分析Amigo 2作用的分子机制，测试其对神经突形态的影响， 连接性、DS电路功能以及图像稳定头部和眼睛运动。在杆的第一阶段 在双极通路中，水平细胞轴突介导视杆之间的侧抑制，其向视杆双极提供输入。 树突水平细胞表达Amigo 1。在Amigo 1-/-小鼠中，水平细胞轴突和杆双极树突被 都缩小了尺寸。在目标2中，我们将描述Amigo 1的信号传导机制，探索 突触伴侣之间的匹配，分析对连接的影响，并测量沿着杆的光敏感性 双极通路和行为反应。在视杆双极通路的第二阶段，表达netrin-G1的视杆双极轴突与表达NGL 1的AII细胞突触。在netrin中，杆双极轴突尺寸减小- G1-/-和NGL 1-/-小鼠，表明跨突触netrin-G1/NGL 1复合物的逆行信号调节 轴突生长在目标3中，我们将探讨前向信号是否控制AII刀轴尺寸。我们将决定如何 netrin-G1/NGL 1复合物影响视杆细胞双极间突触的数量、超微结构和功能， AII细胞，并评估它们对沿着杆双极通路的光反应和对小鼠能力的影响。 来探测微弱的闪光这些研究将共同提供对分子机制的见解， 视网膜中轴突和树突的大小，揭示了轴突大小如何调节连接，以及它如何形成特定的形状。 电路计算和影响视觉引导的行为。

The morphology of axons and dendrites shapes the connectivity and function of neuronal circuits; and dysmorphic axons and dendrites are a common feature of neurodevelopmental disorders. To establish cell-type-specific morphologies, developing neurites need to (1) grow towards and branch in the right places (i.e. neurite targeting), (2) elaborate arbors with distinct branching patterns and geometries (i.e. neurite shape), and (3) occupy appropriate territories (i.e. neurite size). How axons and dendrites grow to an exact size, how arbor size regulates connectivity, and how it influences specific circuit computations is not well understood. In preliminary studies, we identified four cell adhesion molecules (CAMs; Amigo1, Amigo2, netrin-G1, and NGL1) that regulate dendrite and axon size of neurons in two circuits of the retina: the direction selective (DS) circuit, which extracts motion information in the inner retina, and the rod bipolar pathway, which transmits dim-light-signals from the outer to the inner retina. Starburst cells have radially symmetric arbors that overlap extensively among neighbors and express Amigo2. The central two thirds of each arbor receive input and the peripheral third provides output. Inhibitory input from starburst cells is critical for DS responses of ganglion cells. Neurite size of starburst cells is increased in Amigo2 knockout (Amigo2-/-) mice, while functional compartmentalization is maintained. In Aim 1, we will analyze the molecular mechanisms of Amigo2’s actions, test its influence on neurite morphology and connectivity, DS circuit function, and image stabilizing head and eye movements. At the first stage of the rod bipolar pathway, horizontal cell axons mediate lateral inhibition among rods, which provide input to rod bipolar dendrites. Horizontal cells express Amigo1. In Amigo1-/- mice, horizontal cell axons and rod bipolar dendrites are both reduced in size. In Aim 2, we will characterize the signaling mechanism of Amigo1, explore territory matching between synaptic partners, analyze effects on connectivity and measure light sensitivity along the rod bipolar pathway, and in behavioral responses. At the second stage of the rod bipolar pathway, netrin-G1-expressing rod bipolar axons synapse onto NGL1-expressing AII cells. Rod bipolar axon size is reduced in netrin- G1-/- and NGL1-/- mice, suggesting that retrograde signals of trans-synaptic netrin-G1/NGL1 complexes regulates axon growth. In Aim 3, we will explore whether forward signals control AII arbor size. We will determine how netrin-G1/NGL1 complexes affect the number, ultrastructure and function of synapses between rod bipolar and AII cells, and assess their influences on light responses along the rod bipolar pathway and on the ability of mice to detect dim light flashes. Together these studies will provide insights into the molecular mechanisms that control axon and dendrite size in the retina, reveal how neurite size regulates connectivity, and how it shapes specific circuit computations and influences visually guided behaviors.