Role of Zic Genes in Patterning the Binocular Projection

描述（由申请人提供）：视交叉中视网膜神经节细胞（RGC）投射的交叉对于视觉信息的正常映射至关重要，并确保每个半球接收来自双眼的信息以建立双眼视觉。双眼视路的发育是如何决定的一直是个谜。最近在脊髓中的研究表明，不同的神经元亚群表达同源结构域转录因子的组合，并且这种编码决定了对特定靶点的投射。我们假设，一个类似的代码的调控基因表达可能指定的非交叉和交叉的RGCs亚群。我们的实验室已经发现含有锌指的转录因子Zic 2在RGCs中以不交叉的轨迹表达。Zic 2，而不是其他Zic家族成员，是有丝分裂后，但动态地表达在RGC在腹颞（VT）视网膜的时期，当未交叉的RGC亚群项目轴突从这个位置向交叉。体外功能获得和丧失实验表明，当与交叉细胞共培养时，Zic 2是必要的并且足以将视网膜轴突的生长行为从交叉模式切换到非交叉模式，反之亦然。此外，Zic 2表达与几个物种的双眼视觉程度相关。我们实验室的其他工作已经确定EphB 1是在小鼠交叉中线与抑制因子ephrinB 2相互作用的受体系统。EphB 1在空间和时间上与Zic 2一致表达。 拟议的工作将进一步分析Zic 2通过调节Eph家族中介导视交叉中线处视网膜轴突发散的指导受体的表达来指定未交叉的视网膜神经节细胞轴突轨迹的假设。目的包括验证Zic 2在神经节细胞中以非交叉轨迹表达并阐明其时间表达（Aim 1）;通过使用体内功能丧失和获得策略，确认Zic 2对于建立非交叉轨迹是必要且充分的（Aim 2）;研究Zic 2对推定靶基因的影响，特别是关于视网膜中的EphB 1受体（Aim 3）。这一分析应阐明模式的双眼通路，并应适用于建立双边的感觉通路在神经系统的其他地方。

DESCRIPTION (provided by applicant): The decussation of the retinal ganglion cell (RGC) projections in the optic chiasm is essential for normal mapping of visual information, and insures that each hemisphere receives information from both eyes to establish binocular vision. How the development of the binocular pathway is determined has been a longstanding enigma. Recent work in the spinal cord has shown that distinct subpopulations of neurons express combinations of homeodomain transcription factors and that such code determines projection to specific targets. We hypothesized that a similar code of regulatory gene expression might designate the uncrossed and crossed subpopulations of RGCs. Our laboratory has discovered that a zinc-finger containing transcription factor Zic2, is expressed in RGCs with an uncrossed trajectory. Zic2, but not other Zic family members, is postmitotically but dynamically expressed in RGCs in ventrotemporal (VT) retina in the period when the uncrossed RGC subpopulation projects axons from this location toward the chiasm. Gain- and loss-of-function experiments in vitro indicate that Zic2 is necessary and sufficient to switch the outgrowth behavior of retinal axons when co-cultured with chiasm cells, from crossed to uncrossed patterns, or vice versa. Moreover, Zic2 expression correlates with the degree of binocular vision across several species. Other work in our lab has identified EphB1 as a receptor system interacting with the inhibitory factor ephrinB2 at the chiasm midline in mouse. EphB1 is expressed coincident with Zic2, spatially and temporally. The proposed work will further analyze the hypothesis that Zic2 specifies the uncrossed retinal ganglion cell axon trajectory, by regulating expression of guidance receptors in the Eph family that mediate retinal axon divergence at the optic chiasm midline. Aims include verification that Zic2 is expressed in ganglion cells with an uncrossed trajectory and elucidation of its temporal expression (Aim1); confirmation that Zic2 is necessary and sufficient to establish an uncrossed trajectory, by using loss- and gain-of-function strategies in vivo (Aim 2); investigation of Zic2's influence on genes that are putative targets, especially with regard to the EphB1 receptor in the retina (Aim 3). This analysis should shed light on patterning the binocular pathway and should apply to the establishment of bilateral sensory pathways elsewhere in the nervous system.