The Role of Zic Genes in Patterning the Binocular Projection

描述(申请人提供)：这项资助申请旨在了解视网膜模式的基因通路，并控制引导受体的表达，以建立交叉和非交叉的视觉投影。我们以前的工作为未交叉或同侧的投射定义了这样的程序：引导受体EphB1在腹颞(VT)视网膜神经节细胞(RGCs)中表达，表达EphB1的VT RGCs和表达EPhinB2的视交叉中线的放射状胶质细胞之间的排斥作用建立了同侧投射。转录因子Zic2控制EphB1的表达，是诱导同侧投射的必要条件和充分条件，并调节对活性依赖的靶神经支配至关重要的因子。我们最近发现了对侧RGC的中线引导程序：对侧RGC和视交叉细胞表达的Ig-CAM Nr-CAM和信号素受体Plexin-A1与中线Sema6D形成复合体，将抑制转化为对侧RGC轴突的生长。然而，对侧RGC投射的转录控制知之甚少。拟议的研究试图揭示控制同侧和对侧RGC身份和视网膜模式的转录网络。目标1将分析对侧投射的转录途径。我们发现，SoxC转录因子(Sox4、11和12)在交叉的RGC中表达，并与Plexin-A1和Nr-CAM的启动子区域结合。使用有条件地移除所有三个SOXCs的小鼠模型，我们将确定SOXCs是否通过指导对侧导向分子的表达来调节对侧投射。我们还将确定Zic2是否抑制对侧基因以保持未交叉的RGC身份。在目标2中，我们将通过关注目标1中所研究的转录因子的上游，即FOXG1和Foxd1，进一步研究交叉和非交叉投影是如何被指定的。Foxd1在VT视网膜中表达，是Zic2和EphB1表达所必需的，因此将其置于同侧投射的转录程序的上游。正如FOXG1在 为了研究引起对侧投射视网膜节细胞的区域，我们将使用一只新的条件FOXG1小鼠，研究FOXG1是否通过调节对侧基因表达来控制对侧投射。在目标3中，我们以我们最近在基因表达谱方面的成功为基础，识别在同侧和对侧视网膜节细胞中差异表达的基因。我们将描述它们的表达模式和在指导双目环路形成中的作用。总而言之，这些研究将阐明同侧和对侧视网膜部分是如何被指定的--这些信息对于实现本土RGC或其干细胞替代的再生至关重要。

DESCRIPTION (provided by applicant): This grant application aims to understand the gene pathways that pattern the retina and control guidance receptor expression to establish the crossed and uncrossed visual projections. Our previous work defined such a program for the uncrossed or ipsilateral projection: the guidance receptor EphB1 is expressed in ventrotemporal (VT) retinal ganglion cells (RGCs), and repulsive interactions between EphB1-expressing VT RGCs and EphrinB2-expressing radial glia at the optic chiasm midline establish the ipsilateral projection. The transcription factor Zic2 controls EphB1 expression, is necessary and sufficient for inducing an ipsilateral projection, and regulates factors important for activity-dependent target innervation. We have recently identified a contralateral RGC midline guidance program: the Ig-CAM Nr-CAM and the semaphorin receptor Plexin-A1, expressed by contralateral RGCs and optic chiasm cells, form a complex with midline Sema6D to convert inhibition into growth of contralateral RGC axons. However, little is known about the transcriptional control of the contralateral RGC projection. The proposed studies seek to uncover transcriptional networks controlling ipsilateral and contralateral RGC identity and retinal patterning. Aim 1 will analyze transcriptional pathways of the contralateral projection. We have discovered that the SoxC group of transcription factors (Sox4, 11 and 12) is expressed in crossed but not uncrossed RGCs and binds to the promoter regions of Plexin-A1 and Nr-CAM. Using a mouse model conditionally removing all three SoxCs, we will determine whether SoxCs regulate the contralateral projection through directing contralateral guidance molecule expression. We will also determine whether Zic2 represses contralateral genes to maintain uncrossed RGC identity. In Aim 2, we will further investigate how crossed and uncrossed projections are specified by focusing on transcription factors upstream of those studied in Aim 1, namely, Foxg1 and Foxd1. Foxd1 is expressed in the VT retina and is required for Zic2 and EphB1 expression, thus placing it upstream of the transcriptional program for the ipsilateral projection. As Foxg1 is expressed in the areas giving rise to contralaterally projecting RGCs, we will investigate whether Foxg1 controls the contralateral projection through regulation of contralateral gene expression, using a novel conditional Foxg1 mouse. In Aim 3, we build on our recent success in gene expression profiling to identify genes that are differentially expressed in ipsilateral versus contralateral RGCs. We will characterize their expression patterns and roles in directing the formation of the binocular circuit. Together, these studies will illuminate how the ipsilateral and contralateral retinal sectors are specified - information that is essential for implementing regeneration of indigenous RGCs or their stem cell replacements.