The Role of Zic Genes in Patterning the Binocular Projection

描述(申请人提供)：这项资助旨在了解转录因子编码如何形成视网膜的模式，并控制引导受体的表达，以建立交叉和非交叉的视觉投影。我们以前的工作为小鼠视交叉的同侧投射定义了这样一个程序：转录因子Zic2和引导受体EphB1在腹颞(VT)视网膜神经节细胞(RGCs)中表达，从而产生同侧投射。EPhinB2表达于视交叉中线的放射状胶质细胞，EphB1与EphinB2的相互排斥作用产生同侧投射。ZIC2和EphB1的表达与物种间的双目程度相关，在同侧投影减少的遗传模型中，如白化病。在上一个资助阶段，我们确定了EphB1在Zic2突变体中表达下调，在Zic2异位表达后上调，因此Zic2控制EphB1的表达。此外，Zic2是在体内和体外驱动同侧投射的必要条件和充分条件。我们还发现，Foxd1在VT象限表达，是Zic2和EphB1表达所必需的，将Foxd1置于同侧投射的转录程序的上游。在其他研究中，我们发现Ig-CAM NrCAM和Semaphorin受体PlexinA1在非VT和晚期VT视网膜的RGC中表达，这两个区域都产生了对侧投射。NrCAM似乎调制了视网膜节细胞对信号素的抑制反应，就像在其他系统的中线交叉中发现的那样。在目标1中，我们将继续关注Zic2，并确定更多受Zic2调控的基因。转录因子Islet2与NrCAM和PlexinA1具有相同的表达模式，但其作用仅限于VT的晚期交叉投影，与NrCAM相似。因此，我们将关注VT晚期的视网膜，并确定Islet2是否控制NrCAM和/或PlexinA1的表达，以编码来自该区域的对侧视网膜投射。我们还将确定Islet2是否在功能上与Zic2交互。在目标2中，我们将寻找其他基因，这些基因可能指定导致交叉和非交叉投影的视网膜部分，并调查FOXG1(Foxd1的鼻部对应物)是否位于对侧程序的上游。在目标3中，我们将应用从目标1和2获得的信息来理解白化视网膜是如何被指定(Mis)以产生减少的同侧投影的。目的4将检查对RGC和视网膜规范重要的基因是否实施中线引导和/或定位背侧膝状核(DLGN)中的眼睛特异区。这些研究使用创新的基因传递方法(子宫内和体外电穿孔)、体外分析和电路追踪来确定双眼视觉投射形成的分子控制。与公共健康相关：这项研究旨在了解视网膜神经节细胞是如何从每只眼睛长出来的，在X形视交叉相遇，然后向大脑两侧的目标发散。正常的双眼视觉取决于视交叉处视网膜轴突的正常分布，如果改变，视力和深度知觉就会降低。这项工作研究了将视网膜分成几个扇区的基因，这些扇区产生交叉和非交叉投射，并驱动引导受体的表达，使视网膜轴突走上适当的路线。

DESCRIPTION (provided by applicant): This grant is aimed at understanding how transcription factor codes 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 ipsilateral projection through the mouse optic chiasm: The transcription factor Zic2 and the guidance receptor EphB1 are expressed in ventrotemporal (VT) retinal ganglion cells (RGCs), which give rise to the ipsilateral projection. EphrinB2 is expressed on radial glia at the optic chiasm midline, and the repulsive EphB1-ephrinB2 interaction produces the ipsilateral projection. Zic2 and EphB1 expression correlate with the degree of binocularity across species and in genetic models with a reduced ipsilateral projection, such as the albino. In the last funding period, we determined that EphB1 expression is downregulated in Zic2 mutants and upregulated after ectopic expression of Zic2; thus, Zic2 controls EphB1 expression. Further, Zic2 is necessary and sufficient to drive an ipsilateral projection in vivo and in vitro. We also found that Foxd1 is expressed in the VT quadrant and is required for Zic2 and EphB1 expression, placing Foxd1 upstream of this transcriptional program for the ipsilateral projection. In other studies, we found that the Ig-CAM NrCAM and the Semaphorin receptor PlexinA1 are expressed by RGCs in non-VT and late-forming VT retina, both regions giving rise to the contralateral projection. NrCAM appears to modulate an inhibitory response by RGCs to semaphorins, as found for midline crossing in other systems. In Aim 1, we will continue a focus on Zic2 and identify additional genes regulated by Zic2. The transcription factor Islet2 has an identical expression pattern to NrCAM and PlexinA1, but its role is restricted to the late-born crossed projection from VT, similar to NrCAM. Therefore, we will focus on the late VT retina and determine whether Islet2 controls NrCAM and/or PlexinA1 expression to encode the contralateral retinal projection from this region. We will also determine if Islet2 interacts functionally with Zic2. In Aim 2, we will search for additional genes that may specify the retinal sectors giving rise to the crossed and uncrossed projection, and investigate whether Foxg1 (the nasal counterpart to Foxd1) is upstream of the contralateral program. In Aim 3, we will apply information gained from Aims 1 and 2 to understand how the the albino retina is (mis)specified to produce a diminished ipsilateral projection. Aim 4 will examine whether the genes important for RGC and retinal specification implement midline guidance and/or targeting of eye- specific zones in the dorsal lateral geniculate nucleus (dLGN). These studies use innovative methods for gene delivery (in utero and ex vivo electroporation), in vitro assays, and circuit tracing to define the molecular control of the formation of binocular visual projections. PUBLIC HEALTH RELEVANCE: This research aims to understand how retinal ganglion cells grow out from each eye, meet at the X-shaped optic chiasm, then diverge toward targets on both sides of the brain. Proper binocular vision is dependent on a normal distribution of retinal axons crossing at the optic chiasm, and if altered, reduced visual acuity and depth perception ensue. This work investigates the genes that pattern the retina into sectors giving rise to crossed and uncrossed projections and that drive expression of guidance receptors to enable retinal axons to take the appropriate route.