The Role of Zic Genes in Patterning the Binocular Projection

描述（由申请人提供）：该资助旨在了解转录因子编码如何影响视网膜并控制引导受体表达，以建立交叉和未交叉的视觉投影。我们之前的工作定义了这样一个通过小鼠视交叉的同侧投影程序：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，从而产生同侧投影。EphrinB2在视交叉中线的径向胶质细胞上表达，EphrinB2与EphrinB2的排斥相互作用产生同侧投影。Zic2和EphB1的表达与物种间和同侧投影减少的遗传模型（如白化病）的双眼视度相关。在上一期资助期内，我们确定了EphB1在Zic2突变体中表达下调，而在异位表达Zic2后表达上调；因此，Zic2控制EphB1的表达。此外，Zic2是体内和体外驱动同侧投射的必要和充分条件。我们还发现Foxd1在VT象限表达，并且是Zic2和EphB1表达所必需的，将Foxd1置于该转录程序的上游进行同侧投射。在其他研究中，我们发现非VT和晚形成VT视网膜的RGCs表达Ig-CAM NrCAM和信号素受体PlexinA1，这两个区域都会引起对侧投影。NrCAM似乎调节了rgc对信号素的抑制反应，正如在其他系统中线交叉中发现的那样。在Aim 1中，我们将继续关注Zic2，并确定Zic2调控的其他基因。转录因子Islet2与NrCAM和PlexinA1具有相同的表达模式，但其作用与NrCAM类似，仅限于VT的晚生交叉投射。因此，我们将关注晚VT视网膜，并确定Islet2是否控制NrCAM和/或PlexinA1的表达来编码来自该区域的对侧视网膜投影。我们还将确定Islet2是否与Zic2进行功能交互。在Aim 2中，我们将寻找可能指定导致交叉和非交叉投影的视网膜部分的其他基因，并研究Foxg1 （Foxd1的鼻对应物）是否位于对侧程序的上游。在目标3中，我们将应用目标1和目标2中获得的信息来了解白化视网膜是如何（错误地）指定产生同侧投影减少的。目的4将研究对RGC和视网膜规范重要的基因是否实现中线引导和/或瞄准眼特异性区域的背外侧膝状核（dLGN）。这些研究使用了基因传递（子宫内和离体电穿孔）、体外实验和电路追踪的创新方法来定义双目视觉投影形成的分子控制。公共卫生相关性：这项研究旨在了解视网膜神经节细胞如何从每只眼睛生长出来，在x形视交叉处相遇，然后向大脑两侧的目标发散。正常的双眼视觉依赖于在视交叉处交叉的视网膜轴突的正态分布，如果发生改变，视觉敏锐度和深度感知随之降低。这项工作研究了视网膜的基因，这些基因将视网膜划分为产生交叉和非交叉投影的区域，并驱动引导受体的表达，使视网膜轴突采取适当的路线。

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.