The role of BARHL2 in the mosaic pattering and dendritic tiling of retinal amacri

描述（由申请人提供）：我们准确的视觉取决于视觉信息通过不同视网膜神经元的轴突和树突之间的精确有线连接的流动。在视网膜中，神经元占据空间域并使它们的树突树枝化，这需要它们的细胞体和树突树枝的适当分布。同一类型的神经元的细胞体在一个称为马赛克图案的过程中被隔开，它们的树突建立一个区域，在该区域内，同一类型的其他细胞被排除在外，这个过程称为平铺。此外，来自单个细胞的神经突显示出自我回避的特性。相比 尽管在发现视网膜细胞命运决定和分化的基因和机制方面取得了巨大进展，但对视网膜以及其他神经系统中镶嵌图案形成和平铺过程的分子机制知之甚少。直到最近，研究表明，在唐氏综合征细胞粘附分子（DSCAM）、DSCAM样1（DSCAML 1）、MEG 10和PCDH突变小鼠中，某些类型的视网膜无长突细胞和神经节细胞表现出细胞体间距和树突状分支的缺陷，这开始暗示独特类别的细胞粘附分子（CAM）在脊椎动物视网膜中调节这些过程中的作用。然而，我们还没有发现在近80种视网膜细胞类型和亚型中参与这些过程的其他分子，更重要的是，要确定和表征控制功能神经回路形成的整个基因和遗传途径。在过去，由于缺乏合适的分子，这个问题一直难以解决。在这里，我们表明，在缺乏BARHL 2，一个BAR同源结构域转录因子的小鼠，在神经节细胞层的星爆无长突细胞有聚集的树突和丛生的细胞体，表明Barhl 2的自我回避的作用。作为第一个涉及神经元镶嵌图案和平铺过程的转录因子，BARHL 2提供了一个独特的机会，最终确定神经元镶嵌图案和平铺形成的遗传途径。在这个建议中，我们将充分表征的马赛克图案和平铺表型的星爆无长突细胞的神经节细胞层的Barhl 2无效的视网膜。第二，为了恢复自我回避的遗传途径，我们将进行Barhl 2野生型和无效星爆无长突细胞的RNA-Seq和BARHL 2 ChIP-Seq，以筛选Barhl 2的下游靶基因，并鉴定调节星爆无长突细胞的平铺和镶嵌图案化过程的转录网络。总之，这些研究将定义Barhl 2在调节星爆无长突细胞的平铺和镶嵌图案化过程中的作用，并阐明Barhl 2下游发生的转录事件。

DESCRIPTION (provided by applicant): Our accurate vision depends on the flow of visual information through precisely wired connections between axons and dendrites of different retinal neurons. In the retina, neurons occupy spatial domains and arborize their dendrites, which require the proper distribution of their cell bodies and dendritic arbors. Cell bodies of the same type of neurons are spaced out in a process called mosaic patterning, and their dendrites establish a zone within which other cells of the same type are excluded, a process called tiling. In addition, the neurites from an individual cell display self-avoidance properties. In contrast to the excellent progress made in discovering genes and mechanisms of retinal cell fate determination and differentiation, relatively little is known about the molecular mechanisms underlying the mosaic patterning and tiling processes in the retina as well as in other nervous systems. Not until recently, studies show that in mice mutant for Down syndrome cell adhesion molecule (DSCAM), DSCAM-LIKE1 (DSCAML1), MEG10, and PCDH, certain types of retinal amacrine and ganglion cells exhibit defects in the spacing of cell bodies and in the dendritic arborization, which begins to implicate the roles of unique classes of cell adhesion molecules (CAMs) in regulating these processes in the vertebrate retina. Nevertheless, we have yet to uncover the other molecules involved in these processes in each of the nearly 80 retinal cell types and subtypes, and more importantly, to identify and characterize the entire genes and genetic pathways that govern the formation of functional neural circuitry. In the past, this question has been hard to address due to the lack of a suitable molecule. Here, we show that in mice lacking BARHL2, a BAR-homeodomain transcription factor, starburst amacrine cells in the ganglion cell layer have aggregated dendrites and clumped cell bodies, indicating Barhl2's role in self-avoidance. Being the first transcription factor implicated in neuronal mosaic patterning and tiling processes, BARHL2 offers a unique opportunity to ultimately identify genetic pathways of neuronal mosaic patterning and tiling formation. In this proposal, we will fully characterize th mosaic patterning and tiling phenotypes of starburst amacrine cells in the ganglion cell layer of the Barhl2-null retina. Second, to recover the genetic pathway of self-avoidance, we will perform RNA-Seq of Barhl2 wild type and null starburst amacrine cells and BARHL2 ChIP-Seq to screen for downstream target genes of Barhl2 and to identify the transcriptional network regulating the tiling and mosaic patterning processes of starburst amacrine cells. Together, these studies will define the role of Barhl2 in regulating the tiling and mosaic patterning processes of starburst amacrine cells and elucidate the transcriptional events that occur downstream of Barhl2.