Supplement to: Transcription control of retinal neuron specification and maturation

项目概要/摘要 无长突细胞（AC）是视网膜内层的主要抑制性神经元，在形态上至少有45个 不同的亚型，可以通过其树突状乔木的大小，形状和分层来区分， 内丛状层（IPL）。大多数AC没有轴突，而是将信号整合到它们的轴突上。 树枝状乔木这种独特的排列意味着AC的形式和功能密切相关， 也许比其他任何类型的神经元都要多。然而，我们几乎不知道个体AC 亚型在发育过程中被指定，或者它们如何采用它们的定型形态。我们假设 选择性表达的转录因子（TF）可以很好地指导亚型特异性遗传程序， 指定并指导AC的形态成熟。在AC群体中，同源域TF Isl 1仅在星爆状无长突细胞（SACs）中表达，Gbx 2仅在先前未鉴定的 中场非GABA能、非甘氨酸能AC（MF-nGnG）群体。我们的初步结果表明 AC前体中Isl 1或Gbx 2的早期缺失导致SAC和MF-nGnG亚型的缺陷 规格，分别。迁移后SAC或MF-nGnGs中Isl 1或Gbx 2的后期缺失改变了它们的表达。 树枝状形态和分层模式。因此，Isl 1和Gbx 2似乎是初始 它们各自的AC亚型的特化和随后的形态成熟。我们将在 具体目的如下：1）确定Isl 1和Gbx 2是否是AC亚型所必需和充分的 规范和成熟。我们将使用功能的条件损失和获得方法来确定 Isl 1和Gbx 2是否都是启动和维持终末分化所必需的， SAC和MF-nGnG。此外，我们将使用基因组方法的组合（RNASeq， ATACseq）来鉴定相应AC亚型中的Isl 1和Gbx 2基因调节网络。2)定义如何 Isl 1和Gbx 2调节SAC和MF-nGnG的形态和功能连接。我们先来看看 SAC中Isl 1和MF-nGnGs中Gbx 2的缺失影响其定型树突状细胞的发育， 形态和分层模式。然后，我们将测试候选效应基因和途径， 参与树枝状乔木的建立。最后，我们将确定Isl 1和Gbx 2的丢失如何 影响视觉回路中SAC和MF-nGnG的功能连接。总之，这些实验是 有望揭示选择性表达的转录因子如何指定AC亚型和驱动终端 这些分化程序赋予AC独特的形态学特性。我们预计这些 研究结果将揭示广泛适用于发育中的神经系统的原则。

PROJECT SUMMARY/ABSTRACT Amacrine cells (ACs) are the principle inhibitory neurons of the inner retina, with at least 45 morphologically distinct subtypes that can be distinguished by the size, shape, and stratification of their dendritic arbors within the inner plexiform layer (IPL). Most ACs do not have axons, and instead integrate signaling across their dendritic arbors. This unique arrangement means that form and function are intimately related in ACs, perhaps more so than in any other neuron type. However, we know virtually nothing about how individual AC subtypes are specified during development, or how their adopt their stereotyped morphologies. We hypothesize that selectively expressed transcription factors (TFs) are well poised to direct subtype-specific genetic programs that specify and direct the morphological maturation of ACs. Within the AC population, the homeodomain TF Isl1 is only expressed in starburst amacrine cells (SACs) and Gbx2 is only expressed in a previously unidentified population of medium-field non-GABAeric, non-Glycinergic ACs (MF-nGnGs). Our preliminary results show that early deletion of Isl1 or Gbx2 from AC precursors results in defects in SAC and MF-nGnG subtype specification, respectively. Later deletion of Isl1 or Gbx2 in post-migratory SACs or MF-nGnGs alters their dendritic morphology and stratification patterns. Therefore, Isl1 and Gbx2 appear to be required for the initial specification and the subsequent morphological maturation of their respective AC subtypes. We will test this in the following Specific Aims: 1) Determine whether Isl1 and Gbx2 are necessary and sufficient for AC subtype specification and maturation. We will use conditional loss- and gain-of function approaches to determine whether Isl1 and Gbx2 are both necessary and sufficient to initiate and maintain terminal differentiation in SACs and MF-nGnGs, respectively. Furthermore, we will use a combination of genomic approaches (RNASeq, ATACseq) to identify the Isl1 and Gbx2 gene regulator networks in the respective AC subtypes. 2) Define how Isl1 and Gbx2 regulate SAC and MF-nGnG morphology and functional connectivity. We will first identify how the loss of Isl1 in SACs and Gbx2 in MF-nGnGs affects the development of their stereotyped dendritic morphology and stratification patterns. Then we will test candidate effector genes and pathways for their involvement in the establishment of dendritic arbors. Finally, we will determine how the loss of Isl1 and Gbx2 affects the functional connectivity of SACs and MF-nGnGs in visual circuits. Together, these experiments are expected to reveal how selectively expressed transcription factors specify AC subtypes and drive terminal differentiation programs that endow ACs with their unique morphological properties. We expect that these findings will reveal principles that are broadly applicable across the developing nervous system.