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，形态学上至少有 45 个 不同的亚型可以通过其内部树突乔木的大小、形状和分层来区分 内丛状层（IPL）。大多数 AC 没有轴突，而是通过其整合信号传导 树枝状乔木。这种独特的排列意味着空调的形式和功能密切相关， 也许比任何其他神经元类型更重要。然而，我们对个人空调如何运作几乎一无所知。 亚型是在开发过程中指定的，或者它们如何采用其定型形态。我们假设 选择性表达的转录因子 (TF) 能够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 Isl1 仅在星爆无长突细胞 (SAC) 中表达，Gbx2 仅在先前未鉴定的细胞中表达 中场非 GABAeric、非甘氨酸能 ACs (MF-nGnGs) 群体。我们的初步结果显示 从 AC 前体中早期删除 Isl1 或 Gbx2 会导致 SAC 和 MF-nGnG 亚型缺陷 规格，分别。后来在迁移后 SAC 或 MF-nGnG 中删除 Isl1 或 Gbx2 会改变它们的 树突形态和分层模式。因此，Isl1 和 Gbx2 似乎是初始所需的 其各自的 AC 亚型的规格和随后的形态成熟。我们将在以下位置对此进行测试 具体目标如下： 1) 确定 Isl1 和 Gbx2 对于 AC 子类型是否是必要且充分的 规格和成熟度。我们将使用条件功能损失和增益方法来确定 Isl1 和 Gbx2 是否对于启动和维持终末分化是必要且充分的 分别是 SAC 和 MF-nGnG。此外，我们将结合使用基因组方法（RNASeq、 ATACseq）来识别各自 AC 亚型中的 Isl1 和 Gbx2 基因调节网络。 2）定义如何 Isl1 和 Gbx2 调节 SAC 和 MF-nGnG 形态和功能连接。我们首先要确定如何 SAC 中 Isl1 和 MF-nGnG 中 Gbx2 的缺失影响其定型树突的发育 形态和分层模式。然后我们将测试候选效应基因及其通路 参与树突乔木的建立。最后，我们将确定 Isl1 和 Gbx2 的丢失如何 影响视觉回路中 SAC 和 MF-nGnG 的功能连接。这些实验一起 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 赋予 AC 独特形态特性的分化程序。我们期望这些 研究结果将揭示广泛适用于发育中的神经系统的原理。

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.