Molecular Mechanisms of CTIP2 Function in Corticospinal Motor Neuron Development

描述（由申请人提供）：拟议实验的长期目标是阐明对皮质脊髓运动神经元（CSMN）（和相关的新皮质投射神经元）的神经元亚型特异性发育的分子遗传控制，并可能使未来的方法能够修复退化或受损的CSMN。CSMN是所有新皮层投射神经元的发育原型，并且作为在肌萎缩侧索硬化/运动神经元疾病（ALS/MND）中退化的脑神经元和其轴突损伤是脊髓损伤中运动功能丧失的中心，具有临床重要性。本实验将深入研究中枢重要的CSMN/脑下特异性转录因子CTIP 2（COUP-TF interacting protein 2）及其副产物CTIP 1在小鼠新皮层CSMN及相关神经元发育中的作用。 Ctip 2越来越多地成为CSMN发育和连接的关键调节因子，并且作为多个投射神经元亚型分化途径的调节（主要是抑制）的共同靶标。已知Ctip 2在其他器官系统中参与发育谱系特化决定。在新皮质内，CTIP 2由CSMN和相关的脑下投射神经元特异性表达，并且对于CSMN轴突的生长、成束和靶向是必需的。虽然Ctip 2已经成为CSMN发展的核心重要因素，但其功能的大部分方面仍然未知。 大量的初步数据支持这些目标。该实验室先前的工作将Ctip 2鉴定为关键的CSMN分子控制，并证明Ctip 2-/-小鼠中的CSMN轴突在穿透内囊（IC）之前被错误路由，在IC中去束，并且未能投射到脊髓（SC）。由于CTIP 2还控制纹状体中型多刺神经元（MSN）的分化，这些神经元在IC中围绕CSMN轴突，因此假设Ctip 2-/- CSMN与SC连接的一些缺陷可能是由于Ctip 2-/- MSN中轴突生长和指导控制的失调。小鼠缺乏Ctip 2只在新皮层（Emx 1-Cre; Ctip 2fl/fl）显示，一个子集的CSMN进入和束状的IC，有些甚至达到SC。其他初步研究发现，Ctip 2 partial Ctip 1相互作用的交叉抑制与Ctip 2控制深层投射神经元的发展，Ctip 1还调节区域组织。 拟议的实验将：（目的1，2）描述Ctip 2在CSMN轴突生长和成束中的CSMN自主和非CSMN自主作用;（目的3，4）研究新鉴定的遗传交叉抑制相互作用 Ctip 2与Ctip 1在CSMN发育中的关系，以及Ctip 1在其他深层投射神经元的区域组织和发育中的独立作用。超出该提议的实验可以鉴定CSMN中由Ctip 2直接或间接调控的基因。这些研究将阐明Ctip 2（CSMN分化的中央调节因子）单独或与其他基因一起作用的机制，以指导这种发育原型的临床重要神经元类型的发育精度。 公共卫生相关性：退化性和创伤性神经系统疾病是造成巨大个人痛苦和残疾的根源，给公共卫生造成巨大的财政和社会负担;这些疾病包括涉及称为“皮质脊髓运动神经元”（CSMN）的大脑皮质“长连接”神经细胞的神经变性疾病，例如ALS /“Lou Gehrig病”，原发性侧索硬化（PLS），遗传性痉挛性截瘫（HSP），和亨廷顿病（HD）;和创伤性脊髓损伤（SCI）。Ctip 2基因和分子越来越多地成为CSMN发育和功能的关键控制因素，也是控制大脑发育和功能的中枢通路的关键调节“枢纽”，但其功能的大部分方面仍然未知。基于最近的工作，确定了对这些“大脑皮层到脊髓”脑神经元生长和功能的分子控制，该项目将对Ctip 2如何调节神经元的生长和功能进行最先进的研究。 这种重要的神经元类型在小鼠中的生长、健康和正确功能，为治疗大脑皮层中受损或退化的神经元提供新的方法，大脑皮层是大脑的最高区域，连接到脊髓，是人类ALS、SCI、HSP、PLS的中心。

DESCRIPTION (provided by applicant): The long-term goals of the proposed experiments are both to elucidate molecular-genetic controls over the neuron subtype-specific development of corticospinal motor neurons (CSMN) (and related neocortical projection neurons), and to potentially enable future approaches to repair of degenerating or injured CSMN. CSMN are both developmentally prototypical for all neocortical projection neurons, and clinically important as the brain neurons that degenerate in amyotrophic lateral sclerosis / motor neuron disease (ALS/MND) and whose axonal injury is central to loss of motor function in spinal cord injury. Proposed experiments will deeply investigate function of the centrally important CSMN/subcerebral-specific transcription factor CTIP2 (COUP-TF interacting protein 2) and its paralog CTIP1 in development of CSMN and related neurons in murine neocortex. Ctip2 has increasingly emerged as both a critical regulator of development and connectivity of CSMN, and as a common target for regulation (largely repression) by multiple projection neuron subtype differentiation pathways. Ctip2 is known from other organ systems to be involved in developmental lineage specification decisions. Within the neocortex, CTIP2 is specifically expressed by CSMN and related subcerebral projection neurons, and is necessary for outgrowth, fasciculation, and targeting of CSMN axons. While Ctip2 has emerged as centrally important for CSMN development, most aspects of its function remain unknown. Substantial preliminary data support these aims. Previous work from this laboratory identified Ctip2 as a critical CSMN molecular control, and demonstrated that CSMN axons in Ctip2-/- mice are misrouted before penetrating the internal capsule (IC), defasciculate in the IC, and fail to projec to the spinal cord (SC). Because CTIP2 also controls differentiation of striatal medium-sized spiny neurons (MSN), which surround CSMN axons in the IC, the hypothesis is suggested that some defects in Ctip2-/- CSMN connectivity to SC might result from dysregulation of axon growth and guidance controls in Ctip2-/- MSN. Mice lacking Ctip2 only in neocortex (Emx1-Cre;Ctip2fl/fl) reveal that a subset of CSMN enter and fasciculate in the IC, and some even reach the SC. Other preliminary studies find that the Ctip2 paralog Ctip1 interacts cross-repressively with Ctip2 to control deep-layer projection neuron development, and that Ctip1 additionally regulates areal organization. Proposed experiments will: (Aims 1, 2) delineate CSMN-autonomous and non-CSMN-autonomous roles of Ctip2 in CSMN axon growth and fasciculation; (Aims 3, 4) investigate a newly-identified genetically cross- repressive interaction between Ctip2 and its paralog Ctip1 in CSMN development, as well as independent roles of Ctip1 in areal organization and development of other deep-layer projection neurons. Experiments beyond this proposal could identify genes regulated directly or indirectly by Ctip2 in CSMN. These studies will elucidate mechanisms by which Ctip2, a central regulator of CSMN differentiation, acts alone and with other genes to instruct the precision of development of this developmentally prototypical, clinically important neuron type. PUBLIC HEALTH RELEVANCE: Degenerative and traumatic neurological disorders are the source of great personal suffering and disability, and they account for a huge public health financial and social burden; these include neurodegenerative diseases involving cerebral cortex "long-connection" nerve cells termed "corticospinal motor neurons" (CSMN), such as ALS / "Lou Gehrig's disease", primary lateral sclerosis (PLS), hereditary spastic paraplegia (HSP), and Huntington's disease (HD); and traumatic spinal cord injury (SCI). A gene and molecule called Ctip2 has increasingly emerged as both a critical control over development and function of CSMN, and as a key regulatory "hub" for central pathways controlling brain development and function more generally, but most aspects of its function remain unknown. Building on recent work identifying molecular controls over these "cerebral cortex-to-spinal cord" brain neurons' growth and function, this project will pursue state-of-the-art investigation of how Ctip2 regulates the growth, health, and correct function of this important neuron type in mice, toward new approaches for the treatment of injured or degenerating neurons in the cerebral cortex, the highest region of the brain, that connect to the spinal cord and are central to human ALS, SCI, HSP, PLS.