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皮质脊髓运动神经元（CSMN）（以及相关的新皮质投射神经元）神经元亚型特异性发育的分子遗传控制，并潜在地使未来的方法能够修复退化或受损的CSMN。CSMN既是所有新皮质投射神经元的发育原型，也是临床上重要的脑神经元，在肌萎缩侧索硬化症/运动神经元疾病（ALS/MND）中退行性变，其轴突损伤是脊髓损伤中运动功能丧失的核心。拟开展的实验将深入研究CSMN/脑下特异性转录因子CTIP2 （COUP-TF相互作用蛋白2）及其平行物CTIP1在小鼠新皮层CSMN及相关神经元发育中的作用。Ctip2作为CSMN发育和连通性的关键调节因子，以及多种投射神经元亚型分化途径调节（主要是抑制）的共同靶点，越来越多地出现。从其他器官系统中，我们知道Ctip2参与了发育谱系规范的决定。在新皮层内，CTIP2在CSMN和相关的脑下投射神经元中特异性表达，是CSMN轴突生长、束控和靶向所必需的。虽然Ctip2对CSMN的发展至关重要，但其功能的大多数方面仍然未知。大量初步数据支持这些目标。本实验室之前的工作确定了Ctip2是CSMN的关键分子控制，并证明Ctip2-/-小鼠的CSMN轴突在穿透内囊（IC）之前路径错误，在IC中去血循环，并且不能投射到脊髓（SC）。由于CTIP2还控制着CSMN轴突周围纹状体中等棘神经元（MSN）的分化，因此我们提出了CTIP2 -/- CSMN与SC连接的一些缺陷可能是由于CTIP2 -/- MSN轴突生长和引导控制失调所致。仅在新皮层缺乏Ctip2的小鼠（Emx1-Cre;Ctip2fl/fl）发现CSMN的一个子集进入IC并束状，有些甚至到达SC。其他初步研究发现Ctip2平行Ctip1与Ctip2交叉抑制相互作用，控制深层投射神经元的发育，Ctip1还调节区域组织。拟议的实验将：（目标1,2）描述CSMN自主和非CSMN自主Ctip2在CSMN轴突生长和束化中的作用；（目的3,4）研究一种新发现的基因交叉抑制相互作用

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.