Molecular Mechanisms of CTIP2 Function in Corticospinal Motor Neuron Development

7.项目总结/摘要 拟议实验的长期目标是阐明分子遗传学对基因表达的控制。 皮质脊髓运动神经元（CSMN）的神经元亚型特异性发育（以及相关的新皮质 投射神经元），并潜在地使未来的方法能够修复退化或损伤的CSMN。 CSMN是所有新皮层投射神经元的发育原型，并且在临床上重要， 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， 其轴突损伤是脊髓损伤中运动功能丧失的中心。拟议的实验将深入 研究中枢重要的CSMN/脑下特异性转录因子CTIP 2（COUP-TF）的功能 相互作用蛋白2）及其辅基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发展和连接的关键调节器， 作为多投射神经元亚型分化调节（主要是抑制）的共同靶点 途径。已知Ctip 2在其他器官系统中参与发育谱系特化 决策在新皮质内，CTIP 2由CSMN和相关的大脑下投射特异性表达 神经元，并且是CSMN轴突的生长、成束和靶向所必需的。虽然Ctip 2 虽然CSMN的发展已经成为重要的核心，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确定为一种 关键的CSMN分子控制，并证明Ctip 2-/-小鼠中的CSMN轴突之前被错误路由 穿透内囊（IC），在IC中解束，并且不能投射到脊髓（SC）。 由于CTIP 2还控制纹状体中型多刺神经元（MSN）的分化，MSN围绕着CTIP 2。 CSMN轴突在IC中，这一假设表明，Ctip 2-/- CSMN连接到SC的一些缺陷 可能由Ctip 2-/- MSN中轴突生长和导向控制的失调引起。仅缺乏Ctip 2的小鼠 在新皮层（Emx 1-Cre; Ctip 2fl/fl）中，CSMN一个子集进入IC并在IC中成束，有些甚至 其他的初步研究发现Ctip 2与Ctip 1相互作用是交叉抑制的 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：（目标1，2）描绘CSMN自治和非CSMN自治的角色 Ctip 2在CSMN轴突生长和成束中的作用;（目的3，4）研究一种新鉴定的遗传交叉- Ctip 2和Ctip 1在CSMN发育中的抑制性相互作用，以及独立作用 Ctip 1在其他深层投射神经元的区域组织和发育中的作用。实验超越 这一提议可以鉴定CSMN中由Ctip 2直接或间接调控的基因。这些研究将阐明 Ctip 2是CSMN分化的中心调节因子，它单独或与其他基因一起作用， 指导这种发育上典型的、临床上重要的神经元类型的发育的精确性。

7. PROJECT SUMMARY / ABSTRACT 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 project 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.