Genetic Control of Phrenic Motor Neuron Development and Maintenance

呼吸是陆生脊椎动物最基本的运动行为。的频率和振幅 呼吸运动由位于脑干和脊髓中的神经网络控制。在哺乳动物中， 在吸气期间，横隔膜肌肉的收缩对于驱动气流进入肺部是必不可少的。尽管 由于调节呼吸节律的神经网络的复杂性，横膈膜的收缩是由一个 单一运动输入，颈部膈运动柱（PMC）内运动神经元（MN）的活动 脊髓PMC神经元的丧失是退行性MN疾病（如 肌萎缩侧索硬化症（ALS）和脊髓损伤。尽管它们起着重要的作用， PMC神经元身份的决定因素在很大程度上是未知的。我们发现PMC神经元的发育 需要Hox5转录因子的持续活性。MN中缺乏Hox5基因的小鼠死于呼吸道感染 出生时失败，并在PMC身份的多个方面表现出缺陷，包括细胞体位置，轴突导向， 和横膈膜神经支配。在这个建议中，我们将研究Hox 5基因在决定和 维持膈神经的同一性。 在目的1中，我们将确定Hox 5蛋白在膈神经MN中的时间上不同的功能，以及膈神经MN如何 在整个生命周期中保持同一性。 在目标2中，我们将定义Hox5基因如何在转录水平上控制膈MN的特化。 在目标3中，我们将确定直接的Hox5效应子，并剖析其调控机制。 我们已经开发了一种综合方法，包括遗传模型，高通量测序， 电生理学和行为测定，如体积描记术，以解决这些问题在体内。的 本提案的首要目标是揭示膈神经元规范的基本原则， 这样我们就可以开始考虑呼吸功能障碍的替代治疗方法。

Breathing is the most fundamental motor behavior for terrestrial vertebrates. The frequency and amplitude of breathing movements are controlled by neural networks residing in the brainstem and spinal cord. In mammals, contraction of the diaphragm muscle is essential for driving airflow into the lungs during inspiration. Despite the complexity of the neural networks that regulate respiratory rhythms, diaphragm contraction is controlled by a single motor input, the activity of motor neurons (MNs) within the Phrenic Motor Column (PMC) in the cervical spinal cord. Loss of PMC neurons is the primary cause of death in degenerative MN diseases such as amyotrophic lateral sclerosis (ALS) and spinal cord injuries. Despite their essential role, the molecular determinants of PMC neuron identity are largely unknown. We have found that the development of PMC neurons requires the sustained activity of Hox5 transcription factors. Mice lacking Hox5 genes in MNs die of respiratory failure at birth and exhibit defects in multiple aspects of PMC identity, including cell body position, axon guidance and diaphragm innervation. In this proposal we will investigate the function of Hox5 genes in determining and maintaining phrenic MN identity. In Aim 1 we will determine temporally distinct functions of Hox5 proteins in phrenic MNs and how phrenic MN identity is maintained throughout lifetime. In Aim 2 we will define how Hox5 genes control phrenic MN specification at the transcriptional level. In Aim 3 we will identify direct Hox5 effectors and dissect their regulatory mechanisms. We have developed an integrative methodology encompassing genetic models, high-throughput sequencing, electrophysiology and behavioral assays, such as plethysmography, to address these questions in vivo. The overarching goal of this proposal is to uncover the basic principles underlying phrenic MN specification and maintenance so that we can begin to consider alternative treatment methods for respiratory dysfunction.