Molecular profiling of gamma motor neuron development

描述（由申请人提供）：伽马运动神经元（g-MNs）是在大多数运动池中大量发现的功能和解剖学上不同的神经元亚类。这些“梭状运动”神经元专门支配肌纺锤体的束内纤维，并组成一个平行运动系统，独立于束外肌激活肌纺锤体纤维。控制g- mns的规范和分化的机制尚不清楚，也没有特异性的标记物被确定来区分g和早期发育的运动神经元。我们发现梭状运动神经元选择性地依赖于靶肌纺锤体来源的GDNF，最近的一项研究报道，梭状运动神经元在胚胎发生过程中也选择性地依赖于GDNF信号。使用这种营养需求作为功能标记，我们建议使用突变小鼠对g-MN选择性表达的基因进行差异筛选，其中g-MN前体在缺乏GDNF信号的情况下选择性丢失。我们还将在小鼠胚胎干细胞衍生的运动神经元培养中利用g-MNs的这一特性来分析g-MNs在体外的基因表达模式。最后，我们将使用在我们之前的工作中建立的分子和大小标准来选择性地分离出生后g- mn进行分子分析。鉴定g-MNs在不同发育阶段特异性表达的基因，将使利用分子遗传学方法研究梭状运动系统的形成和功能，包括其在正常运动行为和运动控制障碍中的作用成为可能。

DESCRIPTION (provided by applicant): Gamma motor neurons (g-MNs) are a functionally and anatomically distinct subclass of neurons found in large number in most motor pools. These "fusimotor" neurons exclusively innervate the intrafusal fibers of the muscle spindle and comprise a parallel motor system that activates muscle spindle fibers independently of extrafusal muscle. The mechanisms that control the specification and differentiation of g-MNs are unknown, and no specific markers have been identified to distinguish g from a motor neurons in early development. We have found that g fusimotor neurons are selectively dependent on target muscle spindle-derived GDNF, and a recent study reports that fusimotor neurons are also selectively dependent on GDNF signaling in embryogenesis. Using this trophic requirement as a functional marker, we propose to perform a differential screen for genes selectively expressed in g-MNs using a mutant mouse in which g- MN precursors are selectively lost in the absence of GDNF signaling. We will also exploit this specific property of g-MNs in cultures of mouse embryonic stem cell-derived motor neurons to profile the pattern of gene expression in g-MNs in vitro. Finally, we will use molecular and size criteria established in our previous work to selectively isolate postnatal g-MNs for molecular analysis. The identification of genes specifically expressed in g-MNs at different stages of development will make possible a molecular genetic approach to study the formation and function of the fusimotor system, including its role in normal motor behaviors and disorders of motor control. PUBLIC HEALTH RELEVANCE: Gamma motor neurons regulate sensory feedback to the central nervous system from the periphery by controlling the sensitivity of stretch receptors in skeletal muscle. Their function is critical for motor control and for our perception of where our limbs are in space. This study will provide a molecular profile of gamma motor neurons, opening the way to future study of this motor system in health and disease.