Muscle Stem Cell Lineage

描述（由申请人提供）：哺乳动物的肌肉组织为运动提供机械力。该系统在整个生命周期中经历重塑，并显示出从肌肉干细胞库再生的非凡能力。然而，肌肉的再生能力随着年龄的增长而下降。该提案的重点是定义肌肉干细胞在小鼠寿命期间的起源和作用。我们提出使用敲入等位基因用Cre-ERT 2融合基因（Pax 7 CE等位基因）替换Pax 7用于他莫昔芬（tmx）诱导的细胞谱系追踪，目的1：胚胎发生期间的Pax 7谱系：我们将使用Pax 7 CE等位基因来确定：1）何时和何处Pax 7+胚胎细胞成为肌肉谱系的命运限制性的？2)Pax 7+胚胎细胞何时会成为卫星细胞？3)胚胎来源的Pax 7后代细胞能产生能够肌肉再生的成体卫星细胞吗？目的2：成人肌肉中的Pax 7谱系：我们将进一步问：1）在强迫运动后，Pax 7+细胞是否被激活并融合到现有的肌纤维中？2)当Pax 7+细胞在成年期被白喉毒素（DTA）基因消融时，肌肉能否在急性损伤后保持质量的稳态和/或再生？目的3：衰老肌肉中的Pax 7谱系：衰老（对于小鼠> 2岁）肌肉再生不良，并积累纤维化和脂肪细胞。我们设计实验来问：1）成年卫星细胞有多静止？2)老年卫星细胞是不同于年轻人的干细胞群吗？3)损伤后衰老的Pax 7+卫星细胞转化为成纤维细胞或脂肪细胞吗？ 公共卫生相关性：小鼠的发育和体外研究表明Pax 7是卫星细胞（假定的肌肉干细胞）的主要调节因子。我们计划使用新开发的遗传工具来定义Pax 7表达细胞在小鼠胚胎发育过程中的谱系，在运动后的成年肌肉中，以及在损伤后的衰老肌肉中。肌肉干细胞具有改善肌营养不良症的治疗潜力。我们的研究将为了解体内卫星细胞的基本生物学提供补充知识。

DESCRIPTION (provided by applicant): The mammalian musculature provides mechanical force for locomotion. This system undergoes remodeling throughout lifetime and displays remarkable ability to regenerate from reservoirs of muscle stem cells. However, the muscle regenerative capacity declines with age. This proposal focuses on defining the origin(s) and roles of muscle stem cells during the life span of a mouse. We propose to use a knock-in allele replacing Pax7 with the Cre-ERT2 fusion gene (the Pax7CE allele) for tamoxifen (tmx) inducible cell lineage tracing in following aims: Aim 1: Pax7 lineage during embryogenesis: We will use the Pax7CE allele to determine: 1) When and where do Pax7+ embryonic cells become fate-restricted to the muscle lineage? 2) When do Pax7+ embryonic cells take on a satellite cell fate? 3) Do embryonically derived Pax7 descendant cells give rise to adult satellite cells capable of muscle regeneration? Aim 2: Pax7 lineage in adult muscles: We will further ask: 1) After forced exercise, do Pax7+ cells become activated and fuse into existing myofibers? 2) When Pax7+ cells are genetically ablated by diptheria toxin (DTA) in adulthood, can muscle maintain homeostasis in mass and/or regenerate after acute injury? Aim 3: Pax7 lineage in aged muscles: Aged (> 2 year old for a mouse) muscles are poor in regeneration and accumulate fibrosis and adipocytes. We design experiments to ask: 1) How quiescent are adult satellite cells? 2) Are aged satellite cells a different population of stem cells from those of young adults? 3) Do aged Pax7+ satellite cells trans-fate into fibroblasts or adipocytes after injury? PUBLIC HEALTH RELEVANCE: Developmental and in vitro studies in the mouse have implicated Pax7 as a master regulator for satellite cells, the presumed muscle stem cell. We plan to use newly developed genetic tools to define the lineage of Pax7 expressing cells during mouse embryogenesis, in the adult muscle after exercise, and in the aging muscle after injury. Muscle stem cells have the therapeutic potential in ameliorating muscular dystrophies. Our research will provide complimentary knowledge to understand the basic biology of satellite cells in vivo.