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。该系统在一生中经历重塑，并显示出从肌肉干细胞库中再生的非凡能力。然而，肌肉再生能力随着年龄的增长而下降。本研究的重点是确定小鼠生命周期中肌肉干细胞的起源和作用。我们建议使用敲入等位基因用Cre-ERT2融合基因（Pax7CE等位基因）代替Pax7，用于他莫昔芬（tmx）诱导细胞谱系追踪，目的如下：目标1：胚胎发生期间的Pax7谱系：我们将使用Pax7CE等位基因确定：1)Pax7+胚胎细胞何时何地成为命运受限的肌肉谱系？2) Pax7+胚胎细胞何时接受卫星细胞的命运？3)胚胎衍生的Pax7后代细胞能否产生具有肌肉再生能力的成体卫星细胞？目标2:Pax7在成人肌肉中的谱系：我们将进一步问：1)在强制运动后，Pax7+细胞是否被激活并融合到现有的肌纤维中？2) Pax7+细胞在成年期被白喉毒素（DTA）基因吞噬后，急性损伤后肌肉是否能维持大量稳态和/或再生？目的3：衰老肌肉中的Pax7谱系：衰老（小鼠为bb0 - 2岁）肌肉再生能力差，纤维化和脂肪细胞积聚。我们设计实验来问：1)成年卫星细胞有多安静？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Pax7+卫星细胞是否转化为成纤维细胞或脂肪细胞？

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?