Muscle Stem Cell Lineage

描述(申请人提供)：哺乳动物的肌肉系统为运动提供机械力。这个系统在一生中都会经历重塑，并显示出从肌肉干细胞库中再生的非凡能力。然而，肌肉的再生能力随着年龄的增长而下降。这项提议的重点是确定肌肉干细胞的起源(S)和在小鼠生命周期中的作用。我们建议用Cre-ERT2融合基因(Pax7CE等位基因)取代Pax7来追踪他莫昔芬(TMX)诱导的细胞谱系，目的如下：目的1：在胚胎发生过程中，Pax7的谱系：我们将使用Pax7CE等位基因来确定：1)Pax7+胚胎细胞何时何地成为命运受限于肌肉谱系的细胞？2)Pax7+胚胎细胞何时承担卫星细胞的命运？3)胚胎来源的Pax7后代细胞是否产生能够肌肉再生的成年卫星细胞？目的2：PAX7在成年肌肉中的谱系：我们将进一步问：1)强迫运动后，Pax7+细胞是否被激活并融合到现有的肌纤维中？2)成年后白喉毒素(DTA)基因去除Pax7+细胞时，肌肉能否维持体内平衡和/或急性损伤后再生？目的3：PAX7在老年肌肉中的谱系：老年(对小鼠来说是2岁)肌肉再生能力差，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)衰老的卫星细胞是不同于年轻人的干细胞群吗？3)老化的Pax7+卫星细胞在损伤后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?