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?
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.
|Choi, Moon-Chang; Ryu, Soyoung; Hao, Rui et al. (2014) HDAC4 promotes Pax7-dependent satellite cell activation and muscle regeneration. EMBO Rep 15:1175-83|
|Minchin, James E N; Williams, Victoria C; Hinits, Yaniv et al. (2013) Oesophageal and sternohyal muscle fibres are novel Pax3-dependent migratory somite derivatives essential for ingestion. Development 140:2972-84|
|Blum, Jordan M; Ano, Leonor; Li, Zhizhong et al. (2013) Distinct and overlapping sarcoma subtypes initiated from muscle stem and progenitor cells. Cell Rep 5:933-40|
|Gunther, Stefan; Kim, Johnny; Kostin, Sawa et al. (2013) Myf5-positive satellite cells contribute to Pax7-dependent long-term maintenance of adult muscle stem cells. Cell Stem Cell 13:590-601|
|Lepper, Christoph; Fan, Chen-Ming (2012) Generating tamoxifen-inducible Cre alleles to investigate myogenesis in mice. Methods Mol Biol 798:297-308|
|Havis, Emmanuelle; Coumailleau, Pascal; Bonnet, Aline et al. (2012) Sim2 prevents entry into the myogenic program by repressing MyoD transcription during limb embryonic myogenesis. Development 139:1910-20|
|Kim, Youngjo; Sharov, Alexei A; McDole, Katie et al. (2011) Mouse B-type lamins are required for proper organogenesis but not by embryonic stem cells. Science 334:1706-10|
|Lepper, Christoph; Partridge, Terence A; Fan, Chen-Ming (2011) An absolute requirement for Pax7-positive satellite cells in acute injury-induced skeletal muscle regeneration. Development 138:3639-46|