Analysis of Pax7 expressing myogenic cells in zebrafish muscle development, injury, and models of disease.

The transcription factor Pax7 is a marker and regulator of muscle progenitors and satellite cells that contribute to the embryonic development and postembryonic growth of skeletal muscle in vertebrates, as well as to its repair and regeneration. Here, we identify Pax7(+ve) myogenic cells in the zebrafish and characterize their behavior in postembryonic stages. Mononucleate Pax7(+ve) cells can first be found associated with myofibers at 72 hours post fertilization (hpf). To follow the behavior of muscle progenitor cells in vivo, we generated transgenic lines expressing fluorescent proteins under the control of the pax7a or pax3a promoters. We established an injury model using cardiotoxin injection and monitored cell proliferation and myogenic regulatory factor expression in myogenic precursors cells and muscle fibers after injury using proliferation markers and the transgenic lines. We also analyzed Pax7(+ve) cells in animals with dystrophic phenotypes and found an increased number compared with wild-type.