Stem cells don't come emblazoned with a label marked “progenitor,” and yet it was by appearance alone that Alexander Mauro identified satellite cells as a possible muscle stem cell (Mauro, 1961). It was the same year that the clonal nature of hematopoietic stem cells (HSCs) was proven by Till and McCulloch (1961). Mauro did not have proof for the nature of his stem cell, but rather some electron microscopy (EM) images that he felt “might be of interest to students of muscle histology and furthermore, as we shall suggest, might be pertinent to the vexing problem of skeletal muscle regeneration.”
The problem was vexing because of the syncytial nature of muscle. Any tear of a muscle fiber would expose all the nuclei of a multinucleate myofiber to the unfriendly extracellular environment. Earlier investigators suggested that these nuclei might “gather up” cytoplasm and membrane around themselves...
