HETEROGENEITY IN THE PROGENY OF SINGLE HUMAN MUSCLE SATELLITE CELLS

We examined whether freshly isolated (native) human muscle satellite c ells (HMSC), as well as their proliferating clonal progenies, were het erogeneous. We studied the expression of the cytoskeletal proteins, de smin (DSM), alpha-sarcomeric and alpha-smooth muscle actins (alpha-SR actin, alpha-SM actin), three markers that may be expressed prior to t he fusion process. We found that native HMSC constituted a homogeneous population of cells expressing desmin and giving rise to similar clon es in vitro. The clonal progeny of HMSC was heterogeneous, including s everal subpopulations of myoblasts with different cytoskeletal phenoty pes, commitment states and fusion abilities. A major subpopulation tha t expressed both alpha-sarcomeric actin and desmin during the prolifer ative stage corresponded to a ''predifferentiated'' population of myob lasts, committed to fusion. Another subpopulation, expressing exclusiv ely desmin, and phenotypically similar to native HMSC, failed to fuse under fusion-promoting conditions and could represent a new generation of HMSC born in culture.