MyoD-positive myoblasts are present in mature fetal organs lacking skeletal muscle

The epiblast of the chick embryo gives rise to the ectoderm, mesoderm, and endoderm during gastrulation. Previous studies revealed that MyoD-positive cells were present throughout the epiblast, suggesting that skeletal muscle precursors would become incorporated into all three germ layers. The focus of the present study was to examine a variety of organs from the chicken f etus for the presence of myogenic cells. RT-PCR and in situ hybridizations demonstrated that MyoD-positive cells were present in the brain, lung, inte stine, kidney, spleen, heart, and liver. When these organs were dissociated and placed in culture, a sub-population of cells differentiated into skele tal muscle. The G8 antibody was used to label those cells that expressed My oD in vivo and to follow their fate in vitro. Most, if not all, of the musc le that formed in culture arose from cells that expressed MyoD and G8 in vi vo. Practically all of the G8-positive cells from the intestine differentia ted after purification by FACS((R)). This population of ectopically located cells appears to be distinct from multipotential stem cells and myofibrobl asts. They closely resemble quiescent, stably programmed skeletal myoblasts with the capacity to differentiate when placed in a permissive environment .