Migration of adult myogenic precursor cells as revealed by GFP/nLacZ labelling of mouse transplantation chimeras

We studied the migratory behaviour of adult muscle precursor cells in the mouse into and from skeletal muscle grafts using green fluorescent protein (GFP) and nuclear LacZ transgenes as complementary and double markers of the cell's origin. Owing to the small molecular mass and extreme solubility of GFP, this label provided a drastically increased sensitivity for detection compared with the markers that had been used previously. During the first six weeks after the operation, the graft/host border was well defined, with only occasional local intermingling and co-fusion of host and donor myogenic cells. Seven to eleven weeks after the operation we found that the host myogenic cells had migrated into the graft, and graft myogenic cells had migrated into the adjacent host muscle, with integration of donor nuclei into pre-existing myotubes or muscle fibres. There was no indication of an origin of, or target for, these myogenic cells besides neighbouring muscles. Our observations indicate migration of these cells through solid muscle tissue, over a distance of several millimetres. The migratory activity of adult myogenic precursor cells can be stimulated by traumatic events in either the target muscle or the muscle of origin.