THE IDENTIFICATION OF MYOGENIC CELLS IN SKELETAL-MUSCLE, WITH EMPHASIS ON THE USE OF TRITIATED-THYMIDINE AUTORADIOGRAPHY AND DESMIN ANTIBODIES

The identification of myogenic precursor cells (mpc) is a key factor i n determining the early events in the myogenesis and regeneration of s keletal muscle. Although satellite cells have long been established as the providers of myoblastic cells, very little is really known (apart from their anatomical location in relation to muscle fibres and their ability to migrate) about the precise role of satellite cells in myog enesis. Numerous techniques for labelling mpc have been devised, but n one of these has proven to be completely reliable in firmly establishi ng the origin of myogenic cells. The use of tritiated thymidine to lab el DNA in proliferating mpc (which are not specifically distinguishabl e at the time) and the subsequent location of their labelled progeny i n myotube nuclei has revealed a great deal of data on the timing of my ogenesis, but not about the nature of mpc themselves. DNA synthesis ca n also be detected by antibodies to the thymidine analogue, bromodeoxy uridine, and also by antibody staining for proliferating nuclear cell antigen. Like tritiated thymidine, these other markers are not specifi c for muscle but are general markers for DNA synthesis. In situ hybrid isation of various muscle-specific genetic markers and their products has been informative, as has immunolabelling of myogenin, MyoD1 and de smin. Desmin labelling has been particularly instructive in identifyin g mpc because it is one of the first muscle-specific proteins to be pr oduced in mpc. This review covers some of the techniques mentioned abo ve and their usefulness in determining the early events in myogenesis.