The identification of myogenic precursor cells (mpc) is a key factor
in determining the early events in the
myogenesis and regeneration of skeletal 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 myogenesis. Numerous
techniques for labelling mpc have been devised, but none of these has
proven to be completely reliable in
firmly establishing the origin of myogenic cells. The use of tritiated
thymidine to label DNA in proliferating
mpc (which are not specifically distinguishable at the time) and the
subsequent location of their labelled
progeny in myotube nuclei has revealed a great deal of data on the
timing of myogenesis, but not about the
nature of mpc themselves. DNA synthesis can also be detected by antibodies
to the thymidine analogue,
bromodeoxyuridine, and also by antibody staining for proliferating nuclear
cell antigen. Like tritiated
thymidine, these other markers are not specific for muscle but are general
markers for DNA synthesis. In
situ hybridisation of various muscle-specific genetic markers and their
products has been informative, as has
immunolabelling of myogenin, MyoD1 and desmin. Desmin labelling has
been particularly instructive in
identifying mpc because it is one of the first muscle-specific proteins
to be produced in mpc. This review
covers some of the techniques mentioned above and their usefulness in
determining the early events in myogenesis.