RNAi inhibition of Pax3/7 expression leads to markedly decreased expression of muscle determination genes.

Skeletal muscle regeneration by cell transplantation for the treatment of muscle diseases requires the identification and isolation of well-defined, early skeletal muscle progenitor cells. It is known that myogenesis is governed by the sequential and compound activation of the muscle determination genes, the myogenic regulatory factors (MRFs). Recently it has been proposed that the transcription factors Pax3 and Pax7 trigger the expression of the MRFs and thereby specify a novel population of cells destined to enter the myogenic program. We directly tested this hypothesis using RNA interference methodology to reduce the levels of Pax3 and Pax7 RNA in mouse embryoid bodies developing in vitro. We found that decreasing the levels of Pax3/Pax7 RNA leads to a marked and selective decrease in Myf5, MyoD and Desmin expression. Pax3 and Pax7 expressing cells from developing embryos may thus serve as the earliest known skeletal muscle progenitor cells potentially useful for cell transplantation studies.