Cell-cell interaction modulates myoD-induced skeletal myogenesis of pluripotent P19 cells in vitro

P19 embryonal carcinoma cells can be induced to differentiate in culture to develop into a wide variety of cell types that include skeletal muscle. Sk eletal myogenesis is controlled by transcription factors of the bHLH class, such as myoD. Expression of myoD from transfected genes did not induce sig nificant amounts of myogenesis in P19 cells and it was possible to establis h lines of undifferentiated P19[myoD] cells that express high levels of myo D mRNA. These P19[myoD] cells remained undifferentiated when cultured on so lid surfaces but when allowed to aggregate, P19[myoD] cells differentiated efficiently into skeletal muscle. Aggregation did not increase the amount o f myoD mRNA or the amount of myoD protein in P19[myoD] cells. The myoD prot ein was present in the nucleus in cells grown as attached or aggregated cul tures and, in both culture conditions, the myoD protein was associated with transcription factors of the E2A family and was able to bind DNA at E-box sequences. Thus, the aggregation-induced myogenesis of P19[myoD] cells occu rs in the absence of change in the myoD protein, suggesting that the cell-c ell contact achieved in aggregates may result in the induction of an activi ty that increases accessibility of the myoD transcription factor to muscle- specific genes in chromatin. (C) 1999 Academic Press.