Fig. 6. Initiation of MyoD expression in vitro. (A,D) Culture of isolated presomitic mesoderm for 3-4 hours. (A) Delta1 (n=30), (B) Myf5 (n=55), (C) Wnt5b (n=67) and (D) Fz7 (n=8) were autonomously expressed in these conditions. (E,P). Culture of dissociated rostral presomitic mesoderm cells. Note that the same results were obtained in six independent experiments. In these experimental conditions, MyoD (F), Wnt5b (G), Fz7 (H), Paraxis (O) and Myf5 (P) are expressed. Pax1 (E) and Shh (M) serve as negative controls. When dissociated presomitic mesoderm cells are cultured in the presence of supernatant from Bmp4-expressing cells, initiation of MyoD expression is not observed (N). When Shh is added to dissociated presomitic cells, expression of MyoD (J), Wnt5b (K) and Fz7 (L) is strongly enhanced, while Pax1 (I) expression is activated.