Figure 4.

Pax3, Dach2, and MyoD are regulated by signals from the ectoderm. (A–D) Whole-mount in situ hybridizations of embryos 24–36 hr after barrier placement between the somite and the dorsal ectoderm. Embryos at stage 16–19. The region covered by the barrier is indicated with a red bracket. (E,F) Paraffin sagital sections of the embryos shown in A–D at the position indicated by the blue arrows in A–D. (A,E) Pax3; (B,F) Dach2; (C,G) MyoD; (D,H) Pax1. Blue arrows in E–H point to the lateral edge of the somite where expression of Pax3, Dach2, and MyoD is lost and where Pax1 expression is expanded.