Fig. 4

Nodal signaling is required for maintenance, but not initiation, of dpr1 expression. Embryos were probed for zebrafish dpr1. A-L: MZoep mutant embryos. M-X: Wild-type control embryos. Developmental stages are indicated. C,D: Arrowheads indicate decreased dpr1 expression in MZoep mutant embryos. O,P: Arrowheads indicate dorsal dpr1 expression in wild-type embryos. E-J: Arrows indicate ectodermal dpr1 expression. A,C,E,G,I,K,M,O,Q,S,U,W are lateral views. B,D,F,H,N,P,R,T are animal views. Dorsal is to the right, except in J,L,V,X, which are dorsal views. In J,L,V,X, anterior is upward. Note that, because later epiboly (epib.) movements are delayed in MZoep embryos, dpr1 expression in MZoep embryos at 70% and 90% epiboly is compared with wild-type embryos at 90% epiboly and tail bud stages, respectively.