Fig. 3

alk8 acts downstream of bmp2b and bmp7 and upstream of smad5. All embryos are shown at 36 hours post-fertilization, lateral view, head towards the left. The laf, swr and snh embryos shown in panels C-F,K,L were genotyped after photography. (A) Wild-type sibling. (B) laf^tm110 mutant. Arrows indicate absent ventral tail fin and enlarged pericardial cavity. (C) Rescued laf^tm110 mutant, injected with alk8 mRNA. (D) Rescued laf^tm110 mutant, injected with smad5 mRNA; arrow indicates starting swelling of the precardial cavity. (E) laf^tm110 mutant, injected with bmp2b mRNA. (F) laf^tm110 mutant, injected with bmp7 mRNA. Arrowheads indicate small head and enlarged blood islands, both signs for ventralization; arrows indicate absent ventral tail fin and enlarged heart cavity, both laf-characteristic features (compare with B). (G-J) Genetically wild-type embryos after injection with bmp2b mRNA (G), co-injection of bmp2b mRNA and the alk8 antisense morpholino oligonucleotide alk8morph2 (H), injection of smad5 mRNA (I), or co-injection of smad5 mRNA and alk8morph2 (J). The embryos in G,I,J display strong ventralization (V3; arrowheads indicate absent head and enlarged blood island); the embryo in H shows strong dorsalization (C4; arrow indicates wound-up trunk), similar to the alk8morph2-injected embryo shown in Fig. 2D. (K) Rescued bmp2b mutant swr^ta72, injected with alk8CA mRNA. (L) Rescued bmp7 mutant snh^ty68, injected with alk8CA mRNA. Arrows in K,L indicate reduced or absent ventral tail fin, indicating mild dorsalization (C1); arrowheads indicate smaller head, indicating weak ventralization. (M,N) Sibling embryos from sbn^dtc24 heterozygous mother; displaying C4 dorsalization, characterized by wound-up tail and trunk (arrows); (M) uninjected embryo; (N) alk8CA mRNA-injected embryo.