Interaction between sub-dorsalizing tsg1 knockdown and swirl (bmp2b) heterozygotes. All embryos were injected with 16 ng tsg1 MO. At 24 hpf, an injected wild-type embryo was not dorsalized (A), whereas injected swirl (bmp2b) heterozygous siblings were dorsalized. The extent of dorsalization was categorized as follows: (B) weak, class 1 (arrowhead indicates partial loss of the ventral tail fin); (C) moderate, class 3; and (D) strong, class 4. (E-J) Whole-mount in situ hybridization of myod, pax2a and krox20 in 16 ng tsg1 MO1 injected embryos at the eight-somite stage. Injected wild-type embryos were not affected (E,F), whereas heterozygotes displayed a range of dorsalizations (G,H, moderate; I, strong; J, stronger). (F,H) More posterior views of the same embryos shown in E,G, respectively. (J) The somites extend around the circumference, which is typical of a strong, class 4 dorsalization.