Fig. 4. Ras-dva functioning is essential for the development of the head structures. (A) The head of control tadpole, as seen from the dorsal side. (B) The head of a tadpole developed from the embryo microinjected with the anti-Ras-dva morpholino oligonucleotides (MO) into the right blastomere at the two-cell stage. As a result of inhibition of translation of the Ras-dva mRNA by the morpholino, the tadpole has a reduced eye, telencephalon, olfactory pit and otic vesicle. (C) The head of the tadpole developed from the embryo microinjected by dnRas-dvaT22N mRNA into the right blastomere at the two-cell stage. The malformations are similar to those described above that were caused by anti-Ras-dva MO microinjections. This indicates that the dnRas-dvaT22N construct works. (D,E) The rescue experiment. Co-injection of anti-Ras-dva MO with synthetic Ras-dva mRNA lacking the MO binding sequence (E) is able to rescue the effects of anti-Ras-dva morpholino oligonucleotides (D).