Fig. 4

tarMR interferes with the formation of anterior midline structures. Wild-type embryos were either left uninjected or injected with tarMR RNA (MR) alone or with wild-type tar RNA (MR + tar) at the 16-cell stage into one marginal blastomere. The phenotypes of the embryos were analysed at 24–30 hpf, either on live embryos (A–C, frontal head view) or by in situ hybridisation (D–F, lateral view, anterior to the left) with the ventral CNS marker shh. (A–C) Overexpression of tarMR leads to cyclopia in 11% (n = 95) of tarMR-injected embryos (B) which can be rescued (C, remaining cyclopic embryos 3%, n = 75) by coexpression of wild-type tar RNA. (D–F) Similarly, overexpression of tarMR leads to the downregulation of shh in 12% of tarMR-overexpressing embryos in the ventral brain (E, n = 95). This phenotype was rescued by adding 100 pg of tar RNA (F).