Fig. 1

tbx16/spadetail dsRNA injection into zebrafish embryos appears to cause a mosaic phenocopy of the spadetail mutation. Embryos in (b–d, h) are viewed from the animal pole, and those shown in (f, g) are viewed from the dorsal side. (a) Regions of the spadetail mRNA used to produce nonoverlapping antisense riboprobe and ss or dsRNA transcripts. (b–d) Expression of endogenous spt mRNA in response to injection of tbx16/spt dsRNA. Embryos are shown in animal pole view at the 40% epiboly stage after in situ hybridization with a riboprobe specific for the portion of the tbx16/spt transcript encoding the T-box. (b) Embryos injected with 40 pg tbx16/spt dsRNA; sectors devoid of endogenous spt mRNA are highlighted with arrowheads. (c) Expression of endogenous spt in the wild-type embryo (wt) and widespread loss in the spt mutant embryo (spt) at 40% epiboly. (d) Endogenous tbx16/spt expression at 40% epiboly is unaffected by injection of antisense tbx16/spt ssRNA corresponding to the same region of the mRNA used to generate dsRNA. (e) Dose response to tbx16/spt dsRNA injection measured by depletion of endogenous tbx16/spt mRNA at 40% epiboly. Different concentrations of RNA were injected into embryos at a constant volume. Between 20 and 56 embryos were used for each concentration point. (f) Formation of anterior trunk somites in response to tbx16/spt dsRNA. Embryos at the 3-somite stage, showing normal somite boundary formation, denoted with arrowheads in wild-type, uninjected embryos (wt), unilateral loss of anterior somites in tbx16/spt dsRNA-injected embryos (dsRNA), and complete lack of somites in spt mutant embryos (spt). (g) Expression of red blood cell marker gata1 in 10-somite embryos, showing normal primitive blood in wild-type, uninjected embryos and a depletion of gata1-expressing cells along the lateral plate mesoderm (arrowheads) in tbx16/spt dsRNA-injected embryos. (h) Expression of prospective paraxial mesoderm marker papc at 50% epiboly with dorsal to the top, showing radial expression in the margin in wild-type, uninjected embryos, disrupted marginal expression in tbx16/spt dsRNA-injected embryos, and an absence of papc in the margin in spt mutant embryos.