ISH of drug and/or MO-treated embryos. (A) In 10 µM SU5402-treated wild-type embryos, tbxta and tbx16 transcripts are decreased (arrows) at 80% epiboly, but almost normal at 6ss. Both transcripts are absent in 30 µM SU5402-treated embryos at 6ss. (B) Adaxial myod expression (black arrowheads) is completely ablated in tbxta or tbx16 morphants at 80% epiboly, and myf5 expression is greatly decreased (black arrowheads). fgf8a mRNA is ablated in the posterior notochord of tbxta morphants (blue arrowheads), but upregulated in tbx16 morphants around the germ marginal zone at 80% and in the posterior notochord at 6ss (yellow arrowheads). Expression of fgf3 and fgf4 is absent in posterior notochord of tbxta morphants, but enhanced in that location in tbx16 morphants (green arrowheads). (C) At 6ss, pre-adaxial myod expression (black arrowheads) is lost in tbxta morphant tailbud, and diminished in tbx16 morphants. Injection of tbx16 MO, but not tbxta MO, reduces adaxial myf5 mRNA to the level observed in paraxial mesoderm (orange arrowheads), whereas tbxta MO but not tbx16 MO upregulates myf5 mRNA in the posterior tailbud (asterisks). Tbx16 MO abolishes pre-adaxial myf5 mRNA in cyA-treated embryos (white arrowheads). Adaxial myf5 and myod transcripts recover in tbxta morphants, but are ablated by cyA-treatment (red arrowheads). CyA-treatment of tbx16 morphants ablates adaxial myod expression throughout the axis (cyan arrowheads), leaving only residual paraxial myod and myf5 expression (pink arrowheads). Scale bars: 100 µm.
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