Embryos were injected at the one cell stage with 100 pg of tbx2a-gfp (A-D) or tbx2b-gfp (E-F) RNA which leads to strong fluorescence throughout the embryo at 24 hpf (A, C, E). This signal is completely blocked by co-injection of MO2a (B) or MO2ab (D, F). Note that the previously validated MO2b is not used in this assay, because it is a splice-blocker. However, MO2a does not block expression of the tbx2b-gfp transcript (not shown). For each sample n>25.