FIGURE 3.

Phenotypic rescue of α-SE morpholino provided by repression of Su(H) mRNA. (A) Design of a “rescue” experiment. In control embryos (upper panel), Su(H) mRNA is bound by CUGBP1, leading to a rapid degradation of the mRNA. The α-SE morpholino (middle panel) prevents CUGBP1 binding to Su(H) mRNA, hence stabilizes it, leading to protein overexpression. It also leads to phenotypic defects. If these phenotypic defects are specifically due to the derepression of Su(H) mRNA, then development should be restored by injecting an adequate amount of a second morpholino directed against the translation initiation region (α-SAUG, lower panel), which, by reducing translation, will reduce the amount of Su(H) protein to a normal level. (B) Quantification of segmentation defects. Embryos were co-injected with the indicated amounts of α-SE morpholino and 0, 10, 60, or 100 fmol of α-SAUG. Embryos were sorted at stage 24–26 according to their phenotype: unaffected (like in Fig. 2C, black), mild (like in Fig. 2D, dark gray), or strong (like in Fig. 2E, light gray). The total number of sorted embryos for each combination of morpholinos is indicated. (C,D) Xenopus embryos at the two-cell stage were injected in each blastomere with 2 pmol of control morpholino (lane 1) or 2 pmol of α-SE morpholino in the absence (lane 2) or the presence (lane 3) of 60 fmol of α-SAUG morpholino. They were allowed to develop until the tailbud stage (24–26). RNA (C) and protein (D) levels were analyzed as in Figure 2, A and B.