The Phos-A but not the A-mut peptide induces axis duplication and Xnr3 expression in Xenopus embryos.
A, B, C, D. Uninjected embryo (A), A-mut-injected embryo (B), and Phos-A-injected embryo (C) shown at neural fold stage. The duplicated partial axis is labeled by the red arrowhead. Ventrally injected Phos-A (4.8 ng/embryo) induced axis duplication in 19% embryos (10 of 52). A-mut (4.8 ng/embryo) did not induce axis duplication (0 of 60). Three independent experiments were combined (D). E. Phos-A (3 and 4.8 ng/embryo) but not A-mut (4.8 ng/embryo) induced Xnr3 expression in animal pole explants, as assayed by RT-PCR. Xenopus Wnt8 RNA injection (8 pg/embryo) served as a positive control. The activity of the Phos-A peptide was significantly weaker than that of Wnt8 RNA, likely due to dilution, proteolysis and/or dephosphorylation in the embryo in the absence of any de novo synthesis. WE: whole embryo. EF1-a: loading control. –RT: without reverse transcriptase.