Fig. 4. Tlr suppresses Sog gain-of-function activities in vivo. (A) Injections of sog mRNA in one of the ventral four-cell stage blastomeres of Xenopus embryos induces secondary axis formation (red arrowheads) in tadpoles shown at development stages 19 and 28. Co-injection of tld and tlr inhibit Sog-mediated secondary axis formation. To ensure equimolecular amounts of mRNA, we used 2 ng capped mRNA for sog and tld and 4 ng for tlr, which had a transcript approximately twice as long as tld because of the longer pro-peptide and UTR sequences. (B) Wing phenotypes produced by ectopic expression of Sog and Tsg are suppressed by addition of activated Tld (atld) (UAS-tld27) or wild-type Tlr (tlr) (UAS-tlr3).