Fig. 4. The effect of FrdMO and DprMO on organizer markers. (A) Four-cell stage embryos were injected in the dorsal equatorial region of two blastomeres with morpholinos and mRNAs as indicated in Table 4, were cultured until stage 10.5 and were subjected to whole-mount in situ hybridization with organizer markers, chordin (left panels), Xnr3 (middle panels) and gsc (right panels) as probes. Co-injection of FrdMO and DprMO can reduce chordin and Xnr3 but not gsc, whereas ßcatMO strongly inhibited expression of all three genes, implying that Frodo and Dapper function in a gene-specific manner. The reduction of chordin and Xnr3 by co-injection of FrdMO and DprMO was reversed not only by Frodo RNA, but also ß-catenin RNA. (B) Four-cell stage embryos were injected in the equatorial region of each blastomere with morpholinos and mRNAs as indicated and were analyzed at stage 10 and 11 by RT-PCR, using primers specific for chordin, cerberus, Xnr3, siamois, gsc and vent1. EF1 primers were used to control loading.