Fig. 6. Fgf signaling is required for mesoderm induction by either EnR-Xema or Xema morpholinos. (A) EnR-Xema activity is inhibited by co-expression of a truncated Fgf receptor (XFD), but is not inhibited by expression of a truncated activin receptor (TAR). RT-PCR analysis of animal cap explants dissected at blastula stages and harvested during midgastrula stages. EnR-Xema RNA (1 ng), alone or with either 4 ng XFD or 4 ng TAR, was injected at early cleavage stages, as indicated. Activin (0.5 ng/ml) or Fgf (10 ng/ml) was added to stage 9 animal caps, as indicated. (B) XFD inhibits Xema morpholino-mediated Xbra and Xwnt8 expression. TAR did not inhibit Xbra or Xwnt8 expression in nine out of 12 independent trials. Neither TAR nor XFD inhibit dorsal endomesodermal (chordin) or endodermal (Sox17ß) marker induction by Xema morpholino injection; 4 ng TAR, 4 ng XFD, 10 ng MO-1 and 20 ng MO-2 were injected at early cleavage stages, as indicated.