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. 1 ng of EnR-Xema RNA, alone or with either 4 ng XFD or 4 ng TAR, was injected at early cleavage stages, as listed. Activin (0.5 ng/mL) or FGF (10 ng/mL) were added to stage 9 animal caps, as listed. (B) XFD inhibits Xema morpholino-mediated Xbra and Xwnt8 expression; TAR did not inhibit Xbra and Xwnt8 expression in 9/12 independent trials. Neither TAR nor XFD inhibit dorsal endomesodermal (chordin) or endodermal (sox17β) 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 listed.