Fig. 3. Tcf1 and Lef1 are required for ventrolateral mesoderm development. Vegetal view of Xpo (A-O) and XmyoD (A'-O') expression in stage 10.5 embryos, dorsal towards the top, injections into the right side. Xpo and XmyoD expression are not affected by injection of 60 ng control MO (B,B') or Tcf4 MO (C,C'), but are both significantly downregulated by injection of 60 ng Tcf3 MO (D,D'), 20 ng Tcf1 MO (F,F') or 60 ng Lef1 MO (K,K'). Co-injection of 0.1 ng Xbra mRNA rescues the downregulation of both Xpo and XmyoD expression by Tcf3 MO (E,E'), but does not rescue their downregulation caused by Tcf1 MO (G,G') or Lef1 MO (L,L'), indicating that while Tcf3 is required for ventrolateral mesoderm development only because it is required for normal mesoderm induction, which is a prerequisite for ventrolateral mesoderm development; Tcf1 and Lef1 are required for ventrolateral mesoderm development independent of any requirement in mesoderm induction. Downregulation of Xpo and XmyoD expression by XlTcf1 MO or XlLef1 MO are both significantly rescued by co-injection of either 0.3 ng XtlTcf1 mRNA (H,H'; M,M') or HA-XlLef1 mRNA (I,I'; N,N'), but cannot be rescued by co-injection of 0.3 ng HA-XlTcf3 mRNA (J,J'; O,O'). (P,P') Numerical summary illustrating penetrance of effects of Tcf/Lef MOs (as labelled) or the co-injection of these MOs with Tcf/Lef mRNAs or Xbra mRNA (as labelled), indicating reduced or absent Xpo expression and XmyoD expression, respectively.