Fig. 6

Fig. 6 syu;cyc double mutants lack all floor plate structures in the trunk and primary motor neurons are strongly reduced. Dorsal (A, C, E, G), and lateral views (B, D, F, H; anterior is left) of wild-type (A, B), cyc^tf219 (C, D), syu^tbx392 (E, F), and syu;cyc double-mutant (G, H) embryos stained with probes specific for fkd4 (A, C, E, G) and an antibody against Islet1 (B, D, F, H) in the pharyngula period. In cyc embryos fkd4-expressing LFP cells are formed (C), whereas in syu embryos MFP cells are present and LFP are not formed (E). In syu;cyc double mutants fkd4-expressing cells in the ventral neural tube can be detected, indicating the complete absence of floor plate structures in these double mutants (G). However, fkd4 expression in the hypochord underneath the notochord and in the hindgut remains unchanged (data not shown). Primary motor neurons stained with an antibody against Islet1 are present in cyc and syu single mutants (arrowhead in D, F), but strongly reduced in syu;cyc double mutant embryos (arrowhead in H), indicating that shh together with a signal(s) from the MFP induces primary motor neurons. The few remaining motor neurons might be induced by ehh expression in the notochord.