|
Fig. 5 Correlation between the effect and localization of the clone secreting FGF-8. FGF-8 and β-galactosidase RNA were coinjected at the cleavage stage, and presence of β-galactosidase expression was revealed at early somitogenesis stages, using X-gal staining. The embryos then underwent in situ hybridization using MyoD and AP2 probes. b-galactosidase staining is always seen in the midline of the expanded dorsolateral territory resulting from misexpression of FGF-8 (A-C). When located in the axial midline (D), the FGF-8-secreting clone has no effect on the dorsoventral patterning of the embryo. (E) Dorsal view of an embryo displaying a partial secondary axis phenotype. Optical cross sections through plane S1 (F) or through S2 (G) showing that cells surrounding the FGF-8-secreting clone converge towards this position (arrowhead) instead of converging normally towards the dorsal side of the embryo. (G) The FGF-8 secreting cells are found in both mesoderm and ectoderm. (H,I) Embryo injected with FGF-8 and rhodamine coupled to 2 MDa dextran, visualized in bright field in H at gastrulation. (I) In this embryo, strong fluorescence is seen in the embryonic shield (Sh, delimited by two arrows). (J) In situ hybridization of the same embryo as in H,I using MyoD and AP2 probes at early somitogenesis showing that when located in the axial midline of the embryo at gastrulation, the FGF-8 clone has no effect on the dorsoventral patterning of the embryo. (K,L) When the FGF-8 clone is located opposite to the shield (Sh), the resulting phenotype consists of the formation of a secondary axis (M). (A-E,J,M) Dorsal views; (H,I,K,L) Animal pole views. Ad, Adaxial cells; N, notochord; NC, neural crest.