FGF4 regulates blood and muscle specification in Xenopus laevis

Background information: FGF signaling is known to be required for many aspects of mesoderm formation and patterning during Xenopus development and has been implicated in regulating genes required for the specification of both blood and skeletal muscle lineages. Results: In this study, we specifically knock-down the expression of FGF4 (eFGF) using antisense morpholino (AMO) mediated inhibition and demonstrate that FGF4 acts in the dorsal marginal zone to restrict blood development and promote the development of skeletal muscle. In addition, we use a drug inhibitor of FGF signaling and an inducible form of FGFR1 to identify a period of competence during late blastula and gastrula stages when FGF signaling acts to regulate blood versus muscle specification. Notably we find that it is the dorsal activity of FGF that is required to restrict the expression of SCL to the ventral blood island. Conclusions: Our data indicate that FGF4 is a key organizer derived signal involved in the process of dorsoventral patterning of the mesoderm.