Expression of Fgf4 during early development of the chick embryo.

Fibroblast growth factor 4 (Fgf4) has been implicated as a regulator of mesoderm formation, posteriorisation, neural induction and neural patterning. Much of the evidence for this derives from studies in which exogenous FGF4 is applied to avian embryos. We have therefore examined expression of endogenous Fgf4 mRNA in the developing chick embryo at stages when these processes are occurring. Expression was detected in the primitive streak from the onset of gastrulation. Notably, transient expression of transcripts was found in head process cells at the onset of neural plate formation and regionalisation. Later, mRNA was detected in the presumptive posterior hindbrain and within the ventral midbrain. Fgf4 mRNA was also found in paraxial mesoderm underlying the posterior hindbrain, somites, branchial arches, limb buds and the tail bud.