FGF8 and omphalocele: From these results we conclude that the requirement for Fgf8 expression is in the PSM; the hypothesis that Fgf8 is required in the PSM is further supported by the fact that loss of Fgf17 in TCre;Fgf8f/Δ mutants promoted omphalocele (Fig. 2G), and Fgf17 is expressed in the PSM but not the somites (Fig. 1).