Partial rescue of the Tbx1 mutant heart phenotype by Fgf8: Genetic evidence of impaired tissue response to Fgf8

► Fgf8 is required in Tbx1-expressing cells for heart development. ► Forced expression of Fgf8 in Tbx1 null embryos failed to rescue the heart phenotype. ► Fgf8, in the presence of low Tbx1 expression partially rescues the heart phenotype. ► Tbx1 null cells are unable to respond to Fgf8 in culture.