Fig. 3. Fgfr2 and Fgfr3 expression is excluded from the mid/hindbrain junction and repressed by FGF8b. (A,B) Fgfr1 is weakly expressed throughout the embryo at the five-somite stage and E9.5, with the exception of the heart (h in B) at E9.5. (C,D) Fgfr2 is expressed in the brain at E8.5 and E9.5 in the forebrain, rostral midbrain and part of the posterior hindbrain (arrowheads), but excluded from the mid/hindbrain region (asterisks). (E,F) In the brain, Fgfr3 is expressed weakly in the caudal forebrain and part of the posterior hindbrain (arrowheads), but not in the mid/hindbrain region (asterisks) at the five-somite stage and E9.5. Note the strong expression in the extra-embryonic tissues at E8.5. (G,H) Weak and patchy Fgfr1 expression is seen in p1 explants after 48 hours and this expression is not altered by FGF8b-soaked beads. (I) In control p1 explants, strong Fgfr2 expression is limited to the dorsal midline, whereas weak expression is maintained in the rest of the explants. (J) Fgfr2 expression is downregulated by FGF8b-soaked beads. (K) Fgfr3 is maintained in BSA-treated p1 explants, whereas Fgfr3 is repressed by FGF8b-soaked beads (L). Broken lines in B,D,F indicate the tissues used for the explant assays.