Fig. 7. Fgf15 and Fgf receptor expression in the diencephalon and midbrain of wild-type (A,B,D,F,H,J,L,N) and Shh (C,E,G,I,K,M,O) mutant embryos. (A) Fgf15 and Shh expression. (B-G) Fgf15, (H-K) Fgfr2 and (L-O) Fgfr3 expression. (A) At the 12-somite stage, Fgf15 (purple) was strongly expressed in the ventral regions of the diencephalon (white arrow), dorsal to the Shh expression domain (white arrowhead, brown). Black arrows indicate the ventral Shh expression domain in the midbrain. (B) A lateral view reveals the extent of ventral expression of Fgf15 in the brain. Note that Fgf15 expression was undetectable in dorsal regions of the diencephalon and midbrain at this stage. (D,F), Fgf15 shows a ventral to dorsal expansion from the 12- to 16-somite stage in diencephalic and midbrain primordia of wild-type embryos. (C,E,G), Shh mutants showed no expression of Fgf15 in the caudal diencephalon and anterior midbrain at all stages examined, whereas expression at the midbrain/hindbrain isthmus (arrow) remains in Shh mutants. Expression of Fgfr2 in the diencephalon and anterior midbrain in wild type (H,J) extends ventrally in Shh mutants (I,K). Downregulation in the expression of Fgfr3 (compare L,N with M,O) correlates with the growth defect in these regions of Shh mutants. Arrowhead indicates the diencephalon-midbrain boundary. Scale bars: 100 µm.

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