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Fig. 5 Expression of fgf8 and the Fgf-target gene spry4, during early eye development. At the 5-somite stage, fgf8 and spry4 are co-expressed in the telencephalon dorsal to the diencephalic evagination zone of the optic vesicles (A-D) in wild-type embryos. spry4 expression extends from the telencephalon into the diencephalon, including the proximal future nasal part of the evaginating optic vesicle (arrowheads in D) and is found in the nasal placode precursor cells (npp) (D), surrounding the telencephalon at this stage. (E,F) In ace, telencephalic and diencephalic spry4 expression is reduced (arrowheads in F), but expression in the nasal placode precursor cells is unaffected. Orientation of dorsal views (A,C,E,) indicated in A; orientation of transverse sections at a intermediate anterior-posterior level of the optic vesicle (B,D,F) indicated in B. A, anterior; P, posterior; Pr, proximal; Di, distal; D, dorsal; V, ventral; tel, telencephalon; ov, optic vesicle; npp, nasal placode precursors. Broken lines represent outlines of the optic vesicle (A,C,E,) and neural tube (B,D,F).