Fig. 2. fgf8, fgf3 and spry4 are co-expressed during the first 48 hours of embryonic development. (A-H) Blastula and gastrula stages, dorsal towards the right. (A,B) Sphere stage. Expression of fgf8 and spry4 at the dorsal margin. (C,D) Expression of fgf3 and spry4 in the marginal blastoderm of late blastula stage embryos. (E,F) Vegetal pole view of the dorsoventral expression gradient of fgf8 and spry4 at the margin of mid-gastrula stage embryos. (G,H) At late gastrula stages fgf3 and spry4 are co-expressed in the ventral forebrain primordium (arrowhead). (I-N) Segmentation stages. Anterior is upwards in (I,J) and towards the left in (K-N). (I-L) Early segmentation stages. fgf8, fgf3 and spry4 are expressed in the telencephalon (te). (I,J) fgf8 and spry4 display similar expressions in the isthmus, the hindbrain, the somites and the tail bud (tb). (K) fgf3 expression is more restricted in the hindbrain and the tail bud. (M,N) 16-somite stage. Expression of fgf8 and spry4 in the telencephalon, the midbrain-hindbrain boundary (mhb), somites and tail bud. fgf8 but not spry4 is expressed in the anterior unsegmented paraxial mesoderm (upm). spry4 but not fgf8 is expressed in the otic vesicle (ov). (O,P,S,T) 24 hour stage: anterior is towards the left. (O,P) Lateral view. fgf8 and spry4 are expressed in the telencephalon, the epiphysis (ep), the optic stalk (os) and the MHB. (S,T) Dorsal view. Both genes are expressed in the anterior otic vesicle. Posteriorly, fgf8 is detectable in the vesicular epithelium, while spry4 is expressed in adjacent cells outside of the vesicle. (Q,R) 36 hour stage, lateral view, anterior towards the left. fgf3 and spry4 are co-expressed in the branchial arches (ba), the MHB and the otic vesicle. (U-X) 48 hour stage. (U,V) Lateral view, anterior towards the left. fgf8 is expressed in the adenohypophysis, spry4 in the adjacent neurohypophysis. (W,X) Dorsal views of dissected pectoral fins. fgf8 is expressed in the apical ectodermal ridge, spry4 in the underlying mesenchyme.