Fig. 3. Fgf3 and Fgf8 regulate telencephalic gene expression. Dorsal (A-D,M-P) or lateral (E-L,Q-T) views with anterior to the left. (A-D) emx1 expression at the anterior margin of the forebrain primordium at tailbud stage. (A) emx1 transcripts are detected in the presumptive anterior forebrain in control embryos but are reduced in embryos injected with Fgf8mo (B), and are undetectable in embryos injected with either Fgf3mo (C), or Fgf8mo and Fgf3mo (D). (E-H) emx1 expression at 24 hpf. (E) emxl expression is limited to the pallial telencephalon in control embryos. Arrow indicates expression boundary. emx1 transcripts are detected in both pallial and subpallial (arrow in F) telencephalon in embryos injected with Fgf8mo (F), Fgf3mo (G), or Fgf8mo and Fgf3mo (H). (I-L) tbr1 (red) and dlx2 (blue) expression at 24 hpf. (I) A control embryo: dlx2 transcripts are found in the ventral thalamus and subpallial telencephalon, and extend into the posterior region of the pallial telencephalon. tbr1 transcripts occupy the pallial telencephalon. (J) tbr1 expression extends into the anterior subpallial telencephalon, partially overlapping dlx2 expression, in embryos injected with Fgf8mo (compare arrows in I and J). tbr1 and dlx2 expression is reduced following injection with either Fgf3mo (K), or Fgf8mo and Fgf3mo (L). (M-P) Telencephalic eom expression at 24 hpf. (M) eom transcripts are detected in the telencephalon in control embryos. eom transcripts in the telencephalon are reduced or undetectable in embryos injected with Fgf8mo (N), Fgf3mo (O), or Fgf8mo and Fgf3mo (P). (Q-T) 28 hpf embryos, bisected along the AP axis, and mounted to show the internal brain surface following detection of fgf3 (blue) and dlx2 (red) transcripts. (Q) Control embryos express dlx2 in the telencephalon and ventral thalamus, and fgf3 in hypothalamus (and isthmus). (R) fgf3 transcripts (arrow) are upregulated in the telencephalon in the absence of Fgf8. Loss of Fgf3 (S), or both Fgf3 and Fgf8 (T), results in the absence of dlx2 expression. d, diencephalon; tel, telencephalon.

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