Figure 4

Reciprocal induction between Sp8 and Fgf8 in vivo. (a-h) Induction of Sp8 by ectopic expression of Fgf8. Coronal sections of E13.5 forebrains that were electroporated in utero at E11.5 with Fgf8b (a-d) or a control vector (e-h) mixed with EGFP and processed for in situ hybridization using S³⁵ riboprobes for Sp5 (d, h), Sp8 (b, f) and Sp9 (c, g), respectively. Induction of Sp8 was detected in the electroporated domain marked by EGFP (a, e) (arrowheads). Sp5 and Sp9 were not induced by ectopic expression of Fgf8 (c, d). (i-p) Induction of Fgf8 by ectopic expression of Sp8 or the dominant active form of Sp8 (Sp8-VP16). E13.5 brains were electroporated with Sp8 (i, j), Sp9 (k, l), Sp5 (m, n), or Sp8-VP16 (o, p), mixed with EGFP, and processed for in situ hybridization using Fgf8 riboprobes. Fgf8 induction was detected in Sp8 (j) and Sp8-VP16 (p) electroporated brains. Weak induction of Fgf8 was also observed by the electroporation of Sp9 (l), which shares identical btd and Zn-finger domains with Sp8. Fgf8 induction was not detected in brains electroporated with Sp5 (n). Scale bars: 0.5 mm (a-p).