Fig. 6. Inhibition of retinoid signaling alters expression of regulatory genes in the forebrain and FNP as shown by in situ hybridization on parasagittal sections 72 hours after bead implantation at stage 10. (A) FGF8 is normally expressed in the rostral neural tube, including the optic recess (o) and isthmus (i). (E) In antagonist-treated embryos, FGF8 expression is lost in the rostral neural tube, although low levels can be detected in the truncated diencephalon (d). (B) Normal BF1 expression marks most of the telencephalon (t) and hypothalamus (ht). (F) In antagonist-treated embryos, expression of BF1 is not detected in the remnant of the forebrain except some expression remains in the malformed hypothalamus. (C) SHH is normally expressed in ventral neural tissues, including the hypothalamus and basal telencephalon. (G) In antagonist-treated embryos, SHH expression is lost in the diencephalic remnant. (D) Normal PAX6 expression marks dorsal forebrain structures up to the midbrain (m) and the eye (not shown). (H) In antagonist-treated embryos, PAX6 expression is expanded into the remaining diencephalon (d) and can also be detected in the eye (e) and hypothalamic remnant. (I) Normally, OTX2 is broadly expressed in the forebrain and midbrain. (M) In antagonist-treated embryos, OTX2 expression is maintained in these domains. The expression of PAX6 and OTX2 serves as an important control, demonstrating that loss of expression is due to RAR/RXR antagonist-induced misregulation of target genes, rather than a general inability of remaining tissues to synthesize mRNA transcripts. (J) Normally, NKX2.1 marks most of the hypothalamus and basal telencephalon. (N) In antagonist-treated embryos, residual NKX2.1 expression remains in the hypothalamic remnant. (K) Normally, NKX6.1 marks the basal plate. (O) In antagonist-treated embryos, NKX6.1 expression persists in the basal plate of the midbrain but not in the residual forebrain. (L) Normally, DLX2 expression marks part of the hypothalamus, all of the basal telencephalon, and mandibular arch (ma) neural crest. (P) In antagonist-treated embryos, DLX2 expression persists in the hypothalamic remnant and in the mandibular arch. Scale bars: 100 µm.