Fig. 4. Loss of rostral SHH and FGF8 expression and signaling. (A,B,E,F,K,O) Lateral aspect, (C,D,G,H) ventral aspect and (I,J,M,N) frontal aspect of cephalic region. Wild-type expression of Shh (A,B), Ptch1 (C), Nkx2.1 (D). (E) E8.5 mutant (approx. eight to 10 somites) lacking Shh in RVNM and PrCP (asterisks; n=2). (F) E9.5 (20-25 somites) mutant lacking expression in RVNM (asterisk; n=5). Note loss of Shh expression in first branchial arch (lower asterisk, ba1 in B). (G) Midline mutant lacking rostral Ptch1 expression (asterisk; n=4). (H) Midline mutant lacking rostral Nkx2.1 expression (asterisk; n=2). Wild-type expression of Fgf8 (I,J) and Foxg1 (formerly known as BF-1; K). (M) E8.25 (approx. five somites) mutant with diminished expression of Fgf8 in the ANR which is confined to the midline (asterisk; n=2). (N) E9.5 mutant with diminished Fgf8 expression in the commissural plate and olfactory placodes (asterisk; n=4). (O) Reduced Foxg1 expression (asterisk) in E9.0 (17 somites) mutant. (L,P) Midsagittal sections of E11.5 embryos. (L) In wild type, infundibulum (inf) and Rathke's pouch (rp) interact to form mature pituitary. (P) In midline mutant, infundibulum does not develop (asterisk) and Rathke's pouch is rudimentary. Note cyclopic eye (ey). anr, anterior neural ridge; prcp, prechordal plate; rvnm, rostral ventral neural midline; cp, commissural plate; op, olfactory placodes; fnm, frontonasal mass; md, mandible; ov, optic vesicle. Scale bar: 0.2 mm.

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