Fig. 3. Wild-type expression of Chrd, Nog and Bmps. (A-H) Frontal aspect of headfold stage (E7.75) embryos. Bracketed area represents approximate extent of Gsc expression, a prechordal plate (PrCP) marker. (A) Chrd is not expressed in the rostral-most PrCP (asterisk). (B) Shh and (C) Foxa2 are expressed in all midline mesendoderm, including rostral PrCP (double arrows). (D) Gsc is expressed throughout the PrCP. (E) Nog is not expressed in the rostral PrCP (asterisk), but is expressed in the ANR (arrows). (F-H) BMPs antagonized by CHRD and NOG are expressed in surface ectoderm (se), rostral paraxial mesoderm (arrowheads), node (n) and midline mesendoderm (mse). Bmp7 is not expressed in the rostral PrCP (H, asterisk). (I-K) Lateral aspect of bisected three-somite stage embryos. Neither Chrd (I) nor Nog (J) is detected in rostral PrCP at this stage by in situ hybridization, although Shh (K) is present (arrows). Chrd (L) and Nog (M) are both expressed throughout the rostral axial mesendoderm by the five-somite stage (arrows) and in head mesenchyme (arrowheads). Scale bar: 0.2 mm. (N) RT-PCR analysis of Chrd and Nog expression. Chrd and Nog are detected in the midline and trunk after 30 cycles of PCR (lanes 1,3). Nog is evident in the ANR (lane 4) after 30 cycles, and Chrd after additional amplification.