Fig. 4. Regulation of the chick Cer left-side enhancer by Shh, FGF and Nodal signaling pathways. (A-F) Analysis of Cer-EGFP expression in the left-side mesoderm (LSM) of embryos electroporated at HH4-5 and fixed at HH8-9. (G,H) Analysis of Cer-EGFP expression in the anterior mesendoderm (AM) of embryos electroporated at HH3 and fixed at HH6. (A-D) Chick embryos were electroporated with Cer0.4-EGFP and grafted with beads (arrowheads) soaked in Shh protein (A), the FgfR1 inhibitor SU5402 (B), phosphate-buffered saline (PBS, control; C) or Nodal protein (D). EGFP expression was ectopically induced on the right side by Shh, SU5402 and Nodal (arrows). (E-H) Effect of the Nodal antagonist Xenopus CerS (XCerS) on chick Cer (cCer) left-side enhancer activity. Chick embryos were electroporated either with pCAGGS-RFP and PCR5-EGFP (control; E,G) or with these plus pCAGGS-XCerS (F,H). XCerS repressed the transcription of PCR5-EGFP in the LSM (E,F), whereas it had no effect on AM expression (G,H). AM, anterior mesendoderm; LSM, left-side mesoderm; XCerS, Xenopus CerS.