Fig. 4. Progressive downregulation of FGF target genes in Fgfr1^f/f;T-Cre mutant embryos after the 6-somite stage. (A-D) Pea3 is normally expressed in control (A) and Fgfr1^f/f;T-Cre (B) embryos at the 5-somite stage, and in 7-somite control embryos (C), but it becomes progressively downregulated in the posterior PSM/tail bud of 7-somite Fgfr1^f/f;T-Cre mutant embryos (D). (E) Real-time PCR for FGF target genes Erm and Pea3 in the posterior tail of Fgfr1^f/f;T-Cre mutant embryos and Fgfr1^f/+;T-Cre control embryos at somite stages 5 (n=1/1), 6 (n=3/5), 7 (n=2/2) and 9 (n=1/1). Both genes become progressively downregulated from somite stages 6 onward. Levels of Erm and Pea3 were normalized to the housekeeping gene Hprt and values are given as the mean change in crossing points (C_T) in Fgfr1^f/f; T-Cre mutant embryos. (F-O) For other target genes (F,G) Erm, (H,I) Gbx2, (J,K) Dusp6, (L,M) Spry2 and (N,O) Sef, the expression in the posterior PSM and the tail bud of E8.75 Fgfr1^f/f;T-Cre mutant embryos is lost, whereas the expression in the anterior PSM and the adjacent structures is normal.