Fev directly regulates ERK signaling. (A) erk2 mRNA can partially rescue the expression of runx1, cmyb, and rag1 in the AGM and thymus of fev morphants. The AGM region and thymus are indicated by arrows in black and red, respectively. Anterior to the left. (B) qPCR analysis of runx1 expression in control embryos, fev morphants, and rescued embryos by overexpression of erk2 mRNA (mean ± SD, n = 3, *P < .05). (C) Western-blot analysis of Runx1 expression in fev morphants and rescued embryos. (D) The Fev core binding motif and the erk2 promoter. a, The conserved core binding site of Fev. b, The schematic structure of the erk2 promoter. CF/CR are control forward and reverse primers, which are used to amplify the erk2 promoter region without the conserved Fev binding site. erk2-1F/1R represent primers used to amplify the promoter region with the conserved Fev binding site. erk2p means the erk2 promoter construct with the wild-type Fev binding site; erk2p^∆ means the erk2 promoter construct with mutated Fev binding site. (E) ChIP assay showed that Fev directly binds to the erk2 promoter region. (F) Reporter assay with the promoter constructs of erk2, which contain the conserved or mutated ETS binding sites, cotransfected with pCDNA3.1(+)-fev plasmid.