Fig. 2. SRF inhibits Activin/Nodal signaling. (A) Wild-type XSRF inhibited the induction of mesendoderm markers by Activin or Xnr1 in animal caps. Embryos were injected at the four-cell stage in the animal pole region with wt XSRF mRNA (2 ng) with or without Xnr1 mRNA (50 pg), and then the animal caps isolated at stage 8.5 were cultured in the presence of Activin protein (10 ng/ml, for animal caps without Xnr1 injection) until stage 10.25 and then subjected to RTPCR analysis. ODC, ornithine decarboxylase as a loading control; -RT, a control of RT-PCR on stage 10.25 whole embryo in the absence of reverse transcriptase; Uninjected, uninjected control. (B) HepG2 and (C) Mv1Lu cells were transiently transfected with a control vector or SRF along with ARE-Luc and FAST-1. Cells were harvested 36 hours after transfection for luciferase assays. ß-Galactosidase activities were used to normalize for transfection efficiency. All luciferase asssays were performed in triplicate.