Nodal/Activin Signaling in ES Cell Fate Decisions Figure 1. Pitx2, Lefty2, and Smad7 Are Transcriptional Targets of Graded Nodal/Activin Signaling. Real-time PCR quantification of changes in mRNA levels for (A) Pitx2, (B) Lefty2 and (C) Smad7 in mouse ES cells during a 0 to 24 hours time course under graded Nodal/Activin signaling conditions. High signaling was induced by direct treatment with 25 ng/ml Activin (red), low signaling with 10 uM of SB431542 inhibitor (green) and a control treatment with 1/5000 dilution of DMSO carrier (blue) was carried out following pretreatment of all cells for 6 hours in chemically defined KSR media with 10 mM SB (26 to 0 hours). b-actin was used as a housekeeping control and error bars show s.e.m for n = 3 replicates. doi:10.1371/journal.pgen.1002130.g001 PLoS Genetics | www.plosgenetics.org 4 June 2011 | Volume 7 | Issue 6 | e1002130