Nodal/Activin Signaling in ES Cell Fate Decisions Figure 7. Oct4 Is a Direct Target of Nodal/Activin Signaling via Graded Phospho-Smad2 Recruitment to the Promoter. UCSC Genome Browser plot of the Oct4 genetic locus showing pSmad2 ChIP-Seq enrichment on the vertical scale in ES cells subjected to Activin (red), DMSO control (blue) and SB (green) treatments with genomic distance in bp on the horizontal scale. Colored bars show ChIP-Seq peak positions and normalized enrichments for each treatment. (B) 503 bp sequence of the Oct4 promoter region marked with asterisk (*) in (A). Sequences in yellow show canonical CAGA SBEs or their inverted sequence TCTG while the strong CAGAC SBE is highlighted in blue. Sequences in red boxes denote where mutations were made in the indicated luciferase constructs. (C) Firefly luciferase assays of the 503 bp sequence cloned into the pGL4.23 reporter construct (pGL4.23 Oct4) or mutated in the strong CAGAC SBE (pGL4.23 m4 Oct4) or mutated in CAGAC and the two flanking CAGA sites (pGL4.23 m345 Oct4). The constructs were transfected into ES cells treated with Activin (dark gray bars), DMSO control (light gray) and SB (white). Discontinuous vertical PLoS Genetics | www.plosgenetics.org 14 June 2011 | Volume 7 | Issue 6 | e1002130