Fig. 3. The R-module and intron have different temporal expression profiles and are both influenced by autoregulation by Nodal signaling. (A) Kinetics of luciferase expression levels driven by the R-module EpGluc, intron EpGluc and control EpGluc constructs. (B) Comparison at the hatched blastula stage of the transcriptional activities of R-module, intron, R-module Smad(-) (i.e. lacking the binding sites for Smads) and intron Smad(-) in normal sea urchin embryos and embryos injected with the Nodal morpholino or treated with the Alk4/5/7 inhibitor SB431542. The data are presented as the ratio of luciferase expression between EpGluc and the wild-type module.