Fig. 1.

The blimp1 and wnt8 subcircuit of the gene regulatory network for endomesoderm specification in Strongylocentrotus purpuratus (Smith et al., 2007). (A) Diagrammatic illustration of the dynamic torus pattern of gene expression, as exemplified by wnt8 and blimp1. (B) GRN subcircuit. Regulatory relationships are shown between blimp1, β-catenin/Tcf, GSK-3, and wnt8; nb-Tcf, complex of nuclear β-catenin and Tcf transcription factor. The lines leading from nb-Tcf bifurcate into an arrow and a repression bar, indicating that in the absence of nuclearized β-catenin the Groucho/Tcf complex acts as a dominant repressor at both the wnt8 and blimp1 loci. Positive inputs from both Blimp1 and nb-Tcf thus control wnt8 transcription (Minokawa et al., 2005). The three predicted inputs into the blimp1 cis-regulatory module(s) are indicated: a permissive input from nb-Tcf; activation by Otx; and autorepression.