Figure 3.

The gene regulatory network (GRN) model of the animal ectoderm up to mesenchyme blastula stage. This GRN model includes features relevant to the step-wise establishment of regulatory states. The circuitry shows direct and indirect Nodal signaling effects involved in ectodermal gene expression, and the double negative gate logic mediated by ets4 and sip1 clearance, which provides both spatial and temporal restriction of oral ectodermal and stomodeal gene expression. The targets of these double negative gates include gsc, foxg and bra.