Gene regulatory network circuits in context. (A) Double negative gate, used for sea urchin embryonic skeleton specification [31]. Skel: in skeletogenic precursors. Non-Skel: in rest of embryo. Horizontal lines with bent arrows: genes. Arrows: positive regulation. Bar-end lines: negative regulation. Grayed out: inactive/non-expressed. (B) Eric Davidson, 2010, in Berlin. (C) Core regulatory network for hematopoietic stem and progenitor cells [60], with inputs to genes transduced via discrete cis-regulatory elements (rectangles). Note dense positive cross-regulation. (D) Feed-forward circuit, example from pro-T cell lineage commitment [68]. (E) Mutual repression-based bistable circuit, GATA1 vs. PU.1 [69].