Figure 1.

Segment polarity network and expression pattern of wg and en. (A) The segment polarity gene network model of Ingolia (2004). Ellipses represent mRNAs and rectangles proteins. Lines ending with an arrow and a dot denote activation and repression, respectively. Dashed lines indicate intercellular regulations. The gray line means no direct biological evidence. Nodes are colored into three groups, each of which is represented by one node in (B). (B) The simplified topology of (A). Each node here represents a group of nodes in (A) of the same color. (C) Our model of the segment polarity gene network (see also von Dassow and Odell, 2002). Slp regulates wg positively through the mid gene and its product, which is represented by an arrow from ‘S' to ‘W' in (D). (D) The simplified topology of (C). (E) The initial condition of the patterning function. In three-node networks, ‘S' expresses in the posterior four cells of the parasegment. The pattern is periodic. (F) The final stable pattern. In three-node networks, ‘S' is not fixed to be any specific pattern in the final state. (G) zw3 mutant phenotype. (H) ptc mutant phenotype. Note that (E), (F), (G) and (H) are a simple representation of the actual embryo surface, which is extended in both directions and includes 14 segments.