Model for the differential regulation of
odd expression by pair-rule proteins at late phase 2 (
A,
B)
versus mid phase 3 (
C,
D). (
A,
C) Schematic diagrams showing the expression of
odd relative to potential regulators. The horizontal axis represents an idealised portion of the AP axis (~12 nuclei across). The grey vertical lines demarcate a double parasegment repeat (~8 nuclei across). Lighter yellow in (
C) represents fading Hairy expression. (
B,
D) Inferred regulatory interactions. Hammerhead arrows represent repressive interactions. Solid black arrows represent interactions that are currently in operation; dashed grey arrows represent those that are not. At each stage,
odd is expressed only where its current repressors are absent. See
Figure 5 and
Appendix 1—figure 1 for staged relative expression data. Note that the expression patterns of potential regulators diagrammed in this figure represent protein distributions, which often differ slightly from transcript distributions due to time delays inherent in protein synthesis and decay (see
Figure 6).