A Discrete Model of Drosophila Eggshell Patterning Reveals Cell-Autonomous and Juxtacrine Effects
Figure 2
Phenomenological model: rules and result.
(A) Regulatory graph: the model links three distinct follicle cell fates, Operculum, Floor and Roof, to a combination of input components EGF, BMP, anterior, and Roof_adj. Oval nodes are Boolean (0 or 1) and the rectangular node (EGF) is associated to a multi-valued variable, which here takes values between 0 and 2 (absent, intermediate and high level). EGF directly influences the position of the three domains on the dorsal-ventral axis. BMP establishes the anterior border of the roof, while anterior defines the anterior competence region. Roof_adj is an input variable accounting for the differentiated state of neighboring cells. Green and red edges denote positive and negative effects, respectively. The edge in purple denotes a dual effect, i.e. activating or repressing, depending on the level of its source. (B) Logical functions driving the dynamics of the model: Each rule specifies under which conditions the variable evolves to value 1 (otherwise, the variable tends to 0). The condition of the presence of EGF is simply denoted as “EGF”, and “EGF:1” or “EGF:2” whenever distinction between levels is required. Logical connectors are: & for a conjunction (and), | for a disjunction (or) and ! for a negation (not). (C) Epithelial model: left, patterns for the inputs EGF (yellow), BMP (purple) and anterior (pink) as used during the simulation. Right, final cell fates are shown in green (operculum), blue (floor) and red (roof).