Boolean Networks in Inference and Dynamic Modeling of Biological Systems at the Molecular and Physiological Level - Biological Networks - page 70

in primordial floral organ cells of wild-type and mutant plants. Furthermore, the
authors also detected the differences in the network architecture of Arabidopsis
thaliana and Petunia hybrids.
In another study the various pathways activated by abscisic acid (ABA) and
leading to stomatal closure were synthesized into an asynchronous Boolean
model (Li et al. 2006). In this model nodes depict a variety of biological
molecules/components such as cytosolic Ca 2+ , ion channels, proteins. The model
identified and verified components leading to ABA hyposensitivity (Gosti et al.
1999; Merlot et al . 2001), insensitivity or impaired closure (Jacob et al. 1999;
Wang et al . 2001; Coursol et al . 2003) as illustrated on Fig. 4.7.
Fig. 4.7. Example output from the asynchronous Boolean model of ABA induced closure. In this
model all nodes are updated in a randomly selected order during each time step. The y axis
represents the percentage of the ON state of the node Closure in a large number of replicate
simulations. Black triangles with dashed lines represent the normal (wild-type) response to ABA
stimulus. Open triangles with dashed lines show that in wild-type, the probability of closure decays
in the absence of ABA. Perturbations in depolarization (open diamonds) or anion efflux at the
plasma membrane (open squares) cause total loss of ABA-induced closure. Figure adapted from
(Li et al . 2006)
Developmental Biology: Drosophila embryonic development (Sanchez et al.
2001; Ghysen et al . 2003; Sanchez et al . 2003) has been studied frequently by
Boolean modeling due to the well established topology of the network and the
classifiable morphological effects of the network perturbations. During the initial
stages of development of the fruit fly Drosophila melanogaster , three families of
genes are successively activated (Sanson 2001): the gap genes, the pair-rule
genes and the segment polarity genes . In two consecutive papers Sanchez and
collaborators studied the gap and pair-rule cross regulatory modules respectively.
The authors implemented multiple levels of activity and multiple thresholds
wherever required. For example, in the case of the pair-rule module, the effect of