The segment polarity network is a robust developmental module

Abstract

All insects possess homologous segments, but segment specification differs radically among insect orders. In Drosophila, maternal morphogens control the patterned activation of gap genes, which encode transcriptional regulators that shape the patterned expression of pair-rule genes. This patterning cascade takes place before cellularization. Pair-rule gene products subsequently 'imprint' segment polarity genes with reiterated patterns, thus defining the primordial segments. This mechanism must be greatly modified in insect groups in which many segments emerge only after cellularization. In beetles and parasitic wasps, for instance, pair-rule homologues are expressed in patterns consistent with roles during segmentation, but these patterns emerge within cellular fields. In contrast, although in locusts pair-rule homologues may not control segmentation, some segment polarity genes and their interactions are conserved. Perhaps segmentation is modular, with each module autonomously expressing a characteristic intrinsic behaviour in response to transient stimuli. If so, evolution could rearrange inputs to modules without changing their intrinsic behaviours. Here we suggest, using computer simulations, that the Drosophila segment polarity genes constitute such a module, and that this module is resistant to variations in the kinetic constants that govern its behaviour.

Gene duplications, robustness and evolutionary innovations

“…Other examples come from regulatory gene networks, such as the molecular network specifying fruit fly segments. Such networks may tolerate much quantitative variation in interactions among network genes [2][3][4][5] . Examples at the highest level of organization include macroscopic traits.…”

Diverse metabolic model parameters generate similar methionine cycle dynamics

“…A series of recent modeling studies have made major strides towards identifying topological features of bionetworks that give rise to emergent properties such as the ability to sense and respond to environmental signals, maintain metabolic homeostasis, and form complex developmental patterns, all in a manner that is robust to environmental and genetic noise (Barkai and Leibler, 1997;Bhartiya et al, 2006;Brandman et al, 2005;Kollmann et al, 2005;Meir et al, 2002;Stelling et al, 2002;von Dassow et al, 2000;Wagner, 2005). A complement to understanding the topological features of bionetworks that lead to their qualitative properties is finding the precise parameter values which lead to specific quantitative phenotypes.…”

Microfluidics-based systems biology

“…Hunchback expression variability increased most significantly during a temperature reversal between 65 min and 100 min, indicating that this development period is the most critical for compensatory mechanism activity. Mathematically, von Dassow et al 28 demonstrated that the Drosophila segment polarity network is robust due to the intra-and inter-cellular topology of the system. To this end, an entire Drosophila protein-protein interaction map has been developed.…”