Evolution of Gene Regulatory Networks that Control Embryonic Development of the Body Plan

Alteration of the functional organization of the gene regulatory networks (GRNs) that control development of the body plan causes evolutionary change in animal morphology. A major mechanism of evolutionary change in GRN structure is alteration of cis-regulatory modules that determine regulatory gene expression. Both evolutionary conservation and evolutionary innovation must be considered in terms of GRN structure. Here we consider the causes and consequences of GRN evolution, both from an a priori point of view, and in light of extensive recent research on developmental regulatory alterations occurring at different levels of GRN hierarchy. Some GRN subcircuits are of great antiquity while other aspects are highly flexible and thus in any given genome more recent. Both evolutionary conservation and evolutionary innovation occur at the level of whole GRN subcircuits. This mosaic view of the evolution of GRN structure explains major aspects of evolutionary process, such as hierarchical phylogeny and discontinuities of paleontological change and stasis.