Chapter 5 - Gene Regulatory Networks: The Roots of Causality and Diversity in Animal Evolution

Abstract

This chapter focuses on the evolutionary implications of the structure and function of gene regulatory networks. Changes in given functional linkages of gene regulatory networks occur at the DNA level by alteration of the cis-regulatory sequence defining transcription factor target sites. Differentiation genes are uniquely positioned in the regulatory network structure, residing at the periphery of the network. Unlike all genes that constitute the internal structure of the network, their products do not have the function of controlling other genes. The constraints on evolutionary change in differentiation gene battery function are directly subject to selection, since they produce in detail most of the phenotypic functionalities with which the animal confronts its environment. The body plan is encoded in the internal regions of the gene regulatory network, which during development determine the progression of spatial regulatory states, not the business of differentiation gene batteries. Many of the gross regional effects of hox gene gain or loss of function mutations on morphology that have been logged over the last several decades are reminiscent of evolutionary diversification.