HLH-1 and the C. elegans body wall muscle transcriptional differentiation network

摘要

To understand the structure and function of gene regulatory networks, it is important to first catalogue the components. Measurable constituents of networks include cis-regulatory elements, identified by their conservation and ability to drive expression; transcription factor binding motifs, identified by protein binding; transcription factors, identified by their necessity in network function; and target genes, identified by their conditional expression. The heart of a regulatory network is the transcription factor, which is dedicated to its role in the network. Transcription factors must be activated and regulate downstream targets in a discrete and reproducible fashion. Any deviation in network function may result in the collapse of the network and death of the animal. Thus, a network must be robust enough to function under a variety of biological conditions. However, network redundancies are inefficient in terms of fitness and lost during the course of evolution. The network structure and function reflects these evolutionary realities: strong sequence conservation of cis-regulatory elements coupled with widespread stochastic transcription factor binding, and ancient transcription factor conservation coupled with overlapping activation of targets. The evolution of functional transcription factor networks therefore must be a balance between conservation and flexibility.