Pattern Formation in Sea Urchin Endomesoderm as Instructed by Gene Regulatory Network Topologies

Animals consist of body parts which are spatially discrete functional units. The spatial separation of these body parts and the diversification of their function and structure are developmentally controlled by gene regulatory networks. The transcription factors and signaling molecules which participate in the spatial organization of a developing organism are components of these networks. The causal linkages in the network consist of the regulatory interactions of each factor with its target genes. Interactions among different regulatory genes are responsible for forming specific spatial patterns of gene expression. The architecture of these regulatory interactions and how they instruct the formation of specific spatial domains is directly determined by the genomic sequence. In the sea urchin embryo, many such spatial domains are established early in development. A well-characterized gene regulatory network underlies the specification of endodermal and mesodermal regulatory domains in this embryo. We review multiple examples which reveal the causal logic underlying genomic control strategies for pattern formation during sea urchin embryogenesis