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 f
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Abstract 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 wellcharacterized 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.
1 Genomic Information Is Identical in All Cells and Underlies Functional Diversification The genomic sequence encodes the developmental program which determines the progression from fertilized egg to organized body plan. Among individuals within a species, there is little variation of the body plan: the location, form and function of head, thorax, legs, antennae, eyes and so on are all about the same. These individuals share the genetic information required for the development of the body plan. Any changes in the composition of the genetic information leads to I.S. Peter (*) • E.H. Davidson (*) Division of Biology, MC 156-29, California Institute of Technology, Pasadena, CA 91125, USA e-mail: [email protected]; [email protected] V. Capasso et al. (eds.), Pattern Formation in Morphogenesis, Springer Proceedings in Mathematics 15, DOI 10.1007/978-3-642-20164-6_8, # Springer-Verlag Berlin Heidelberg 2013
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fatal errors in the progression of developmental process, as was systematically assessed in sea urchin embryos in the early twentieth century by Theodor Boveri [1, 2]. The same genetic information is present in each cell of an individual, yet these cells will acquire different functions and shapes during development. In development cells function with respect to the organization of the body part to which they contribute, and cellular specialization has to occur in the context of this organization. Functionally, specialization is a stepwise process. Initially, a group of cells is defined whose descendants will form an entire body part. But cells within such “progenitor fields” acquire more and more specialized functions until the entire functional body part is formed, consisting of muscle cells, nerve cells, pigment cells, bone forming cells etc. Where these individual types of cells develop in respect to each other, and in re
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