Gene regulatory network evolution and the origin of biological novelties

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DESCRIPTION (provided by applicant): Cells acquire their unique fates by the differential pathways of combinatorial gene activity during the developmental period. Gene regulatory networks (GRN) controlling the specification of endomesodermal cell fates have been constructed in a handful of model systems, include sea urchins, vertebrates, and nematodes. Endomesodermal precursors that give rise to endodermal (gut derivatives) and mesodermal (muscle, blood, coelom, kidney and skeletal elements) cell types become distinct from ectodermal precursors (that give rise to epidermis and nervous system) by differential gene expression. Separate endodermal and mesodermal fates are then specified subsequently from endomesodermal precursors. Understanding the relationship between intracellular factors and extracellular signals, and reconstructing gene regulatory networks between different animal species can provide key insights in how and when the molecular and morphological characters of each organism are built. A prime example is the original evolutionary appearance of the mesodermal germ layer in animal evolution. Cnidarians (anemones, corals, and "jellyfish") are an animal group whose adults possess derivatives of only two germ layers, ectoderm and a bifunctional (having both absorptive and contractile functions) gastodermal (gut) layer. Cnidarians are the closest living relatives of other bilaterally symmetrical animals that possess all three germ layers, and compelling molecular, genomic, developmental, and evolutionary evidence exists to demonstrate that the cnidarian gastrodermis is the evolutionary precursor of both endodermal and mesodermal germ layers in all other triploblastic bilaterian animals. Thus, unraveling this cnidarian "endomesodermal" gene regulatory network, will provide necessary insight into how GRN sub circuits have been adopted, rewired or co-opted in various metazoan in order to give rise to novel, modified or specialized endomesodermal features. This grant will functionally reconstruct the gene regulatory network underlying endomesoderm formation in the cnidarian sea anemone Nematostella vectensis, (whose genome has been sequenced by the J.G.I (Dept. Energy), using, QPCR, whole genome microarrays, functional techniques such as pharmaceutical drug treatments, synthetic mRNA misexpression, translation and splice blocking morpholino approaches and cis-regulatory analysis. In addition, we will implement all the obtained data into an already existing gene expression database in order to share our findings with the scientific community. The generation of high quality molecular data from a phylogentically pivotal species for the first time will help explain the differences seen in genes and their regulatory interactions previously identified in bilaterian model systems by polarizing the direction of evolutionary change. PUBLIC HEALTH RELEVANCE: Project Narrative Individual cells in developing animal embryos learn their ultimate fate by the sequential differential activation of specific genes contained in each cell's genome. We have learned a great deal about how these genes functionally regulate each other in complex gene regulatory networks (GRN) in a handful of model species. This grant uses a powerful new model system to functionally understand how endodermal (gut) and mesodermal (e.g. muscle, blood, bone, kidney) arose from a common endomesodermal precursor. These novel data will provide insight into the significance of variations in the GRNs in different systems and suggest specific gene interactions involved in abnormalities in endomesodermal development.