Rewiring of an Early Developmental Gene Regulatory Network in Lecithotrophic Sea Urchins
Abstract
The field of evolution and development explores how novelty arises from delicate and highly coordinated developmental processes. As even minor disruptions to development can have catastrophic effects on an organism, studying evolutionary change reveals which developmental processes are most crucially conserved. The sea urchin genus Heliocidaris provides a model in which to explore these questions. The genus contains two closely related species with dramatically different modes of development: the planktotrophic (feeding) species, H. tuberculata, and lecithotrophic (non-feeding) species, H. erythrogramma, diverge only roughly 5 million years, a remarkably short time for such dramatic changes to evolve. H. erythrogramma has an abbreviated larval stage in which major components of the embryo, including a functional gut and structural skeleton are missing. Planktotrophic development, as in H. tuberculata, is characterized by asymmetrical cleavage at the sixteen-cell stage, creating the micromeres which establish the signaling center of the embryo and specify the skeletogenic cell lineage. H. erythrogramma notably does not form micromeres, a major disruption to the understood model of sea urchin development. This document explores how lecithotrophic sea urchin H. erythrogramma establishes the signaling center and the skeletogenic lineage following the loss of the micromeres. In planktotrophic development, micromeres are the first cells to express components of the Wnt signaling pathway, which establishes the anterior-posterior axis of the embryo. Disruptions of wnt signaling in H. erythrogramma indicate that its role in gastrulation and specification of the endoderm are largely conserved across the switch to lecithotrophic development. However, expression patterns of wnt ligands reveal delays in the timing of these signaling events, and rewiring of wnt activity outside of primary axis specification. The micromeres are also the progenitors of the skeletogenic cell lineage. H. erythrogramma skeleton is both delayed and reduced as compared to planktotrophs, indicating disruptions to skeletal development. Using assays and perturbations of components of the skeletal pathway, I have demonstrated that the activation of skeletogenesis has been rewired in H. erythrogramma. However, the downstream pathway appears largely conserved. These results provide groundwork for constructing the developmental gene regulatory network in H. erythrogramma and better understanding how the planktotrophic dGRN evolved.
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Swart, Jane Singleton (2024). Rewiring of an Early Developmental Gene Regulatory Network in Lecithotrophic Sea Urchins. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/31929.
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